Encyclopedia Of Animal Science - S ppt

Salmon Barbara Grisdale-Helland AKVAFORSK, Sunndalsøra, Norway Stale J Helland ˚ Aquaculture Protein Centre CoE, Sunndalsøra, Norway Kari Kolstad ˚ AKVAFORSK, As, Norway INTRODUCTION The production of farmed salmon for food started in the 1960s, aided by experience from the production of young salmon and trout for release in rivers Since that time, selective breeding programs and improved feeds and management have contributed to the tremendous growth in the salmon industry During the period 1985 2001, the world production of farmed Atlantic salmon (Salmo salar) increased from 38,797 T to 1,025,287 T In 2001, Norway and Chile produced 43% and 25% of the Atlantic salmon, respectively Atlantic salmon are grown in fresh water to a size of about 70 g and are then transferred to cages in the sea where, during the next 12 months, they grow to a market size of to kg The main ingredients in salmon feed are fish meal and fish oil, although the use of alternative sources of protein and fat is increasing The optimal dietary protein level for salmon is higher than for terrestrial species because fish use a higher proportion of the protein for energy Despite this, the proportion of consumed protein retained in the edible portion of salmon is about 30%, two times higher than for chickens and pigs PRODUCTION The Salmonidae family includes the genera Salmo, Oncorhynchus, and Salvelinus, comprising the salmon, trout, and char Atlantic salmon have been held in culture for release in rivers since the 1800s, and in a farming situation for food production since the 1960s Atlantic salmon make up the greatest part of the world production of the various salmon species, 1,025,287 T in 2001.[1] Four countries Norway, Chile, the United Kingdom, and Canada produce almost 90% (Fig 1), the rest being produced by eight other countries Of the Pacific salmon species, the production of coho salmon (Oncorhynchus Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019790 Copyright D 2005 by Marcel Dekker, Inc All rights reserved kisutch) (151,386 T in 2001) is greatest, 90% of it being produced by Chile (Fig 2).[1] The production of Atlantic salmon has increased as a result of greater numbers of fish being farmed using continuously improved genetic material, nutrition, and management The cost of production per kg round weight (not including slaughter and packaging costs) in 1997 was US $2.495 in Norway and US $1.986 in Chile, the main differences being smolt costs and undefined miscellaneous costs.[2] Feed (including pigments, vitamins, medication, and feed transport) accounted for 51% of the production costs in Norway and 61% in Chile.[2] In 2001 in Norway, 306,328 kg salmon were produced in the sea-phase per man-year, a 58% increase from 1997.[3] LIFE CYCLE Most salmon are anadromous In the wild, spawning, fertilization and hatching of roe, and an initial growth period occur in rivers This is followed by migration to sea and the main growth period, and later, as mature fish, migration back up the river to reproduce This cycle is duplicated in culture conditions Mature Atlantic salmon are stripped for roe (eggs) and milt (secretion containing the sperm), these are mixed to allow fertilization, and then the eggs are hatched, all in fresh water The alevin (young fish) lives off its yolk sac until it has developed enough to be able to consume exogenous feed Growth continues in freshwater tanks until the fish has undergone a physiological transformation, smoltification, allowing it to survive the hyperosmotic conditions of salt water With artificial light regimes and good husbandry, the smoltification process may be started early so that smolt are produced during the first autumn, although usually this process occurs later and the fish are not transferred to sea cages until the second spring Atlantic salmon grow to a market size of to kg during a period of about 12 months in the sea Fish chosen for 777 778 Salmon Fig World production of Atlantic salmon, in thousands of tons (round weight) (From Ref 1.) (View this art in color at www.dekker.com.) broodstock are moved back to fresh or brackish water a few months before spawning NUTRITION AND FEEDING During the period 1994 1998, the feed efficiency ratio for Norwegian Atlantic salmon production was approximately 0.83 kg gain per kg dry feed.[4] The amounts of raw materials used for salmon feed production in Norway in 1999 and 2000 indicate that the average feed was made up of 40% fish meal and fish silage, 7% corn and wheat gluten, 6% various soybean products, 28% fish oil and 3% soybean oil, 12% wheat flour, and 4% vitamins, minerals, and pigment.[4] The optimal dietary protein level for salmon is higher than for terrestrial species because fish use a higher proportion of the protein for energy Despite this, the proportion of consumed protein retained in the Fig World production of coho salmon, in thousands of tons (round weight) (From Ref 1.) (View this art in color at www.dekker.com.) Salmon edible portion of salmon is about 30%, two times higher than for chickens and pigs.[5] The fat level in diets for Atlantic salmon fed in sea cages has been increased from an initial level of under 10% to a current level of up to 40%, due to developments in extrusion and vacuum coating of fat Salmon not have a requirement for carbohydrates, but sources such as wheat and corn are added to the formulation to aid in binding of the feed and expansion during extrusion Salmon poorly digest high levels of dietary starch The increase in efficiency of production of salmon has been aided by the development of computerized feeding methods and equipment Systems are available that register the amount of feed refusal and thereby the feeding activity of the fish in the cage and subsequently, increase or decrease the ration size and/or frequency of feeding In grow-out farms, photoperiod manipulation with underwater lights is used to delay or prevent maturation before harvest, thereby reducing or avoiding the reduction in growth and flesh quality often accompanying reproductive development.[6] QUALITY The main factors describing the quality of farmed salmon are color, flavor, fat content and distribution, texture, and appearance These may be influenced by species and strain of fish, age and weight, feed composition, ration level, and genetic selection Preference differences between markets and by the processing industry for certain characteristics influence the type of fish that are produced The intake of fish (and n-3 polyunsaturated fatty acids) is generally associated with a lower risk of coronary artery disease in humans, although the exact reason for this connection has not been defined.[7] Because of limited supplies of fish meal and fish oil, the use of other protein and lipid sources for fish feed, from plants for example, is expanding The fatty acid composition of fish flesh is highly influenced by the dietary fatty acid content, though, and diets containing plant oils with higher levels of n-6 fatty acids and lower levels of n-3 fatty acids result in a reduction in the flesh n-3/n-6 fatty acid ratio A subsequent period of feeding a diet containing only fish oil, however, may partly or completely reverse the changes in the levels of the various fatty acids caused by plant oils.[8] 779 the first breeding program for Atlantic salmon was established For the first two generations of selection, the breeding goal was growth rate With an increase in growth of 14% in each generation of selection,[10] after seven generations of selection, the time needed to reach slaughter weight is now halved The fresh water period has decreased from 16 to eight months, while the growout period in sea has decreased from 24 to 12 months This has resulted in a considerable reduction in production costs, mainly through improved feed efficiency Domestication is also an important consequence of selective breeding by selecting the highest performing individuals in each generation under famed conditions The breeding goal is now more complex in accordance with environmental challenges and demands in the market Characteristics such as age at sexual maturation, meat quality (fat percentage and distribution and flesh color), and disease resistance are important parts of the breeding goal The breeding program has, from the start, been based on family selection, utilizing family information to select breeding candidates This selection method has proven to be the most efficient in Atlantic salmon.[11] It is expected that knowledge from extensive research in the area of molecular genetics can be applied in future breeding programs.[12] Molecular information connected to important traits may be utilized to increase genetic progress Further, the use of microsatellite DNA profiling for family identification may be possible in the future, which represents a major advance in selective breeding of aquatic species, allowing different family groups to be kept in a common tank from fertilization onward CONCLUSION It is expected that the production of farmed salmon will continue to grow, despite small economic margins, as new markets are established and further improvements in production efficiency are made An increase in the use of more readily available plant protein and fat sources and appropriate management techniques will help maintain sustainable production of this healthy, high-quality food ACKNOWLEDGMENT Arne Kittelsen is gratefully acknowledged for help and discussions during the preparation of this manuscript BREEDING AND GENETICS ARTICLES OF FURTHER INTEREST In Norway, extensive breeding experiments with Atlantic salmon and rainbow trout were started in 1971.[9] In 1975, Aquaculture: Production, Processing, Marketing, p 48 Aquatic Animals: Fishes Major, p 52 780 Aquatic Animals: Fishes Minor, p 55 Contributions to Society: Conversion of Feed to Food, p 245 REFERENCES FAO Aquaculture Production: Quantitites 1950 2001; FAO Yearbook, Fishery Statistics, Aquaculture Production 2001; Food and Agriculture Organisation, 2001; Vol 92/2 http://www.fao.org/fi/statist/fisoft/fishplus.asp (accessed April 2003) Bjørndal, T.; Aarland, K Salmon aquaculture in Chile Aquacult Econ Manage 1999, 3, 238 253 Norwegian Directorate of Fisheries Lønnsomhetsundersø kelse for matfiskproduksjon laks og ørret 1konomiske Analyser Fiskeoppdrett nr 1/2002 In Survey of Profitabil ity in Production of Salmon and Trout; Norwegian Directorate of Fisheries: Bergen, 2002; 71 (summary in English) http://www.fiskeridir.no/sider/statistikk/matfisk/ matfisk01/index.html (accessed April 2003) Waagbø, R.; Torrissen, O.J.; Austreng, E Fo r og ˆ formidler den største utfordringen for vekst i norsk ˆ havbruk (Feed and feed ingredients The greatest chal lenge for growth in Norwegian aquaculture); Norges forskningsrad: Oslo, Norway, 2001; 58 ˚ Austreng, E Forutnytting hos laks samanlikna med ˆ kylling, gris og sau (Feed utilization of salmon compared with chickens, pigs and sheep.) Nor Fiskeoppdrett 1994, 2A, Salmon Bromage, N.; Porter, M.; Randall, C The environmental regulation of maturation in farmed finfish with special reference to the role of photoperiod and melatonin Aquaculture 2001, 197, 63 98 Schmidt, E.B.; Christensen, J.H.; Aardestrup, I.; Madsen, T.; Riahi, S.; Hansen, V.E.; Skou, H.A Marine n fatty acids: Basic features and background Lipids 2001, 36S, 65 68 Bell, J.G.; McGhee, F.; Campbell, P.J.; Sargent, J.R Rapeseed oil as an alternative to marine fish oil in diets of post smolt Atlantic salmon (Salmo salar): Changes in flesh fatty acid composition and effectiveness of subsequent fish oil ‘‘wash out.’’ Aquaculture 2003, 218, 515 528 Gjedrem, T Genetic improvement of cold water fish species Aquacult Res 2000, 31, 25 33 10 Gjerde, B.; Simianer, H.; Refstie, T Estimates of genetic and phenotypic parameters for body weight, growth rate and sexual maturity in Atlantic salmon Livest Prod Sci 1994, 38, 133 143 11 Gjerde, B.; Rye, M Design of Breeding Programs in Aquaculture Species Possibilities and Constraints In Genetics and Breeding of Mediterranean Aquaculture Species; Proceedings of the Seminar of the CIHEAM Network on Technology of Aquaculture in the Mediterra nean (TECAM), Zaragoza, Spain, 1997; Vol 34, 181 192 Options Mediterr 12 Hoyheim, B Genetic Mapping in Salmonids, an Overview of the Current Research in Atlantic Salmon, Rainbow Trout and Brown Trout Proceedings of the EMBO Workshop on Reproduction & Early Development, Bergen, Norway, Oct 7, 1998; University of Bergen: Bergen, 1998 Selection: Marker Assisted R Mark Thallman U.S Meat Animal Research Center, Clay Center, Nebraska, U.S.A INTRODUCTION Marker-assisted selection (MAS) is the process of using the results of deoxyribonucleic acid (DNA) tests to assist in the selection of individuals to become the parents in the next generation of a genetic improvement program The term marker refers to a location in the genome at which a specific difference in DNA sequence has been associated with an effect on the trait of interest The word assisted implies that the selection is also influenced by other sources of information, such as phenotypes (observed or measured value) of the individuals and, in many cases, phenotypes of relatives of the individuals (which requires pedigree information) Selection methods based only on phenotypes (and optionally) pedigree will be referred to as traditional methods of selection The additional information provided by the DNA test results should improve the accuracy of evaluating the genetic merit of the individuals in the population, and hence, should improve the rate of response to selection ADVANTAGES OF MARKER-ASSISTED SELECTION Traditional methods of selection can produce very accurate evaluations of genetic merit for traits that are high in heritability (observed or measured value is a good predictor of breeding value) or for individuals that have many progeny with phenotypes recorded However, many traits of economic importance in livestock are low or moderate (10 40%) in heritability or can only be measured postmortem, in which case, accurate genetic evaluations are only possible through progeny testing Other important traits can only be measured late in the productive life of the individual For these traits, accurate genetic evaluations can only be obtained after the selection decision (to produce progeny) has been made These are the traits for which MAS is expected to accelerate the rate of genetic improvement[1,2] because the DNA testing component of MAS can be obtained and combined with marker-adjusted estimates of the parents’ breeding values anytime after birth In theory, it is possible to apply DNA testing to a few cells of an embryo Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019791 Copyright D 2005 by Marcel Dekker, Inc All rights reserved and use MAS to determine whether to transfer the embryo and even to shorten the generation interval by combining MAS with germ-line manipulation.[3] DNA tests can increase the amount of information provided by each phenotype collected, and thus, reduce the number of phenotypes required, but they not eliminate the need for phenotypes Marker-assisted selection has the potential to reduce the impact of antagonistic genetic correlations by concentrating selection intensity on those genes that affect one set of traits without undesirable effects on other traits.[1] CATEGORIES OF DNA TESTS DNA tests that could be considered for use in a MAS program can be grouped into the following general categories: functional tests, association tests, and linked marker tests Functional tests are those in which a polymorphism (difference in DNA sequence) being tested is the cause of an associated phenotypic difference These tests are the easiest to apply in a breeding program, but they are also the most expensive to develop However, a gene can have several functional polymorphisms, but the test will detect only those that it is specifically designed to detect, which implies that they are known The process of searching a population for all of the relevant functional polymorphisms in a gene is expensive and difficult Therefore, it should not be assumed that a functional test will account for all of the genetic variation in a particular gene Association tests are based on population-wide coinheritance (assumed to be due to linkage disequilibrium) of the markers being tested and the gene affecting the phenotypes As this association may differ among breeds, the relationship within each breed in which the test will be used needs to be established, and this requires phenotypes and DNA tests on a substantial number of animals from each breed Initially, it is likely that the associations will be established in mixed populations, representing the breeds of primary importance In such cases, it is very important that breed differences are accounted for in the analysis; otherwise, spurious or biased associations between DNA tests and traits are likely to occur It is 781 782 likely that initially, association tests will be the most widely used category of tests for production traits in livestock Association tests are likely to eventually be converted into functional tests over time, but this is an expensive and time-consuming process As a practical matter, it may be very difficult to determine whether a particular difference in DNA sequence is causative of phenotypic differences, or is merely associated with the differences; thus, it may not always be clear whether a particular test is a functional or an association test However, it is not necessary to know which of these two categories a particular test belongs to because the way in which they are used is very similar Linked marker tests are based on the cosegregation of DNA markers and phenotypes within families Thus, the linkage phase (the association between the markers being tested and the gene affecting the phenotypes) must be established within each family in which the markers are to be used for selection Consequently, DNA tests must be performed on progeny with phenotypes within each family This is the primary factor limiting the application of linked markers Consequently, they are best suited to within-herd use by large breeding companies Linked markers have the advantage of being the easiest and least expensive to develop Most published QTL are currently defined by linked markers Over time, many of these will be converted to association tests, and eventually, to functional tests INTEGRATION OF DNA TESTING WITH GENETIC EVALUATION SCHEMES Quantitative traits (which include most production traits in livestock) are generally assumed to be influenced by a few genes with moderate or large effect and a greater number of genes of smaller effect DNA tests are currently only available for a few of the genes with moderate or large effect The aggregate effect of the remaining genes is referred to as the residual polygenic breeding value,[4] which will often account for a very substantial proportion of the genetic variance for a trait Furthermore, with multiple genes affecting each trait and multiple traits affected by most genes, optimizing the relative selection pressure to apply to each DNA test and the residual polygenic component is not a trivial task The most efficient way to integrate the various sources of information is a combined analysis The marker-adjusted estimated breeding value (MAEBV) for a trait is the sum of an estimated effect of each DNA test in the analysis plus the estimated residual polygenic breeding value Although the application of MAEBV is in its infancy, the concept is not new.[2,5] Selection: Marker Assisted It may be tempting to try to adjust traditional estimated breeding values (EBVs) for DNA test results However, if a sire has a large number of progeny with phenotypes, the accuracy of his traditional EBV will be high and it will not differ substantially from his MAEBV because his total genetic merit is already well established and the DNA tests only provide information about which genes contributed to his total merit On the other hand, a set of young sires (without progeny or phenotypes) that are candidates for progeny testing would have low-accuracy EBVs that are simply the averages of their parents’ EBVs; their MAEBVs could differ substantially from their traditional EBVs The extent to which an EBV differs from a MAEBV depends on a number of factors, so the computation of MAEBVs is best done in a genetic evaluation system that considers all relevant sources of information simultaneously DETERMINING WHICH DNA TESTS TO USE IN MAS Commercial availability of a substantial number of DNA tests is a prerequisite for MAS to have a major impact on livestock breeding However, this variety of tests implies that breeders, breed associations, and organizations that conduct genetic evaluations must decide which DNA tests are most profitable or productive for inclusion in their respective genetic improvement programs Factors that should be considered in the decision are: amount of evidence that the effect of the test is real (not a statistical artifact), the magnitude of the effect, the frequencies of the major alleles, the percentage of genetic variation accounted for by the test, and the degree of dominance Together, these factors determine the potential for genetic improvement and the rate at which that improvement could occur Ideally, the above information would be estimated from animals of the breed(s) in which the test would be applied Effects on all available traits should be reported It is unlikely that a gene would affect only one trait, in spite of the current trend to label commercial DNA tests as being associated with only one trait REALISTIC EXPECTATIONS DNA testing is not likely to make animal breeding simpler, as was initially expected, but it should make selection more effective DNA tests are likely to change (improve) over time As more data is acquired, estimates of the effects of test genotypes will improve Furthermore, the Selection: Marker Assisted association between test and functional polymorphisms is likely to be different between breeds, but these differences are likely to be discovered only after a large amount of data has been generated by using the tests widely for a number of years To get started, the only practical approach is likely to be to use species-wide associations Cost will limit the adoption of DNA testing in livestock, although costs are projected to decrease substantially over the next few years CONCLUSION The adoption of MAS in the livestock industries has been much slower than many would have predicted 10 to 15 years ago However, there are several examples of application of MAS in commercial livestock populations.