Encyclopedia Of Animal Science - N ppsx

Nutrient Management: Diet Modification Terry J Klopfenstein University of Nebraska, Lincoln, Nebraska, U.S.A INTRODUCTION Animal feeding operations are becoming more concentrated and the U.S EPA (Environmental Protection Agency) has proposed more restrictive requirements Great progress has been made in diet modifications designed to reduce animal excretion of nutrients The nutrients of primary concern are nitrogen and phosphorus PHOSPHORUS UTILIZATION Phosphorus (P) is an essential mineral nutrient required for bone growth and maintenance and for most body metabolic functions such as energy utilization Phosphorus has been supplemented to animal diets in mineral form such as dicalcium phosphate produced from mined mineral deposits Typically, phosphorus was fed above the requirement of the animals as a safety factor due to lack of confidence in the precise P requirements and supplies P in manure can build up in soils and subsequently contaminate ground water if not properly managed P requirements are quite different for ruminants (cattle and sheep) and nonruminants (pigs and chickens), and P is metabolized differently by ruminants Poultry and swine grow rapidly and therefore require high levels of P in their diets (up to 6% of diet;[1–3]) Much of the P in feed ingredients (such as corn and soybean meal) is in the form of phytate P Swine and poultry lack the enzyme (phytase) necessary to utilize the phytate P so it appears in the manure Inorganic P must be supplemented to meet the animal’s requirements This makes P use very inefficient (10 to 20%) and most of the P ends up in the manure There are four technologies that producers can use to reduce P excretion Feeding to requirements Ongoing research is helping to more precisely define P requirements for each type of production and for animal ages within each type of production With modern technology, it is possible to formulate diets quite precisely so that P is not overfed.[1] Phytase This enzyme is produced commercially through microbial fermentations and can be added to 664 swine or poultry diets Phytase releases the organic P from phytate and makes it available to the animal.[4,5] Therefore, the phytate P in corn and soybeans, the primary feedstuffs in swine and poultry diets, is utilized to meet the animal’s requirements, reducing the need for supplement Phase feeding Swine and poultry grow rapidly Bone growth is very rapid in young animals and is essentially zero in mature animals Therefore, the requirement for P decreases as the animals grow and mature.[2,3] Phase feeding is the process of changing diets to reduce the amount of P In the past, two or three diets may have been fed, but now the number is increasing to five or six Phase feeding, combined with precise formulation and precise requirements, decrease dietary P and therefore manure P.[1] Low phytate feeds Genetically enhanced low-phytate corn and soybean meal are available The total P in these feedstuffs is not necessarily lower, but the P is in the available, inorganic form rather than the organic (phytate) form.[1,6] Feeding low-phytate corn and soybeans can decrease P excretion by 50% Beef and dairy cattle digest and metabolize P somewhat differently than nonruminants The microorganisms in the rumen digest the P in phytate, making the P available to the animal Beef and dairy cattle tend to grow slower and have lower P requirements than nonruminants.[7,8] Lactating dairy cows excrete considerable amounts of P in milk so cows giving milk have higher requirements higher requirements for higher producers.[8] The most important issue with ruminants is to establish precise requirements and then formulate diets to meet but not exceed requirements The requirements for lactating dairy cows is about 30% of the diet.[9] The ingredients (corn, supplemental protein, silage, alfalfa) fed to dairy cows will supply most, if not all, of this requirement Beef cattle in feedlots are typically fed diets high in corn grain, which contains 25 to 3% P Recent research suggests the requirement for feedlot cattle is 12 to 14%.[10] The problem is that the ingredients in the feedlot diets (primarily corn) have nearly 3% P There does not seem to be any practical way of reducing dietary P levels below 25% and therefore, P excretion by feedlot cattle is relatively high Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019731 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Nutrient Management: Diet Modification 665 NITROGEN UTILIZATION NITROGEN FOR RUMINANTS Nitrogen (N) is a part of amino acids (AA) that form proteins required by all animals; animals consume protein and AA and then excrete various forms of N If N in manure is not managed appropriately, it can contaminate surface and ground waters (nitrate) Just as important is the volatilization of N (NH3) from manure The resulting NH3 (ammonia) adds to odors and can be redeposited on cropland or environmentally sensitive areas such as lakes and streams Swine and poultry must be fed essential AAs to meet requirements Because of rapid lean growth, AA requirements are high and must be met to produce optimal body weight gains and feed efficiencies.