[6,7] Commercial DNA tests for quantitative traits are on the market for several species and MAS has the potential to substantially increase response to selection As more tests become available over the next few years, it seems likely that MAS will become increasingly important in livestock breeding 783 REFERENCES Weller, J.I Quantitative Trait Loci Analysis in Animals; CABI Publishing: Wallingford, UK, 2001; 217 242 Smith, C Improvement of metric traits through specific genetic loci Anim Prod 1967, 9, 349 358 Georges, M.; Massey, J.M Velogenetics, or the synergistic use of marker assisted selection and germ line manipulation Theriogenology 1991, 35, 151 159 Soller, M The use of loci associated with quantitative effects in dairy cattle improvement Anim Prod 1978, 27, 133 139 Fernando, R.L.; Grossman, M Marker assisted selection using best linear unbiased prediction Genet Sel Evol 1989, 21, 467 477 Spelman, R.J Utilization of Molecular Information in Dairy Cattle Breeding Proceedings of the 7th World Congress on Genetics Applied to Livestock Production, Montpellier, France, Aug 19 23, 2002; 2002 CD Rom Communication No 22:02 Boichard, D.; Fritz, S.; Rossignol, M.N.; Boscher, M.Y.; Malafosse, A.; Colleau, J.J Implementation of Marker Assisted Selection in French Dairy Cattle Proceedings of the 7th World Congress on Genetics Applied to Livestock Production, Montpellier, France, Aug 19 23, 2002; 2002 CD Rom Communication No 22:03 Selection: Traditional Methods Lawrence R Schaeffer University of Guelph, Guelph, Ontario, Canada INTRODUCTION Selection is defined as any human manipulation that restricts the mating of animals such that each animal does not have an equal chance of reproducing Only animals that reproduce influence the genetic composition of the next generation The purpose of selection is to change the genetic composition of a livestock population to have more animals with desired characteristics INFINITESIMAL MODEL Traditional selection methods have assumed that performance traits are controlled by an infinite number of gene loci, each with an equal-sized contribution to the trait of interest Only purely additive gene action has been assumed to exist, i.e., the genetic effects that are passed to progeny Dominance effects and other interactions between loci have been assumed to be negligible.[1] can be much higher Intensity of selection is a function of reproductive output compared to the number of males and females for creating the next generation The generation intervals for males and females could be different depending on when selection decisions are made for each sex In dairy cattle, for example, sires are not culled until their first daughters have matured, calved, and completed a full lactation of milking Thus, sires can be six years of age or older Cows are often culled based on their own performance, somewhere between 20 and 36 months of age Response to selection can be increased in several ways Accuracy of evaluation can be increased by using more data and better methods of evaluation Intensities of selection can be increased by selecting fewer animals from among the possible candidates Generation intervals can be shortened by making selection decisions sooner in an animal’s life All of these factors must be balanced against the costs of achieving them TYPES OF SELECTION ELEMENTS OF GENETIC CHANGE The amount of genetic change caused by selection depends on several factors The key equation[2] to predict response to selection, R, is R ẳ rm im s ỵ rf if s L m ỵ Lf Selection is based on different sources of information The trait often determines the type of selection that can be applied For example, not all traits are expressed in both sexes, such as milk production in dairy cattle, or litter size in swine and rabbits Sex-limited traits require selection based on progeny information An Animal’s Own Performance where rm and rf are the accuracies of evaluating the genetic merit of male and female animals, respectively; im and if are the intensities of selection (e.g., the top 5%) for males and females, respectively; s is the genetic variability in the population; and Lm and Lf are the generation intervals for males and females, respectively A generation interval is the average age of a male or female parent when a progeny of that individual can replace it in the breeding population under a particular testing scheme (Table 1) In many livestock species, males can have larger progeny groups than females Consequently, males can be more accurately evaluated from their more numerous progeny than females Because fewer males are needed for matings than females, the intensity of selection on males 784 Animals were originally selected on the basis of their own phenotype That is, cows that give the most milk, sows that have the largest litters, hens that lay the most eggs, and horses that run the fastest are examples of this type of selection Although selection on phenotypes is very easy to apply, the accuracy of phenotypes as an estimate of genetic merit is equal to the square root of heritability Heritability is the proportion of the variability in a trait that is attributable to genetics (Table 2) For most economically important traits, heritability ranges from 0.05 to 0.50 Consequently, response to selection on an animal’s own performance may not be very high Accuracy can be improved slightly for some traits by averaging several observations taken on the same animal Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019792 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Selection: Traditional Methods 785 Table Minimum possible and typical generation intervals for common livestock speciesa Species Sexual maturity Gestation length Minimum possible Typical males Typical females Offspring per gestation Cattle (Bos taurus) Horses Swine Sheep Goats Rabbits Chickens Turkey Rainbow trout 12 mo 15 24 mo 120 250 d 185 d 165 d 125 d 140 d 224 d yr 280 d 340 d 112 d 150 d 150 d 31 d In egg In egg In egg 33 mo 41 59 mo 19 20 mo 17 mo 15 16 mo 11 mo 11 mo 15 16 mo yr yr 12 yr 1.5 yr yr yr yr 1.5 yr 1.5 yr yr yr 12 yr 1.5 yr yr yr yr 1.5 yr 1.5 yr yr 1 10 12 2 12 250 100 1,000 a Values may vary with breed within species Progeny Performance For sex-limited traits, the average performance of an animal’s progeny can be used Males can generally have many dozens or hundreds of progeny and the accuracy of evaluating the genetic merit of that male can approach 100% A disadvantage is that one has to wait until the progeny are born, grow, and make their own performance records, thereby increasing the generation interval and lowering response to selection An optimal balance between accuracy of evaluation and generation interval has to be achieved Relatives’ Performance Animals’ genetic merits could be evaluated using information on parents, full-sibs, or half-sibs Accuracy of evaluation is limited by the amount of information on relatives and depends on the particular combination of relatives Animals could be evaluated before they are old enough to be used for breeding purposes The generation interval can be shortened using relatives’ records, but accuracy of evaluation may suffer Combining All Sources of Information The best method of evaluating genetic merit is through the use of an animal model.[3] An animal model is a statistical method for combining information from the animal’s own performance, all other relatives, and all progeny, and at the same time, account for any nongenetic factors that might influence performance of animals, such as contemporary groups, ages, years, and seasons Animal models make efficient use of the data and generally provide the highest probability of correctly ranking animals for genetic merit Animal models have been used in dairy, beef, and swine since 1989 in various countries around the world The methodology generally applied to the animal model is called best linear unbiased prediction, or BLUP Methodology and genetic models, however, are continually being improved EVALUATION OF MORE THAN ONE TRAIT Livestock are often evaluated for many traits, such as production, reproduction, conformation, and health Selection can be applied separately to each trait (independent culling levels), or traits may be combined into an economic index The first step is to define the breeding goal, i.e., all of the traits that the breeder hopes to change The next step is to identify the traits that will be in the economic index For example, there could be five traits in the breeding goal, and 12 traits in the economic index Traits in the breeding goal may not be measurable directly on animals, and so two or three other correlated traits are used in the economic index as indicators of the trait in the breeding goal The genetic variability of each trait, in the breeding goal and in the index, must be known as well as the genetic correlations between all traits A genetic correlation between two traits is an estimate of the proportion of genes that influence both traits Relative economic weights can be computed Table Heritabilities of different kinds of traits Low (0 0.15) Litter size Fertility Disease susceptibility Locomotion Conception rate Longevity/ survival Medium (0.15 0.40) High (0.40 0.70) Milk production Growth traits Feed efficiency Carcass traits Meat tenderness Meat yields Body lengths Racing speed Egg production Milk components Gaits Fleece weights 786 from figures on costs and returns using the estimated genetic correlations and genetic variabilities of traits Selection on an economic index leads to optimum change in economic value over all traits Often, one trait has greater economic importance than the other traits, and so relative economic values are often debated Economic indexes may be derived in many different ways For example, the weights for the index may be based on the desired responses that the user seeks for each trait Or, one or more traits, perhaps, should not change either for the better or worse, and weights can be derived to accomplish this goal Some traits are related to each other, or to economics in a nonlinear manner For example, legs on animals can be either too straight or too curved, but both lead to economic losses compared to an animal with desirable legs between too straight and too curved Thus, economic indexes can be nonlinear functions CONSEQUENCES OF SELECTION Selection changes the frequencies of genes that affect the traits of interest.[1] Frequency changes can raise or lower the means of traits and also increase or decrease the genetic variability of traits Genes may affect more than one trait, directly or indirectly, so that selection will directly affect the traits of interest and will indirectly affect many other traits (i.e., correlated responses) that may not be observed in traditional record keeping For example, many years of selection for increased milk yields in dairy cattle have caused a correlated decrease in reproductive performance There could also have been changes in immune responses and other traits that were not observed or recorded while selection was applied to milk production Selection tends to choose animals that are related (because they share the same favorable genes) Breeding related animals leads to an animal that may have the same gene allele on both chromosomes This is called homozygosity The proportion of gene loci in an individual that are homozygous is an inbreeding coefficient Greater homozygosity results in lower genetic variability Inbreeding can decrease performance and increase the likelihood of undesirable genes becoming homozygous, which could result in death or greater susceptibility to diseases Mating programs can be designed to maximize the ratio of selection response to level of inbreeding, or to minimize the increase in inbreeding per generation Such programs dictate which males should be mated to particular females EFFECTIVENESS OF SELECTION Traditional selection methods have provided rates of genetic response up to 3% of the mean per year, depending Selection: Traditional Methods on species and trait.[4] Genetic responses are cumulative and can become appreciable over time Expected genetic responses are often not realized because of changing economic situations that force producers to change their breeding objectives Genetic change has been most noticeable in species with short generation intervals such as poultry and swine Broiler chickens reach market weights significantly earlier on less feed than they did just 20 years ago, for example Genetic responses in dairy cattle for production traits have been significant due to the ability to pick the best males on an international basis rather than within country CONCLUSION Future selection programs will be improved versions of the traditional selection methods Knowledge about individual genes, their location, the proteins they produce, and the metabolic pathways that they control will be incorporated into genetic evaluation models and will be used to shorten generation intervals such that genetic response is increased More traits will be included in the breeding objectives so that unwanted correlated responses can be avoided The pedigree and data files that have been created over the decades will become more valuable in discovering major quantitative trait loci (QTL) Application of DNA tests to embryos could perhaps more accurately identify superior animals and at the same time greatly shorten the generation interval Care should be taken to completely understand the functions of individual genes because these might influence other genes in an antagonistic manner, thereby nullifying any benefits of selection using that gene Breeders of animals will continue to select the best animals, mate the best to the best, and strive to improve livestock to near genetic perfection REFERENCES Falconer, D.S.; Mackay, T.F.C Introduction to Quantita tive Genetics, 4th Ed.; Longman Group Ltd: Essex, U.K., 1996 Bourdon, R.M Understanding Animal Breeding; Prentice Hall, Inc.: New Jersey, 1997 Henderson, C.R Applications of Linear Models in Animal Breeding; University of Guelph: Canada, 1984 Smith, C Introduction: Current Animal Breeding In Animal Breeding Technology for the 21st Century; Clark, A.J., Ed.; Harwood Academic Publishers: Amsterdam, 1998; 10 822 Swine: Breeding and Genetics Table Relative importance of reproduction and production traits Relative importancea Trait Reproduction Production a b Age at puberty Conception rate Number born alive / litter Piglet viability Total Growth rate Food conversion Carcass yield Lean percent Total 14 48 32 100 15 23 16 46 100 36 34 27 100 38 20 12 30 100 a Profit function (France) b Return per slaughter pig (The Netherlands) a Relative increase (%) in profitability from an increase of one phenotypic standard deviation of each trait (Adapted from Ref 8.) male and female candidates, termed criteria of selection These two sets of traits only partly coincide, and each set includes a fairly large number of traits Performance recording programs define the measurements to be used as selection criteria Reproduction performances are assessed through onfarm litter-recording systems, including litter size at birth and at weaning, and sometimes litter weights Production traits, namely growth rate, feed efficiency, and carcass measurements, were initially recorded in central testing stations, built on the Danish model An important step has been the advent of techniques allowing a fairly accurate evaluation of body composition by measuring fatness on the live pig.[4] This has opened the road to central performance testing stations of young boars, and to onfarm testing programs More recently, meat quality traits measured in slaughterhouses have been introduced into testing programs Pig improvement is essentially a multiple-trait selection problem, which is solved by combining performance records into an index (I) This index is a predictor of breeding value, chosen so as to maximize the correlation between I and the aggregate genotype H.[2] Eventually, selection index theory came to include methodologies accounting for unequal information among candidates and nongenetic effects and providing best linear unbiased predictions (BLUP) of breeding values THE DESIGN OF BREEDING PROGRAMS Selection response depends on three parameters, i.e., selection accuracy (r, correlation between the aggregate genotype and the selection criterion), selection intensity (i, standardized selection differential), and generation interval (t, usually measured in years) The expected annual response, expressed in genetic standard deviation units, is Ra ¼ i1 r1 ỵ i2 r2 ị=t1 ỵ t2 ị where the indices and refer to dams and sires, respectively An efficient breeding program thus depends on a proper choice of evaluation methods (maximizing r) and replacement policies (maximizing i and minimizing t) Production traits in pigs are measurable on both sexes either before breeding (growth rate, food conversion, and fatness), which permits individual selection, or after slaughter (lean content, lean and fat tissue characteristics), which permits only family selection The maximum expected annual response is nearly one genetic standard deviation with individual selection for production traits With the advent of BLUP, records from relatives such as siblings, cousins, and ancestors are used to predict breeding values with greater accuracy, and better acrossfarm (or -station) evaluations are also achieved Overall, Table Relative weights of reproduction (H1) and production (H2) traits to accommodate four breeding systems using three different breeds Breed Breeding system (dam  sire) Pure breeding Single cross Back cross Three way cross Number of lines (or breeding A  A or B  B or C  C AÂC (A  B)  B (A  B)  C objectives) per breed a Economic weight of H1 relative to H2 in a pure breeding system (Adapted from Ref 8.) A aH1+ H2 aH1+ 0.5H2 aH1 + 0.5H2 aH1 + 0.5H2 B aH1+ H2 aH1 + 1.5H2 aH1 + 0.5H2 C aH1+ H2 H2 H2 Swine: Breeding and Genetics the advantage of BLUP over individual selection in genetic response has been shown to be in a range of 10 30% for most production traits As shown in Table 2, reproduction traits should also be included in the breeding objectives Though most studies have so far concluded that reproduction is genetically uncorrelated with production, there are indications that this might not be a general rule, which would tend to make selection for reproduction traits increasingly worthwhile MARKER-ASSISTED BREEDING Advances in molecular genetics have generated genetic maps showing highly polymorphic markers evenly spaced over the 19 chromosomes of the species.[5] Consequently, the role that individual gene or marker identifications can play in breeding schemes is enhanced, compared to classical quantitative genetics methods relying only on measurements of performances.[6] For single-locus traits, the objective is to change gene frequency at the locus of interest by selecting the gene itself (when possible) together with nearby marker loci, a process termed marker-assisted selection (MAS) The process depends on the marker loci hitchhiking the genes of interest This procedure has been illustrated in the elimination of the deleterious halothane gene from maternal lines, achieved in the 1980s by using biochemical markers The pig linkage map offers several similar possibilities Major genes for meat quality and resistance to disease are areas of particular interest Polygenic traits are under the control of quantitative trait loci (QTL) and the environment Several QTL have been mapped[7] and may be exploited in selection When all sources of gain are cumulated, considerable increases in responses may be expected from MAS.[8] This implies that the relevant QTL can be hitchhiked by the markers, as in the single-locus case examined earlier In situations of statistical independence among loci, marker QTL associations can be detected only within families, and lower gains in selection accuracy are obtained The gains then result from more exact coancestry for segments of the genome including QTL.[9] CONCLUSION The efficiency of pig breeding programs is reflected in genetic gains reported for growth and body composition 823 on the order of 0.5 1.5% of the mean annually.[1] No change of appreciable magnitude had been reported for litter size at birth up to a recent past in most countries, though appreciable genetic gains in piglets born per litter have recently been reported Further opportunities will arise from knowledge accumulated on classical, quantitative, and molecular genetics.[10] Specific challenges have to be faced for quality of lean and fat tissue or disease resistance A better knowledge of the genome and the identification of genetic markers and functional genes are expected to complement conventional breeding plans Pig breeding will continue to rely basically on the optimal exploitation of the pig reproductive capacity, the efficient use of breeding value evaluation tools, and an adequate management of genetic variability A well-balanced approach will remain essential in future genetic improvement schemes REFERENCES 10 Sellier, P.; Rothschild, M.F Breed Identification and Development in Pigs In Genetic Resources of Pig, Sheep and Goat; Maijala, K., Ed.; World Animal Science; Elsevier: Amsterdam, 1991; Vol 12, 125 143 Hazel, L.N The genetic basis for constructing selection indexes Genetics 1943, 28, 476 490 Smith, C The use of specialised sire and dam lines in selection for meat production Anim Prod 1964, 6, 337 344 Hazel, L.N.; Kline, E.A Mechanical measurement of fatness and carcass value on live hogs J Anim Sci 1952, 11, 318 Archibald, A.L.; Haley, C.S Genetic Linkage Maps In The Genetics of the Pig; Rothschild, M.F., Ruvinsky, A., Eds.; CAB International: Wallingford, UK, 1998; 265 294 Neimann Sorensen, A.; Robertson, A The association between blood groups and several production character istics in three Danish cattle breeds Acta Agric Scand 1961, 11, 163 196 Bidanel, J.P.; Rothschild, M.F Current status of quantita tive trait locus mapping in pigs Pig News and Information 2002, 23 (2), 39N 54N Ollivier, L Genetic Improvement of the Pig In The Genetics of the Pig; Rothschild, M.F., Ruvinsky, A., Eds.; CAB International: Wallingford, UK, 1998; 511 540 Fernando, R.L.; Grossman, M Marker assisted selection using best linear unbiased prediction Genet Sel Evol 1989, 21, 467 477 Rothschild, M.F.; Ruvinsky, A The Genetics of the Pig; CAB International: Wallingford, UK, 1998 Swine: Health Management John Carr Iowa State University, Ames, Iowa, U.S.A INTRODUCTION The clinical appearance of many diseases and disorders of farmed pigs is heavily influenced by the pigs’ environment The classical concept ‘‘pathogen meets pig results in clinical disease’’ is nearly always incorrect The pig industry and its servicing veterinary advisors have moved from individual animal medicine through preventive medicine into health maintenance All of the skills learned previously still need to be employed, but veterinarians are now required to apply a degree of animal science knowledge for which they are rarely prepared THE PIG CLINICIAN AND HEALTH TEAM To maintain the health of swine, the clinician needs to approach the pig unit with regard to six major areas: 1) biosecurity; 2) pig flow; 3) medicine management; 4) review of current stock health and susceptibilities; 5) competency of the stockpeople; and 6) the provision of an environment conducive to healthy pigs Managing the health of pigs on a farm must become the responsibility of a farm health team, which includes a veterinarian However, the key players are the stockpeople If their training is inadequate, disease recognition will be delayed, with potentially devastating consequences for both the pigs involved and the farm, and even nationally This was classically demonstrated by the 2001 foot-and-mouth disease (FMD) outbreak in the United Kingdom, where failure of the producer to recognize and report clinical signs of FMD in his pigs to his local veterinarian resulted in the unnecessary deaths of million animals to control the disease.[1] BIOSECURITY Biosecurity is a major responsibility of the farm health team, and awareness of the ease of disease spread is required for all members of the team It is impossible (at present) to prevent the transmission of some diseases, for example, various serotypes of Escherichia coli or earthborne pathogens such as Erysipelothrix rhusiopathiae Some diseases may spread long distances through the air, 824 for example, parvovirus Other pathogens are only locally spread Mycoplasma hyopneumoniae, for example, will affect farms within a 3-km zone However, for farms located in an area of low farm density, maintenance of a M hyopneumoniae-free status has been possible for more than 20 years.