[2,3] However, if any AA is fed above the requirement, that AA will be used for energy and the N excreted Cattle are unique because of the microflora in the rumen This ability allows them to digest fiber, but does raise some challenges in protein nutrition Protein that reaches the small intestine is a combination of microbial protein and undegraded feed protein This protein (metabolizable protein, MP) is digested and absorbed in a manner similar to nonruminants The growing beef animal and lactating dairy cows have two requirements that nutritionists must meet degradable protein for the rumen microbes and undegraded protein that supplies the additional MP needed by the animal.[7,8] Only recently have these requirements been elucidated, and further refinement of requirements is needed The greatest opportunity for decreasing N excretion by cattle is to use the MP system to meet but not exceed requirements for degradable and undegradable protein Phase feeding feedlot cattle and group feeding dairy cows have the potential to markedly reduce N excretion Ammonia losses have been reduced by as much as 32% by using these technologies.[13] There is some reluctance by nutritionists to reduce levels of degradable and undegradable protein because of concern that milk or beef production will be compromised Research indicates that will not happen, but it is more difficult to control variables in commercial production facilities.[14–16] IDEAL PROTEIN The ideal protein is a protein with a balance of amino acids that exactly meets an animal’s AA requirements.[11] By formulating diets to ideal protein content, no excess AAs are fed and N excretion is minimized Formulation for ideal protein can be accomplished by using highquality protein sources with good balances of AA and protein sources that complement the AA balance in corn The greatest opportunity is to use crystalline AA to balance for AA deficiencies Lowering the dietary protein content by two percentage points and supplementing with crystalline AA results in a 20 to 25% decrease in N excretion in swine or 30 to 40% in poultry.[12] CONCLUSION Phosphorus and nitrogen excretion can be reduced markedly by the use of new technologies In the future, there will be incentives for producers and nutritionists to make use of these technologies FEED ADDITIVES REFERENCES Feed additives or feeding management systems that increase feed efficiencies also increase efficiency of N utilization Ractopamine increases lean growth in swine and, therefore, increases N-use efficiency.[1] PHASE FEEDING Amino acid requirements decrease as swine and poultry grow, just as the P requirement decreases Balancing diets to ideal protein and changing diets often as pigs or poultry grow decrease the protein fed and, therefore, the N excreted.[1] Klopfenstein, T.J.; Angel, R.; Cromwell, G.L.; Erickson, G.E.; Fox, D.G.; Parsons, C.; Satter, L.D.; Sutton, A.L Animal Diet Modifications to Decrease the Potential for Nitrogen and Phosphorus Pollution; Council for Agricul tural Science and Technology: Ames, IA, 2002 CAST Issue Paper Number 21 National Research Council Nutrient Requirements of Poultry, 9th Ed.; National Academy Press: Washington, DC, 1994 National Research Council Nutrient Requirements of Swine, 10th Ed.; National Academy Press: Washington, DC, 1998 Kornegay, E.T.; Denbrow, D.M.; Yi, Z.; Ravindran, V Response of broilers to graded levels of microbial phytase 666 added to maize soybean meal based diets containing three levels of non phytate phosphorus Br J Nutr 1996, 75, 839 852 Cromwell, G.L.; Stahly, T.S.; Coffey, R.D.; Monegue, H.J.; Randolph, J.H Efficacy of phytase in improving the bioavailability of phosphorus in soybean meal and corn soybean meal diets for pigs J Anim Sci 1993, 71, 1831 1840 Cromwell, G.L.; Traylor, S.L.; White, L.A.; Xavier, E.G.; Lindemann, M.D.; Sauber, T.E.; Rice, D.W Effects of low phytate corn and low oligosaccharide, low phytate soybean meal in diets on performance, bone traits, and P excretion by growing pigs J Anim Sci 2000, 78 (Suppl 2), 72 (abstract) National Research Council Nutrient Requirements of Beef Cattle, 7th Ed.; National Academy Press: Washington, DC, 1996 National Research Council Nutrient Requirements of Dairy Cattle, 7th Ed.; National Academy Press: Wash