[2] Some diseases, such as Sarcopties scabiei var suis, require direct pig contact With modern avermectin therapies, eradication of mange on pig farms is achievable Adequate biosecurity is the responsibility of the entire pork production chain, from the nucleus and multiplication farms, with their artificial insemination (AI) studs, to the family farm A pathogen that is absent from the farm or area, such as pseudorabies (Aujeszky’s diseases), does not require treatment or prevention Indeed, the absence of pathogens allows for more errors in environmental management before production suffers PIG FLOW The lack of animal science understanding by the veterinary profession has allowed farms to grow without regard for the biology of farmed pigs Producers are driven by the need for an economic return and by the constraints of buildings and local legislation Veterinarians and producers have turned to antimicrobials to balance pathogen load against health and disease Over time, with inadequate cleaning, environments become infected with an increasing number and variety of pathogens Eventually, the disease challenge overwhelms the natural defense mechanisms and increasing numbers of pigs present with clinical disease The easiest way to control the pathogen load is to move clean pigs into new buildings This is clearly impossible in a farm environment, but an approximation can be reached by adopting strict all-in/ all-out procedures combined with single-source policies All-in/all-out is poorly understood by the farming community The keystone must be pig flow The provision of the pigs of the same age and health status is achieved only by minimizing the variation in pig numbers produced per batch by no more than 15% overall 5% below target output and, equally important, no more than 10% above target output This creates stable farms and helps to reduce greed in procedures In several parts of the world, legislation regarding stocking density, as in the European Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019811 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Swine: Health Management 825 Union,[3] is forcing farmers to adopt pig flow measures, because failure will result in fines and other penalties Pig flow is a complex concept that prescribes the number of animals the farm can accommodate and then models a production method to fill these buildings.[4] The area where pig flow fails on most farms is the gilt pool; having insufficient gilts results in a reduction in output Poor management of the gilt pool results in a glut of gilts in estrus, resulting in overproduction and overstocking of the facilities (Fig 1) MEDICINE MANAGEMENT Medicine storage and usage are the cornerstone of any preventive medicine program The diagnosis of increased coughing and mortality in finishing pigs, associated with swine influenza virus or M hyopneumoniane, may result from the freezing of vaccines in the farm, veterinarian, or distributor’s refrigerator A study of farm medicine storage areas revealed that 10% of farms stored their vaccines below 0°C.[5] The inappropriate use and overuse of needles and syringes have been demonstrated in the transmission of many pig pathogens, including porcine reproductive and respiratory syndrome virus and classical swine fever virus (Fig 2) STOCK HEALTH The ability to clinically examine, recognize, and treat disease in pigs is the responsibility of the entire farm Fig Vaccines stored in a freezing refrigerator on a farm where pigs experience finishing pneumonia, despite vaccination health team Adequate training of stockpeople in the recognition of disease is a responsibility of the farm’s attending veterinarian Continual professional development is a prerequisite for the veterinarian as new diseases (postweaning multisystematic syndrome) appear and established diseases (Glasser’s disease) evolve in the modern pig industry The pig itself carries the ability to succumb to or fight disease agents As the pig’s genetic makeup becomes more understood, commercially available resistance factors will include more than just Escherichia coli F4 or F18 resistance.[6] A major problem in pig health management is compromised or sick pigs, who are the major sources of disease pathogens It is essential that farms provide hospital accommodations and suitable treatment regimes to provide for these pigs STOCKPERSON AND STOCKMANSHIP Fig Pig flow model for a 20 sows per week farm The fulcrum around which pig health resolves is the stockperson’s abilities Modern pig farming has a greater reliance on employed help, who may have little interest in the well-being of the pig The National Pork Board’s Swine Welfare Assurance Program initiative[7] concentrates on the pig’s behavior toward the stockpeople A caring environment promotes good health and productivity.[8] 826 ENVIRONMENTAL MANAGEMENT The expression of clinical production diseases is often determined by the environmental stressors to which the pigs are subjected Assessment of the environment can be easily achieved when the environment is broken down into its component parts: the water supply, the feeding system, the flooring, and the air (Fig 3) Water Supply A supply of fresh drinking water is essential to pig health A drinker that provides water is generally accepted as good enough by untrained stockpeople However, the flow may be inadequate, the drinker’s height inappropriate, the drinker type unsuitable, the water contaminated, or the drinker affected by stray voltage If these factors are not recognized and corrected by the stockpeople, then performance and pig health will be negatively affected Swine: Health Management aerosolized during feed distribution This can impact the health of both stock and stockpeople Flooring Stocking densities for all stages of pigs are becoming a legal constraint on pig production throughout the world Pig health improves with increased space allowance per pig, but pork output is negatively impacted Therefore, an acceptable balance between space and production is required As farms age, flooring and other contact surfaces (walls, doorways, and passages) become eroded, particularly around feeders and water supplies Poor maintenance routines ultimately result in compromised pig health Analysis of the floor would also include hygiene The lack of all-in/all-out routines results in poor or inadequate cleaning routines and maintenance It is only through good pig flow that sufficient time can be set aside to allow stockpeople to adequately care for the floor Feeding System Air Growth rates are determined by the ability of pigs to eat The type of feed, presentation of feed, and hygiene of feed are factors that the farm health team needs to constantly assess to ensure that health and production are maintained In addition to swine health, feed wastage plays a key role in the profitability of swine farms, yet farms may casually waste 10% of the feed Poorly constructed feeding systems impact the quantity and type of dust that is Failure of the ventilation system is the classic reason for respiratory disease Seasonal variations put tremendous pressure on the ventilation system, which fails particularly at the turn of the seasons Managing the ventilation system requires assessment of the air variations over time with reference to the temperature, humidity, gas pollutants (NH3, CO2, CO, H2S), dust and type of endotoxins Fig Environmental management directly impacts the health of pigs The photograph shows water that is difficult to obtain, a feeder that is too short, broken flooring, and dirty fans that reduce air flow in a building All of these and other problems directly compromise pig health Swine: Health Management All buildings should be designed to provide adequate living zones for the pigs for sleeping, eating and drinking, exercise, and dunging The building engineers should ensure that the building works before and during pig occupancy When failures are discovered, they should have rational improvements that can resolve the situation Poor building orientation, particularly in cross-flow ventilation buildings, results in drafts, creating poor pig respiratory health and increased vices that necessitate tail docking to control the situation Preweaning diarrhea is often associated with drafts and chilling of the neonatal piglet CONCLUSION Swine health management maintenance requires a balance between reducing the risk of new pathogens through biosecurity; providing all-in/all-out through pig flow; requiring that medications are effective through proper use and storage; recognizing sick animals promptly; and providing excellent stockmanship and ensuring that pigs are not compromised by any failing in their environment 827 REFERENCES Gibbens, J.C.; Sharpe, C.E.; Wilesmith, J.W.; Mansley, L.M.; Michalopoulou, E.; Ryan, J.B.M.; Hudson, M Descriptive epidemiology of the 2001 foot and mouth disease epidemic in Great Britain: The first five months Vet Rec 2001, 149, 729 743 Muirhead, M.R.; Alexandra, T.J.L Managing Pig Health and the Treatment of Disease; 5M, 1997 ISBN 9530150 Commission Directive 91/630/EEC laying down minimum standards for the protection of pigs Commission Directive 2001/88/EC amending Directive 91/630/EEC Carr, J Development of pig flow models Pig Vet J 1999, 43, 38 53 Carr, J Refrigeration management Pig Vet J 1999, 43, 138 143 EdemaGuardTM; F18 + E coli Resistance Using PICmarqTM Technology: http://www.pic.com Pork Checkoff Swine Welfare Assurance ProgramTM 2003, National Pork Board Hemsworth, P.H.; Barnett, J.L The effects of aversively handling pigs, either individually or in groups, on their behaviour, growth and corticosteroids Appl Anim Behav Sci 1991, 30, 61 72 Swine: Product Marketing David Meisinger Becca Hendricks National Pork Board, Des Moines, Iowa, U.S.A INTRODUCTION Market hogs and pork products are marketed and distributed over a complex pathway to customers and consumers in the United States and overseas This article will attempt to outline some of those pathways In addition, attention will be given to consumer attitudes about pork and some of the marketing programs that address these attitudes Swine and pork marketing in the United States has historically been a commodity business Pork producers have raised commodity hogs for commodity packers who provided commodity products for commodity markets In the last few years, there has been a genuine paradigm shift in the pork industry toward production and marketing of a quality product This shift began in 1991 with a dramatic shift to a very lean, heavily muscled hog in response to consumer demands for leaner meat At the same time, the industry saw a shift to caseready products with the advent of superior packaging and packaging technology With the move toward case-ready products, there has been a lateral move toward branding, which has promoted the interest in pork quality Retailers, packers, and further processors become very interested in quality and uniformity when their name is on the product LIVE HOG AND CARCASS MARKETING There has been a significant change in the way hogs are marketed in the United States Not many years ago, most hogs were marketed through either auction markets or terminal markets Direct marketing sales of pigs directly to slaughterers was a small minority of the total marketing Today, just the reverse is true Essentially, all market hogs are sold direct, either delivered directly to the slaughter plant or delivered to a packer buying station A very small percentage of hogs are sold to terminal markets, and essentially no market hogs are sold through auction markets anymore Of those sold direct, a growing percentage are sold under some type of contract arrangement, whether a costplus contract, a window contract, or just a specific market price-based contract It is estimated that 14% of market hogs are sold on contract as opposed to 65% that are sold on the spot, which means they were sold without prior 828 negotiations Packers raised the remainder (19%) By the middle of the first decade of this century, spot sales will represent no more than 10% of market hogs This is due to a desire by both producers and packers for some degree of predictability in future hog sales.[1] Another big change that occurred is the move toward carcass marketing Not many years ago, less than 10% of all hogs were sold on a carcass merit basis Now the reciprocal is true Over 90% of market hogs are sold either on a carcass merit basis or on reputation based on measurement of previous loads, or on a combination of these factors For the latter, market hogs may be measured, but are paid for on a running average of the past three loads Carcass merit is established by a multitude of methods and a number of regression equations Pork packers use a ruler to measure backfat, optical probes to measure backfat and loin depth, handheld ultrasound to measure fat and loin depth, or carcass ultrasound measurements in a sophisticated neural network of equations to estimate overall carcass lean content The packers who use optical probe technology all use different equations based on their product use to estimate percent lean in the carcass The interest in the Autofom for whole-carcass ultrasound estimation of percent lean in primal cuts has been based on future promises for the technology Autofom is sophisticated software and hardware equipment and can very accurately measure the percent lean in various cuts Packers interested in using this approach cannot currently justify the cost on the basis of paying producer suppliers more accurately, nor can they justify it on the basis of more accurate sorting and utilization of the cuts for development of different products The primary justification has been based on the future possibility of limited manpower or the increased use of robots to many of the manual disassembly procedures or fabrication procedures Pigs will never be marketed as totally uniform entities The alternative is to totally characterize the cuts so that this information can be communicated to robots that can make their movements accordingly DOMESTIC PORK PRODUCT MARKETING Some of the markets available domestically are evolving as consumers’ preferences change and as technology Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019808 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Swine: Product Marketing allows for product development Niche markets including natural pork, organic pork, welfare-friendly pork, antibiotic-free pork, or process-verified pork have become more commonplace Nutraceutical uses of pork to satisfy certain nutritional needs are also receiving more attention Fresh pork enhanced with a solution of ingredients designed to improve the tenderness, juiciness, and flavor of pork has become well accepted in the industry Over half of all fresh pork is enhanced, and consumers have come to expect the flavor and tenderness profile associated with this technology Channel marketing of fresh pork can be subdivided into retail and foodservice marketing and the distributors who deliver the product to the appropriate channel Pork is marketed about equally in the foodservice and retail markets Although pork is marketed at virtually every retail grocery store with a meat department and is usually the most profitable meat, pork cuts are typically underrepresented in the meat case According to a pork industry study, pork is more of an impulsive purchase than beef or chicken Therefore, retail pork marketing efforts should include point-of-purchase information and merchandising pieces to impact decision making at the meat case This is also important because a growing majority of pork is case-ready, and there are typically fewer instore meat cutters available to answer consumer questions about the product Lead selling items in the fresh meat case at retail have been pork chops, ribs, and roasts Because of today’s consumers’ busy lifestyles, many retailers are offering more and more convenience and precooked meat items These items are typically merchandised near the fresh product The pegboard section of the retail meat department holds the furtherprocessed products The lead selling processed items are cured hams, lunchmeats, bacon, and sausage Processed products are typically sold as fixed-weight items, and fresh products are sold as random-weight items Foodservice marketing involves sales to commercial (limited- and full-service restaurants and travel and lodging) and noncommercial (schools, institutional foodservice, and healthcare) segments These outlets are typically more interested in quality as defined by tenderness, juiciness, and flavor, and they are willing to pay for these quality assurances to guarantee repeat customers Value-added product offerings are becoming more important to operators as they face labor shortages and food safety pressures Many products being supplied to foodservice operators are now preseasoned, precooked, or preportioned by the packer or further processor who is supplying the product Over the last several years, sausage, ham, and bacon have represented over half of the products sold in foodservice outlets However, the fastest growing products have been ribs and 829 bacon Consumer trends affecting the foodservice industry include the desire for variety, taste, and experience Almost half of the consumer food dollar is spent at foodservice outlets, and operators must provide a unique experience for their patrons Pork fits well into most menus as it can be prepared in a variety of ways as well as in several ethnic dishes PORK DEMAND ENHANCEMENT STRATEGIES A discussion of demand enhancement strategies in the pork industry must start with a historical perspective The National Pork Producers Council (NPPC), a checkofffunded producer group, launched its ‘‘Pork The Other White Meat1’’ campaign in 1987 to reposition pork within the meat industry Recognizing the growing popularity of poultry (consumers were appreciating its perceived nutritional benefits and versatility as highly desirable), the pork industry saw a strategic opportunity to position pork as a uniquely different entree, competing ´ with poultry white meat rather than with its traditional red meat competitor, beef It is easy to ascertain that pork is truly a white meat, because fresh pork especially in popular cuts such as pork chops is white in color after being cooked Historically, pork was produced as much for the lard as for the meat Lard was the primary fat source prior to vegetable oils and was used for cooking, as well as for munitions and other industrial purposes The entire basis for calling attention to pork as ‘‘The Other White Meat’’ is to inform consumers that selected cuts of fresh pork are surprisingly lean, versatile, and convenient, and that fresh pork does fit into every diet Given these attributes, pork does compare favorably to other white meat products So the concept, program, and campaign that developed not only spoke to pork’s white characteristics, but also emphasized its other features that favorably position pork as a delicious break from the meal routine The campaign educated consumers that pork offers something different It was a significant multiple-year effort aimed at helping to expand domestic and export demand for pork and to lead the industry forward For more than a decade, the National Pork Board (NPB, previously the National Pork Producers Council) has remained focused and committed to the position Today, out of 10 people recognize pork as ‘‘The Other White Meat.’’ In addition, in a recent study of the most memorable contemporary advertising campaigns undertaken by the Northwestern University Graduate School of Integrated Marketing Communications, ‘‘Pork The Other White Meat’’ ranked in the top five most memorable advertising slogans in America Not only are consumers 830 Swine: Product Marketing more aware of the marketing campaign, but they rate pork 23% higher in product favorability than they did in 1994, according to an industry study The retail value of pork has steadily grown, outpacing the rate of inflation Production has increased 37% The following tables illustrate both the historical perceptions of pork (in the 1980s) and certain misconceptions that persist today In the mid 1980s, pork was falling off the map: 15 years of decline More than 10% erosion in market share Seen as being too high in cholesterol, calories, and fat A tired, dated image Not featured or promoted by key gatekeepers retail, restaurants, and the press ‘‘Second class citizen’’ Perception versus reality: Perception: Pork is high in calories Pork is high in fat Pork is high in cholesterol Pork is not nutritious Reality: Pork has 198 calories per oz serving oz of cooked lean pork has grams of fat oz of pork loin contains roughly 76 milligrams of cholesterol, which is 26% of the daily allowance serving contains one half the adult daily allowance of adult protein Pork has 50% more iron than chicken is a primary source of thiamin is high in riboflavin, zinc, and Vitamin B6 The National Pork Board continues to take the leadership in demand enhancement for fresh pork through its innovative approaches to retail, foodservice, and consumer communications In addition to the heralded ‘‘Pork The Other White Meat’’ promotion success story, the NPB has retail and foodservice merchandisers working to get pork a greater share of the meat case and a place on more menus INTERNATIONAL PORK PRODUCT MARKETING 1976 Today, USMEF has over $7 million committed specifically to promote U.S pork worldwide Some of these funds are used for traditional promotions (in-store retail promotions, menu promotions, seminars), while other funds are used to address market access issues and for research to determine market conditions for American pork products Some funds are also used for administrative support for these promotions As a result of this decades-long commitment to U.S pork, exports have risen from 142,000 metric tons in 1980 to 728,500 metric tons in 2002 Meanwhile, the value of U.S pork exports has jumped from $233 million in 1980 to $1.5 billion in 2002 Up until 1991, the United States was a net importer of pork Since then, exports have grown steadily and now represent a greater percentage of total pork production than imports Every year, record exports are recorded and now represent over 8% of total pork production This change has come about only because of a concerted commitment on the part of the U.S pork industry to provide a product that fits global customers’ needs for quality and safety The United States is also viewed as a reliable supplier, with its animal disease protection and surveillance programs in place CONCLUSION While the pork industry has seen various changes in the last several decades, it appears that structural change and the resulting changes in marketing have been accelerated Producers, as well as processors, operators, and retailers, face new issues daily, including consumer demands, food safety, product quality, product traceability, and other issues Marketing of pork and pork products in the United States and internationally is very complex and dynamic and will continue to be a major part of U.S agriculture REFERENCE The U.S Meat Export Federation (USMEF) has been conducting promotions for U.S pork since its inception in Lawrence, J.; Grimes, G Production and Marketing Characteristics of US Pork Producers; 2001; 19 National Pork Board website: www.porkboard.org Swine: Reproductive Management William L Flowers North Carolina State University, Raleigh, North Carolina, U.S.A INTRODUCTION Reproduction in swine is an integrated process that involves many events, including achievement of puberty and normal estrous cycles, fertilization, embryonic and fetal development during pregnancy, farrowing, and recovery of the sow’s reproductive system during lactation These events must occur in a coordinated sequence or the entire process fails Failures of these processes cannot be measured directly, but are reflected in reductions in farrowing rates (number of sows mated that produce piglets) and/or number of pigs born alive As a result, collection and analysis of reproductive data are key components of effective reproductive management If done correctly, it can identify problems and reproductive events that are involved, as well as suggest solutions Thus, reproductive management in swine involves three steps: 1) recognition of low performance; 2) determination of which processes failed; and 3) identification of management practices that must be changed to correct the problem(s) RECOGNITION OF LOW PERFORMANCE Identifying when reproductive performance is low requires analyses of records This is accomplished by comparing the actual level of performance within a herd with previously established production targets and decision boundaries.