ington, DC, 2001 Wu, Z.; Satter, L.D.; Blohowiak, A.J.; Stauffacher, R.H.; Wilson, J.H Milk production, estimated phosphorus excretion and bone characteristics of dairy cows fed different amounts of phosphorus for two or three years J Dairy Sci 2001, 84, 1738 1748 10 Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T.; Brink, D.; Orth, M.W.; Whittet, K.M Phosphorus requirement of finishing feedlot calves J Anim Sci 2002, 80, 1690 1695 Nutrient Management: Diet Modification 11 Baker, D.H.; Han, Y Ideal amino acid profile for chicks during the first three weeks posthatching Poult Sci 1994, 73, 1441 1447 12 Allee, G.; Liu, H.; Spencer, J.D.; Touchette, K.J.; Frank, J.W Effect of Reducing Dietary Protein Level and Adding Amino Acids on Performance and Nitrogen Excretion of Early Finishing Barrows In Proceeding of the American Association of Swine Veterinarians; Amer ican Association of Swine Veterinarians: Perry, PA, 2001; 527 533 13 Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T Dietary Protein Effects on Nitrogen Excretion and Volatilization in Open dirt Feedlots In Proceedings of the Eighth Interna tional Symposium on Animals, Agriculture and Food Processing Wastes; ASAE Press: St Joseph, MO, 2000; 204 297 14 Satter, L.D.; Klopfenstein, T.J.; Erickson, G.E The role of nutrition in reducing nutrient output from ruminants J Anim Sci 2002, 80 (E Suppl 2), E143 E156 15 Klopfenstein, T.J.; Erickson, G.E Effects of manipulating protein and phosphorus nutrition of feedlot cattle on nutrient management and the environment J Anim Sci 2002, 80 (E Suppl 2), E106 E114 16 Wang, S.J.; Fox, D.G.; Cherney, D.J.; Chase, L.E.; Tedeschi, L.O Whole herd optimization with the Cornell net carbohydrate and protein system III Application of an optimization model to evaluate alternatives to reduce nitrogen and phosphorus mass balance J Dairy Sci 2000, 83, 2160 2169 Nutrient Management: Water Quality/Use J L Hatfield United States Department of Agriculture, Agricultural Research Service, Ames, Iowa, U.S.A INTRODUCTION Animals generate a valuable source of nutrients in both organic and inorganic forms Nutrients in manure can be a valuable soil amendment; however, if manure is misused, it can be a potential water quality problem Water quality is a primary concern among environmental issues; manure application is the focus of this article MANURE NUTRIENTS Nutrients vary among species, manure handling, and storage systems as shown in Table Nutrient content is affected by species, diet, age, sex, manure storage system, and length of time in storage Values shown in Table illustrate the nutrient content in different manure storage systems but not represent the full range of variation within a species or among manure storage systems These data provide an indication of the variation among species and the need for nutrient management systems to consider animal production systems and manure storage systems before making assumptions about the best management system The goal in nutrient management is to develop a system in which manure nutrients may be applied to the soil to supply the crop needs without being a potential environmental problem WATER QUALITY CONCERNS In nutrient management, water quality concerns focus on phosphorus (P) and nitrate-nitrogen (NO3-N) Broadcast manure on the soil surface provides for potential surface runoff conditions, particularly when rain occurs shortly after application In a 2001 study, broadcasting manure resulted in the greatest potential for surface runoff of soluble P.[2] Kleinman and Sharpley[3] compared dissolved reactive phosphorus from three manures at six rates under simulated rainfall and found that dissolved reactive phosphorus loss was related to runoff and manure application rate Soluble P losses were a function of the type of manure, the application rate, and soil type Broadcast manure on the soil surface increases the potential for surface runoff into nearby surface water Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019732 Published 2005 by Marcel Dekker, Inc All rights reserved bodies In addition, surface runoff of manure may provide pathogens that are present in manure a pathway into nearby water bodies There are few studies of this problem and the evidence is insufficient to provide a set of factors that contribute to pathogen movement Incorporation of manure into the soil greatly reduces the chances of surface runoff Tabbara[4] showed that incorporation of manure or fertilizer 24 hours before a heavy rainfall reduced both dissolved reactive P or total P concentrations by as much as 30% to 60% depending on the nutrient source and application rate The incorporation process moves P below the volume of soil eroded under high rainfall events