[1] Production targets are goals established by swine operations that represent levels of performance that are above average It is not uncommon for production targets to vary among farms, depending on genetics, geographic location, housing, and other factors When reproductive performance reaches current targets, a new set is established Therefore, the actual level of reproductive performance on a farm normally is lower than its production targets In contrast, decision boundaries are undesirable levels of performance that tend to be universally accepted within the swine industry They signify that management is negatively affecting reproduction Values above the decision boundary are interpreted as acceptable, even though they may be below the production targets Levels below the decision boundary are interpreted as being Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019814 Copyright D 2005 by Marcel Dekker, Inc All rights reserved unacceptable and indicate that immediate intervention is advisable Suggested performance targets and decision boundaries for important measures of reproductive performance are shown in Table DETERMINATION OF REPRODUCTIVE EVENTS THAT FAILED Determination of which physiological events in the reproductive process failed is accomplished by examining collectively the results from the decision boundary analyses for farrowing rate and litter size, as well as the length of time required for bred sows that not become pregnant to return to estrus The latter is referred to as the return interval Farrowing rate and litter size are classified as either acceptable or unacceptable by comparing the actual level of performance with the decision boundaries The return interval is designated as either regular or irregular, depending on when most of the nonpregnant sows exhibit estrus If it is between 18 and 25 days, then the return interval is classified as regular If it is greater than 28 days, then it is classified as irregular Five distinct patterns or combinations emerge from examination of reproductive data collectively (Table 2) The advantage of examining reproductive data collectively is that physiological events that failed can be identified (Table 2) The rationale for assigning specific events with a given pattern is based on the physiology associated with the establishment of pregnancy There are two periods during which at least embryos must be present in the uterus for pregnancy to be maintained.[2] The first period occurs between days 10 and 12 and the second between days 17 and 28.[3] If less than embryos are present during the first 12 days, the sows will not become pregnant and return to estrus 18 to 25 days after breeding (regular returns) Sows in this situation behave as if they were never mated In contrast, if there are adequate numbers of embryos on day 12, but not between days 17 and 28, the sows become pregnant, but the pregnancy ends prematurely When this happens, sows don’t return to estrus until 28 to 35 days after breeding (irregular returns) In essence, the return interval is the pivotal piece of information for determining which reproductive events are deficient for situations in which farrowing rate 831 832 Swine: Reproductive Management Table Performance targets and decision boundaries for reproductive efficiency Reproductive measure Targets > 85.0 > 11.0 < 5.0 < 1.0 Farrowing rate (%) Number of pigs born alive per litter (litter size) Number of stillborn pigs per litter (%) Number of mummified fetuses per litter (%) is poor If it is regular, then physiological events prior to day 12 failed If it is irregular, then those after day 12 were compromised Whenever both farrowing rate and numbers of pigs born alive are unacceptable, as is the case for patterns I and II, then most sows in the herd are affected The deficiency probably is part of the farm’s standard operating procedures In contrast, when farrowing rate is poor, but litter size is good, only a portion of the sows are involved Everything occurred correctly in the sows that farrowed, because litter size was normal Therefore, the deficiency is confined to a subset of sows in the herd that did not farrow The most common subsets evaluated are season (summer versus winter) and sow parity A high incidence of fetal death is a reasonable explanation for pattern III, in which farrowing rate is acceptable, but number of pigs born alive is unacceptable As a result, the numbers of mummies and stillborn pigs per litter (Table 1) are two other reproductive measures that need to be examined Mummies are partially decomposed piglets and stillborns are fully-formed, normal piglets that are born dead One or both usually will be unacceptable when farrowing rate is good, but litter size is bad If the number of mummified fetuses is high, then the problem occurred after day 50 of gestation When fetuses die, the sow attempts to reabsorb the tissue After day 50 of gestation, the fetal skeleton has been mostly calcified and decomposition involves Decision boundary < 80.0 < 10.5 > 7.5 > 1.5 primarily soft tissues The result is a mummified fetus In contrast, if the number of stillborn pigs is high, then the problem occurred during the last several weeks of pregnancy or during farrowing EVALUATION OF MANAGEMENT PRACTICES Finding management practices responsible for problems is the most time-consuming portion of reproductive management, because it involves a series of trial-and-error investigations However, knowing which reproductive events might be deficient facilitates the process by reducing the number of procedures that need evaluation Table contains a summary of management practices that should be evaluated when searching for causes The list is by no means inclusive, but it does concentrate on the most common management practices that cause failure of the physiological processes associated with reproduction Once a management practice is identified as a potential cause, corrective measures should be taken Unfortunately, it normally takes about five months to see improvements in reproductive performance This is the length of time required for sows to complete their reproductive cycle (115-day gestation, 18- to 28-day lactation, and 4- to 7-day return-to-estrus interval) As a result, subsequent analysis of reproductive performance is an important, Table Patterns of reproductive failure and their relationship to reproductive physiology Pattern Farrowing rate Return interval Number born alive Possible reproductive events that failed I Unacceptable Regular Unacceptable II III Unacceptable Acceptable Irregular N/Aa Unacceptable Unacceptable IV Unacceptable Regular Acceptable V Unacceptable Irregular Acceptable Recovery of sow reproductive tract during lactation Fertilization Embryonic development (before day 12) Embryonic development (between day 12 and 28) Fetal development (after day 28) Farrowing Recovery of sow reproductive tract during lactation Fertilization Embryonic development (before day 12) Embryonic development (between day 12 and 28) a Not applicable when farrowing rate is acceptable; then by default, the return interval is also Swine: Reproductive Management 833 Table Common management practices associated with specific patterns of reproductive failure Pattern I Reproductive event Recovery of sow Reproductive system during lactation Fertilization Management practices Embryonic development II III Embryonic development Embryonic or fetal development Farrowing IV Recovery of sow during lactation Fertilization V Embryonic mortality Embryonic mortality final step that confirms that changes in management have been effective In essence, swine reproductive management begins and ends with evaluations of reproductive data Lactation lengths less than 14 days Low nutrient intake of sows during lactation Use of low quality semen (< 70% motile and morphologically normal sperm cells) Mating frequencies of less than once per day of estrus Boar exposure (for detection of estrus) of less than 10 minutes per day P.R.R.S (Porcine Reproductive and Respiratory Syndrome) Full feeding after breeding P.R.R.S Moving or regrouping sows after breeding (days to 12) Moving or regrouping sows after breeding (days 12 to 28) Feed with mycotoxins (zearalenone or aflatoxin) Leptospirosis Parvovirus Lack of supplemental cooling when ambient temperature >80°F Average sow parities of four or greater (old sows) Inducing farrowing too early with prostaglandins Reduced feed intake during summer months Reduced feed intake in first parity sows Poor insemination or mating management by a few technicians Matings late in estrus Lack of supplemental cooling when ambient temperature is > 80°F Moving or regrouping a subset of sows after breeding (days 12 to 28) allows for the efficient identification and correction of deficiencies REFERENCES CONCLUSION Reproductive management in swine is deficient when reproductive measures fall below (or increase above) decision boundaries When deficiency occurs, immediate and decisive intervention is needed, which requires analyses of reproductive records Evaluation of farrowing rates, number of pigs born alive, and return intervals collectively result in five distinct patterns Specific reproductive events and, thus, specific management practices are associated with each pattern, which Vinson, R.A.; Muirhead, M.R Veterinary Services In Diseases of Swine, 6th Ed.; Leman, A.D., Straw, B., Glock, R.D., Mengeling, W.L., Penny, R.H.C., Scholl, E., Eds.; Iowa State University Press: Ames, 1986; 885 912 Dziuk, P.J Effect of migration, distribution and spacing of pig embryos on pregnancy and fetal survival J Reprod Fertil 1985, 48 (supplement), 57 63 Geisert, R.D.; Zavy, M.T.; Wetteman, R.P.; Biggers, B.G Length of pseudopregnancy and pattern of uterine protein release as influenced by time and duration of oestrogen administration in the pig J Reprod Fertil 1987, 79, 163 171 Swine: Waste Management Leonard S Bull North Carolina State University, Raleigh, North Carolina, U.S.A INTRODUCTION The swine industry has moved rapidly toward specialized, highly concentrated production systems and a vertically integrated business organization That trend is expected to continue not only in the United States but, as integrated companies expand offshore, the production systems developed in the United States will be replicated elsewhere Specialized, concentrated production systems in agriculture, and especially those for poultry and swine, are responsible for the high efficiency and ability to deliver consistent products at increasingly affordable prices in all markets Because concentrated production is often not located close to the cropland that is the site of feed production, which has historically served as the recipient of the animal waste for fertilizer, land application of waste has often exceeded the capacity of the crops growing on the land to assimilate the nutrients This results in the possibility of surface and groundwater contamination by the nutrients and pathogens in the waste In addition, high concentrations of animals have been associated with local concerns about emitted odors and regional concerns about emitted ammonia Swine production is substantially conducted in confinement facilities in which animals are housed in pens with slatted floors and without bedding Currently, swine waste (solid and liquid), as well as spilled drinking water and feed, drops through the slats in these floors into a pit where it is held for variable lengths of time depending on the subsequent handling system Currently used swine handling systems, new technologies, new developments, and criteria for evaluation of swine waste management systems are addressed in this article United States.