To reduce potential surface losses of P, manure should be incorporated on soils with intensive erosive rain, recent extensive tillage, or little or no surface residue Incorporation of manure will reduce the likelihood of surface runoff of P and protect surface water from excess P levels; however, the process of incorporating manure may increase the potential for sediment loss from the soil The development of management practices that protect soil from surface runoff will decrease potential losses of manure P into nearby water bodies Incorporation of manure may lead to NO3-N leaching because nutrients placed below the surface mixing layer are in a soil volume where leaching of nutrients can occur NO3-N present in the manure may be moved into deeper soil layers by soil water However, there is no evidence that this is a direct result of manure application Incorporation of manure changes the availability of nutrients in the soil profile Nutrients present in manure are in the organic form and the conversion into available forms is a function of biological activity and time in the soil profile Klausner et al.[5] developed a method to estimate the decay rate for organic nutrients from dairy manure that has worked well for this species over a range of environmental conditions One of the challenges for manure management is to determine the temporal patterns of nutrient availability from different manure types and species Jokela[6] showed that NO3-N levels were actually lower in soils treated with dairy manure compared to commercial fertilizer because of the slower release of NO3-N from manure Nutrient patterns in manured soils can lead to potential water quality problems; however, these can be managed through a proper rate of application and incorporation 667 668 Nutrient Management: Water Quality/Use Table Nutrient content in solid and liquid manure for different species and manure handling systems Solid manure storage Total N Species 50 21 18 76 K2O (g/kg) Dry matter % Beef Dairy Poultry Swine P2O5 Liquid manure storage 10.5 4.5 19.0 6.5 9.0 1.5 22.5 4.0 Total N Dry matter % 13.0 3.0 12.5 2.5 10 P2O5 K2O (g/l) 3.5 3.7 7.2 4.3 2.2 1.8 5.4 3.0 3.1 2.3 3.6 2.6 (From Ref 1.) Water quality problems can be reduced through relatively simple management practices that increase nutrient availability to the crop and decrease the potential for offsite movement through runoff or leaching EFFECT OF MANURE ON SOIL PROPERTIES RELATED TO WATER QUALITY Addition of manure to soil causes changes in the soil properties[7,8] that reduces the likelihood of water quality problems Water infiltration rate, soil water-holding capacity, cation exchange capacity, bulk density, organic matter, biological activity, and plant availability of nutrients are changed by manure additions These changes required at least five years of manure additions to the soil A positive impact on water quality is derived from increased water infiltration rates and water storage capacity Surface runoff occurs in soils that quickly develop Fig a surface seal and ponding begins on the soil surface leading to the development of small rills that transport water along the surface Manure-amended soils have a larger infiltration rate and more rainfall can enter the soil before saturation occurs This change is not a direct effect of manure addition but a combination of increased biological activity and organic materials that create a more stable soil particle that has a higher soil water content before becoming saturated The higher waterholding capacity of soil allows more absorption before the profile is saturated Eghball et al.[9] concluded that the increased intensity of rainfall could cause surface runoff but changes in the soil properties from manure could offset water quality problems Addition of manure to soil not only changes the soil properties but also restores the soil to a higher level of soil productivity Freeze et al.[10] found that the application of manure to eroded soil was of greater benefit than application to noneroded soils Changes in soil Conceptual diagram of nutrient flows in the MINAS systems for the Netherlands (Adapted from Ref 11.) Nutrient Management: Water Quality/Use properties are more detectable in eroded soils These effects of manure can be realized with all sources and types of manure Often the water quality problems that occur in agriculture are from soils that are in a degraded state and restoration of soil properties will benefit the environment 669 manure on soil properties will benefit livestock, crop producers, and the environment REFERENCES NUTRIENT ACCOUNTING FROM MANURE SOURCES To achieve water quality goals and manure application requires the proper amount of nutrients added to the soil to supply crop requirements The components in a nutrient budget are rates of crop removal, change in the soil nutrient content, and amount supplied from manure In the Netherlands, nutrient accounting systems have been developed for livestock and cropping systems Ondersteijn et al.[11] described the mineral accounting system (MINAS) and provided a framework for nutrient accounting (Fig 1) Manure that is produced is accounted for through the MINAS approach to ensure that both an economic and environmental quality goal is achieved Development of nutrient management guidelines for producers to help guide their decisions can have a positive impact on environmental quality CONCLUSION Nutrient management programs must have a positive impact on water quality The challenge for producers is to understand the nutrient balance in the soil and to reduce the risk of surface runoff of manure The challenge for science is to increase our understanding of the value of manure in the soil and in the restoration of eroded soils to a higher level of productivity Improved methods for sampling manure to determine the nutrient content from individual farms and for manure application that incorporates manure to reduce erosion and enhance the value of 10 11 MWPS (MidWest Plan Service) Manure Storages Ma nure Management System Series MWPS 18, Section MidWest Plan Service Iowa State University: Ames, IA, 50011 3080, 2001 Zhao, S.L.; Gupta, S.C.; Huggins, D.R.; Moncrief, J.F Tillage and nutrient source effects on surface and subsurface water quality at corn planting J Environ Qual 2001, 30, 998 1008 Kleinman, P.J.A.; Sharpley, A.N Effect of broadcast manure on runoff phosphorus concentrations over succes sive rainfall events J Environ Qual 2003, 32, 1072 1081 Tabbara, H Phosphorus loss to runoff water twenty four hours after application of liquid swine manure or fertilizer J Environ Qual 2003, 32, 1044 1052 Klausner, S.D.; Kanneganti, V.R.; Bouldin, D.R An approach for estimating a decay series for organic nitrogen in animal manure Agron J 1994, 86, 897 903 Jokela, W.E Nitrogen fertilizer and dairy manure effects on corn yield and soil nitrate Soil Sci Soc Am J 1992, 56, 148 154 Sommerfeldt, T.G.; Chang, C Changes in soil properties under annual applications of feedlot manure and different tillage practices Soil Sci Soc Am J 1985, 49, 983 987 Sommerfeldt, T.G.; Chang, C Soil water properties as affected by twelve annual applications of cattle feedlot manure Soil Sci Soc Am J 1987, 51, Eghball, B.; Gilley, J.E.; Baltensperger, D.D.; Blumenthal, J.M Long term manure and fertilizer application effects on phosphorus and nitrogen in runoff Trans ASAE 2002, 45, 687 694 Freeze, B.S.; Webber, C.; Lindwall, C.W.; Dormaar, J.F Risk simulation of the economics of manure application to restore eroded wheat cropland Can J Soil Sci 1993, 87, 267 274 Ondersteijn, C.J.M.; Beldman, A.C.G.; Daatselaar, C.H.G.; Giesen, G.W.J.; Huirne, R.B.M The Dutch mineral accounting systems and the European nitrate directive: Implications for N and P management and farm perfor mance Agric Ecosyst Environ 2002, 92, 283 296 Nutrient Requirements: Carnivores Duane E Ullrey Michigan State University, East Lansing, Michigan, U.S.A INTRODUCTION Carnivores, broadly defined, sustain themselves by feeding on vertebrate or invertebrate animal tissues, a practice observed in both the animal and plant kingdoms The Venus flytrap (Dionaea muscipula), one of over 500 carnivorous plant species, lives in humid, acidic bogs in the Carolinas and, like most plants, acquires energy and nutrients by photosynthesis and through the roots In this environment, nitrogen and some mineral elements are in short supply, and these needs are met by capturing insects attracted to nectar in a specialized leafy trap, functioning both as a mouth and stomach Animals, of course, not possess roots or the mechanisms of photosynthesis Thus, energy and nutrient requirements of wild carnivorous animals are acquired principally by consuming vertebrate or invertebrate prey.[1,2] Wilson[3] estimated there are about 4000 species of extant mammals, 9000 of birds, 6300 of reptiles, 4200 of amphibians, and 18,000 of fish and lower chordates The nutrient requirements of these species are presumed to be qualitatively similar, but quantitative nutrient requirements have been defined by the National Academy of Sciences/National Research Council (NAS/NRC) only for humans and a few domesticated or captive mammals, birds, and fish Of the species with NRC-defined requirements, the cat, mink, tarsiers, rainbow trout, and salmon are obligate carnivores The NRC also has defined the nutrient requirements of the dog and fox, but these species appear to be facultative carnivores and may consume