[1] Lagoons are usually formed by excavation and embankment of earth to a depth of 10 feet (depending on the position of water table) and lined with compacted clay, rubberized fabric, or other impervious material (depending on the prevailing regulations) The lagoon receives the waste from the production facilities flushed by either release of large volumes of liquid recycled from the top portion of the lagoon (traditionally 800 gallons/flush/half of building, repeated two to six times daily) or release of 30,000 40,000 gallons of pit-recharged liquid and waste, approximately once weekly, from a recharge of lagoon liquid In both systems, the high flow volume and the slight slope of the waste-receiving pit under the pens (1 1.5% slope) result in effective gravity waste removal from the barns The waste streams from each of these two commonly used systems (containing less than 2% solids) may be passed through a short-retention settling basin to allow heavy solids to be retained Once the waste materials are in the lagoon, anaerobic breakdown occurs in a complex series of reactions While there is a loss of volatile materials from the lagoon surface (carbon dioxide, methane, ammonia, nitrogen gas, and other volatile compounds), most of the nutrients are retained in the organic phase as microbial cells (settled to bottom as sludge) or inorganic elements.[1] Periodically, material from the lagoon is applied to cropland as a source of nutrients, with application rate governed by the requirement for nitrogen (and, more recently, phosphorus) of that specific crop Application schedule is governed by regulations including weather and growing season Occasionally hydraulic loading rate of the application field is a limitation Deep Pit Storage Systems CURRENTLY USED SYSTEMS Flush and Anaerobic Treatment Lagoon (Flush or Pit Recharge) Anaerobic treatment lagoon systems, normally found in warmer climates where freezing is not a problem, are composed of a basin of volume range from 0.7 3.7 cubic feet per pound of animal contributing, depending on the type and age of the pig and the climatic zone within the 834 In areas where winter temperatures make liquid flush or pit-recharge systems impractical, waste is collected and stored under the slatted floors of the pens In these systems, pits of depth about feet are installed Waste is allowed to accumulate for at least months and up to 12 months, when it is pumped out and applied to the land (cropland on the same farm) Waste in these systems usually has a solid content of 6%, depending on the watering system and wastage In these systems, there is Encyclopedia of Animal Science DOI: 10.1081/E EAS 120023829 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Swine: Waste Management no supplemental storage or treatment site The pit allows some anaerobic treatment to take place While ventilation is a major consideration in all confinement operations, those with deep pits must have careful attention Ventilation is normally set to draw air downward through the slatted floor and to exit the building via fans located in the pit wall This prevents escape of potentially toxic gases from the pit into the buildings Scraper Systems While not used extensively, there are some production facilities that have scrapers under the slatted floors and that remove the waste materials in that manner using timed periodic scraping Mechanical problems, maintenance, and significant odor problems in the buildings caused by the continual mixing of urine and feces have relegated those systems to minor importance Solid Floor with Gutter and Flush In some older facilities, solid concrete floors are used without bedding, with the floor sloping slightly to the outside walls of the building At the wall area is a shallow gutter of 5-inches depth and variable width By locating the feeding and watering devices strategically, animal waste deposition is concentrated in the area of the gutter, and that which is not deposited there is worked toward the gutter by animal traffic and the slope of the floor The gutter is flushed with liquid, either recycled lagoon liquid or fresh water, in a manner similar to the flush system noted earlier but with less volume released per flush NEW TECHNOLOGIES FOR SWINE WASTE MANAGEMENT Concerns about concentration of swine production into ‘‘concentrated feeding operations’’ and possibilities of odor nuisances and extensive emissions of ammonia,[2] plus discharge of pathogens and contamination of surface and ground water with waste nutrients (especially nitrogen, phosphorus, copper, and zinc), have led to significant efforts to find economically and operationally viable alternatives to current waste management methods While traditional swine waste management involved land application of material to meet nutrient needs of crop and /or animal feed production on the same location as where the animals were raised, the move toward separation of animal production from feed production locations has changed those practices Waste management plans are now required for virtually any concentrated swine production facility that is economically viable in size These plans have, until recently, been built around 835 the requirement for available nitrogen by the crop to be fertilized by the waste In 2003, the Environmental Protection Agency revised the Clean Water Act[3] and included provision for regulation of waste application based on phosphorus as well as nitrogen That process is under development at present, but it is certain that both nitrogen and phosphorus will be used in determining the amount of all animal waste that can be land-applied The fact that many land areas that have received animal waste in the past based on nitrogen requirements have excessive levels of phosphorus poses a serious problem Many animal operations cannot comply with the combined nitrogen and phosphorus requirements with existing land area and current animal numbers The use of enzymes (especially phytase) in swine diets is becoming common, and this reduces phosphorus excretion by 40% or more This practice will greatly improve, over time, the current imbalance in soil phosphorus found on many land application sites, but the remediation time will be extensive Increased awareness of the role of animal production in atmospheric emission of ammonia is resulting in concern not only in land application of measured waste nitrogen, but also the undesirability of loss of nitrogen as ammonia to the atmosphere with deposition elsewhere Ammonia emission regulations are common in many countries already.[4] Odor emission, a local issue in animal production, is the greatest concern associated with the location of swine production facilities, and one that raises significant emotional concerns and legal challenges For that reason, swine production systems must address and significantly reduce or eliminate odor concerns beyond their property boundaries Modern swine production practices involve use of elevated levels of both zinc and copper in the diets for immunity enhancement in young pigs (zinc) and growth promotion (copper) The positive aspects of these additions result in significant reduction in need for antibiotic use The negative aspect is that these metals are excreted in the waste, which, when the waste is applied to land, can result in soil accumulations that interfere with growth of some plants NEW DEVELOPMENTS FOR WASTE MANAGEMENT In response to the need to address the waste management concerns noted earlier, many technologies have emerged that address some or all of the concerns using combinations of processing systems These include but are not limited to anaerobic digestion with energy recovery (methane), gasification with synthetic or biofuel and 836 mineral recovery, solids separation for compost development, extraction of specific fertilizer nutrients for replacement of chemical fertilizer, and water purification for recycling and reduced net usage CRITERIA FOR EVALUATION Technical evaluation of swine waste management systems considered ‘‘environmentally superior’’ includes consideration of the following performance parameters: 1) prevention of waste discharge to surface or ground water; 2) elimination of emissions of ammonia and odors to the atmosphere; 3) elimination of discharge of pathogens and disease vectors; 4) elimination of discharge of nutrients and minerals, especially heavy metals, to soil; 5) operational and economic feasibility; and 6) acceptability for permitting by local authorities A detailed discussion of a program that addresses all of these parameters under fullscale performance testing conditions is found in Ref CONCLUSIONS Swine waste management will change dramatically with the introduction of a combination of new technologies that are effective in mediating environmental concerns, pres- Swine: Waste Management sure from the industry itself to improve its position in society, and environmental regulations at federal, state, and local levels Rapid implementation of technologies that meet the above criteria will result in successful resolution of environmental issues associated with swine waste management while retaining the industry competitiveness on a global basis for human food production REFERENCES Miner, R.J.; Humenik, F.J.; Overcash, M.R Managing Livestock Wastes to Preserve Environmental Quality; Iowa State University Press: Ames, IA, 2000 National Research Council Air Emissions from Animal Feeding Operations: Current Knowledge and Future Needs; The National Academies Press: Washington, DC, 2003 United States Environmental Protection Agency Clean Water Act; 2002 www.epa.gov Battye, R.; Battye, W.; Overcash, C.; Fudge, S Develop ment and Selection of Ammonia Emission Factors; EC/R, Inc.: Durham, NC, 1994 Williams, M.C Development of Environmentally Superior Technologies: Year Three Progress Report for Technology Determinations per Agreements Between the Attorney General of North Carolina and Smithfield Foods, Premium Standard Farms, and Frontline Farmers; Raleigh, NC, 2003 www.cals,ncsu.edu/waste mgt/ ... cells much like pressing one? ?s fingertips into the side of an inflated balloon SPERMATOGENESIS Spermatogenesis progresses through three phases spermatocytogenesis, meiosis, and spermiogenesis.[1,2]... basically two types of management systems extensive and intensive with a variety of styles within each system Extensive systems are usually large sheep populations that utilize sparse forages... species present In most of the world? ?s sheep-grazing systems, the main period of pasture growth is in spring/ early summer, during which pasture usually accumulates in excess of animal requirements