considerable vegetable matter CARNIVOROUS MAMMALS The immediate ancestors of the domestic cat (Felis catus) were strictly carnivorous, and its needs have been the most thoroughly studied of any of the obligate carnivores Although commercial diets for cats may contain vegetable matter, the nutrients and the amounts that must be present reflect a long evolutionary dependence on a strictly carnivorous diet The cat has a simple digestive system, presumably because digestibility of natural prey tends to be high, and there is no need for extended food retention and microbial fermentation Due to its limited ability to 670 conserve nitrogen, the cat has a high protein requirement, and it converts only negligible amounts of tryptophan to niacin (neither ability is necessary when consuming whole prey) Requirements for blood glucose are met primarily by gluconeogenesis rather than from dietary carbohydrate, and the cat has a high requirement for arginine for disposal of nitrogen via the urea cycle It requires taurine and arachidonic acid because of limited tissue synthesis (vertebrate prey provide adequate amounts), and it is unable to convert b-carotene (a plant provitamin) to vitamin A Vitamin D3 needs are met by diet because cutaneous concentrations of 7-dehydrocholesterol (provitamin D3) are insufficient to support vitamin D photobiogenesis Nutrient needs of the cat have been reviewed by the NRC,[4] and minimal requirements, adequate intakes, and recommended allowances have been published The NRC-recommended allowances for growth, maintenance, late gestation, and peak lactation are presented in Table The mink (Mustela vison) eats small mammals, fish, frogs, crayfish, insects, worms, and birds in the wild Like the cat, its protein requirements are high 38% of dietary dry matter (DM) from weaning to 13 weeks of age, 22 26% for adult maintenance, 38% for gestation, and 46% for lactation.[5] Whether the mink shares the other unique metabolic features of the cat has not been determined Tarsiers (Tarsius spp.) eat insects (beetles, ants, locusts, cicadas, cockroaches, mantids, moths) and sometimes small vertebrates in the wild Although the quantitative nutrient requirements of tarsiers have not been specifically defined, estimated adequate nutrient concentrations in dietary DM have been proposed.[6] When kept in captivity, tarsiers are often provided crickets as a major food item Because crickets and other commercially available insects tend to be deficient in certain nutrients (particularly calcium, vitamin A, and vitamin D),[7] specifically formulated diets are offered to these insects for about 48 hours before feeding them to tarsiers so that the insects plus their gut contents will be nutritionally complete.[8–10] Other obligate carnivorous mammals include felids such as lions, tigers, leopards, cheetahs, and jaguars Aquatic mammals such as dolphins, seals, sea lions, and walruses also are obligate carnivores, but little is known about their quantitative nutrient requirements Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019733 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Nutrient Requirements: Carnivores 671 Table Recommended nutrient allowances in dietary dry matter (DM) for domestic cats consuming diets containing kcal of metabolizable energy per g of DM Nutrient Growth Crude protein, % Arginine, % Histidine, % Isoleucine, % Methionine, % Meth + cystine, % Leucine, % Lysine, % Phenylalanine, % Phenyl + tyrosine, %a Threonine, % Tryptophan, % Valine, % Taurine, %b Total fat, % Linoleic acid, % a Linolenic acid, % Arachidonic acid, % Eicosapentaenoic and docosahexaenoic acid, % Calcium, % Phosphorus, % Magnesium, % Sodium, % Potassium, % Chloride, % Iron, mg/kg Copper, g/kg Zinc, mg/kg Manganese, mg/kg Selenium, mg/kg Iodine, mg/kg Vitamin A, IU/kg Vitamin D3, IU/kg RRR a tocopherol, mg/kg Vitamin K (menadione), mg/kg Thiamin, mg/kg Riboflavin, mg/kg Pyridoxine, mg/kg Niacin, mg/kg Pantothenic acid, mg/kg Folic acid, mg/kg Biotin, mg/kg Vitamin B12, mg/kg Choline, mg/kg 22.5 0.96 0.33 0.54 0.44 0.88 1.28 0.85 0.50 1.91 0.65 0.16 0.64 0.04 0.2 9.0 0.55 0.02 0.02 0.01 a 0.80 0.72 0.04 0.14 0.40 0.09 80 8.4 75 4.8 0.4 2.2 3,550 250 38 1.0 5.5 4.25 2.50 42.5 6.25 0.75 75 22.5 2,550 Maintenance 20.0 0.77 0.26 0.43 0.17 0.34 1.02 0.34 0.50 1.53 0.52 0.13 0.51 0.04 0.2 9.0 0.55 0.004 0.01 0.29 0.26 0.04 0.07 0.52 0.10 80 5.0 75 4.8 0.4 2.2 3,550 250 38 1.0 5.6 4.25 2.50 42.5 6.25 0.75 75 22.5 2,550 Late gestation Peak lactation 21.3 1.50 0.43 0.77 0.50 0.90 1.80 1.10 30.0 1.50 0.71 1.20 0.60 1.04 2.00 1.40 1.91 0.89 0.19 1.00 0.04 0.2 9.0 0.55 0.02 0.02 0.01 1.08 0.76 0.06 0.13 0.52 0.20 80 8.8 60 7.2 0.4 2.2 7,500 250 38 1.0 5.5 4.25 2.50 42.5 6.25 0.75 75 22.5 2,550 1.91 1.08 0.19 1.20 0.04 0.2 9.0 0.55 0.02 0.02 0.01 1.08 0.76 0.06 0.13 0.52 0.20 80 8.8 60 7.2 0.4 2.2 7,500 250 38 1.0 5.5 4.25 2.50 42.5 6.25 0.75 75 22.5 2,550 At least twice as much phenylalanine (or phenylalanine plus tyrosine) is required for maximal black hair color as for growth Recommended taurine allowances are lowest when diets are unprocessed (0.04% of DM) but are increased by extrusion (0.1% of DM) or canning (0.2% of DM) (Adapted from Ref 4, recommended allowances for growth of an 800 g kitten, maintenance or late gestation of a kg adult cat, and lactation of a kg queen with four kittens.) b 672 CARNIVOROUS BIRDS The digestive systems of obligate carnivorous birds (such as hawks and eagles), like their mammalian counterparts, not have compartments adapted for microbial fermentation Relatively indigestible portions of prey, such as fur, feathers, bones, fins, scales, shells, and exoskeletons, may be separated from more digestible portions by the beak prior to food ingestion Sometimes, this separation is accomplished in the gizzard, followed by egestion of indigestible matter out of the mouth, as in owls.[11] Although the NRC[12] has defined the nutrient requirements of poultry, these species are principally herbivorous Based on present metabolic evidence and the composition of vertebrate and invertebrate prey, it seems likely that nutrient needs of carnivorous birds are similar to those of carnivorous mammals, with adjustments for differences in reproductive strategy Nutrient Requirements: Carnivores indeed obligate carnivores, their nutrient needs seem to deviate from those of the cat Most amphibians appear to be obligate carnivores.[13] Adult frogs and toads consume invertebrates and small vertebrates, although most species are herbivorous as larvae (tadpoles) and have a long, coiled intestine permitting them to digest plant matter At metamorphosis, the intestine is much shortened and the diet becomes strictly carnivorous Tadpoles of a few species are carnivorous and have a much shorter gut than herbivorous tadpoles Salamanders and newts are carnivorous both as larvae and as adults, feeding on insects, slugs, snails, and worms Caecilians (limbless, viviparous amphibians) prey on worms, termites, and orthopterans Metabolic features characteristic of carnivory have not been well studied in amphibians CARNIVOROUS FISH CARNIVOROUS REPTILES AND AMPHIBIANS The long evolutionary association of snakes, crocodilians, and some lizard families with subsistence on vertebrate and invertebrate prey suggests that they are obligate carnivores They tend to have simple gastrointestinal systems as compared to herbivorous reptiles, although there are adaptations related to the periodicity of feeding and to unique characteristics of certain food items Tortoises are chiefly herbivorous with a few that are omnivorous Turtles tend to be omnivorous carnivorous as juveniles and herbivorous or omnivorous as adults although a few species are mostly carnivorous throughout life.[13] Studies that define qualitative or quantitative needs of reptiles are few, although protein and amino acid needs of the hatchling green sea turtle (Chelonia mydas; carnivorous as hatchlings, herbivorous as adults) have been investigated Some studies suggest that young redeared slider turtles (Trachemys scripta elegans) and green anoles (Anolis carolinensis) not have an elevated requirement for arginine (as does the cat), and addition of taurine to a diet based on plant proteins does not improve growth of young American alligators (Alligator mississippiensis) Also, American alligators appear to convert linoleic acid to arachidonic acid to some extent, although rates may not be optimum for maximum growth.[1] When a purified diet containing adequate tryptophan but no niacin was administered weekly by stomach tube to bull snakes (Pituophis melanoleucus sayi) for 132 days, no signs of deficiency were seen, suggesting that either a longer period of depletion is necessary to induce niacin deficiency or metabolic conversion of tryptophan to niacin may occur in this species.[14] Thus, if these reptiles are Rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kirsutch) have protein requirements of ! 40% of dietary DM for maximal growth of juveniles and have an absolute requirement for arginine They also lack the ability to synthesize niacin from tryptophan Gluconeogenesis is important for provision of blood glucose, and essential fatty acid requirements include linoleic acid and eicosapentaenoic acid and/or docosahexaenoic acid.[15] CONCLUSIONS Qualitative and quantitative nutrient requirements of obligate carnivores generally appear to reflect evolutionary adaptations to the composition of ancestral diets REFERENCES Allen, M.E.; Oftedal, O.T The Nutrition of Carnivorous Reptiles In Captive Management and Conservation of Amphibians and Reptiles, Contributions to Herpetology, Vol 11; Murphy, J.B., Adler, K., Collins, J.T., Eds.; Society for the Study of Amphibians and Reptiles: Ithaca, NY, 1994; 71 82 Allen, M.E.; Oftedal, O.T.; Baer, D.J The Feeding and Nutrition of Carnivores In Wild Mammals in Captivity: Principles and Techniques; Kleiman, D.G., Allen, M.E., Thompson, K.V., Lumpkin, S., Eds.; Univ Chicago Press: Chicago, IL, 1996; 139 147 Wilson, E The Diversity of Life; Harvard Univ Press: Cambridge, MA, 1992 National Research Council Nutrient Requirements of Dogs Nutrient Requirements: Carnivores and Cats; National Academies Press: Washington, DC, 2004 National Research Council Nutrient Requirements of Mink and Foxes, 2nd Rev.; National Academy Press: Wash ington, DC, 1982 National Research Council Nutrient Requirements of Nonhuman Primates, 2nd Rev Ed.; National Academies Press: Washington, DC, 2003 Finke, M.D Complete nutrient composition of commer cially raised invertebrates used as food for insectivores Zoo Biol 2002, 21, 269 285 Allen, M.E.; Oftedal, O.T Dietary manipulation of the calcium content of feed crickets J Zoo Wildl Med 1989, 20, 26 33 Finke, M.D Gut loading to enhance the nutrient content of insects as food for reptiles: A mathematical approach Zoo Biol 2003, 22, 147 162 673 10 11 12 13 14 15 Roberts, M.; Kohn, F Habitat use, foraging behavior, and activity patterns in reproducing Western tarsiers, Tarsius bancanus, in captivity: A management synthesis Zoo Biol 1993, 12, 217 232 Klasing, K.C Comparative Avian Nutrition; CAB Inter national: New York, NY, 1998 National Research Council Nutrient Requirements of Poultry; National Academy Press: Washington, DC, 1994 The Encyclopedia of Reptiles and Amphibians; Halliday, T.R., Adler, K., Eds.; Facts on File, Inc.: New York, NY, 1986 Bartkiewicz, S.E.; Ullrey, D.E.; Trapp, A.L.; Ku, P.K A preliminary study of niacin needs of the bull snake (Pituophis melanoleucus sayi) J Zoo Anim Med 1982, 13, 55 58 National Research Council Nutrient Requirements of Fish; National Academy Press: Washington, DC, 1993 Nutrient Requirements: Nonruminant Herbivores Michael R Murphy Amy C Norman University of Illinois at Urbana Champaign, Urbana, Illinois, U.S.A INTRODUCTION Nonruminant herbivorous mammals include a small number of commercially important animals and a larger number of wild species.[1] Digestive strategies clearly differ among these herbivores Mammals lack enzymes to hydrolyze a substantial portion of plant material (cell walls), but various pregastric (including ruminant) and postgastric microbial fermentation systems have evolved that enable herbivorous mammals to utilize fibrous substrates Digestive strategy and body size data for East African nonforest herbivores indicated that ruminants dominated medium body sizes, whereas nonruminants prevailed among very large and small herbivores[2] (Fig 1) Our objective was to briefly review current knowledge about the nutritional requirements of nonruminant herbivores Those for horses (Equus caballus) and domestic rabbits (Oryctolagus cuniculus) are stressed Among commercially important and widely distributed species, horses and rabbits represent very large and small mammalian herbivores, respectively In addition, they exemplify subgroups of postgastric fermenters that emphasize colonic (horses) or cecal (rabbits) function More detailed information is also available on their nutritional requirements than for many other species HORSES Water Horses usually drink to L of water/kg of dry matter consumed Water intake increases with lactation, exercise, and elevated temperatures by 50 to 70%, 20 to 300%, and up to 300%, respectively Ad libitum access to fresh, clean water is recommended except after intense exercise, when horses should be allowed to drink only small amounts every to 10 minutes for approximately hour.[3] energy).[4] Structural carbohydrates, such as cellulose and hemicellulose, often make up the majority of their diet[3] and are fermented by microbes in the cecum and colon to provide much of the energy required by a horse at maintenance.[4] A minimum of 12 to 15% fiber is presumed necessary to minimize incidence of colic and laminitis, but forages alone not generally provide sufficient energy for growing, working, or lactating horses, so cereal grains are added to their diets Cereal grains provide digestible nonstructural carbohydrate (starch).[4] Lipids may also be supplemented, providing 2.25 times the energy value of carbohydrates,[5] and 20% added fat can be included in the diet without adverse effects.[4] Diets supplemented with fat should be monitored closely for rancidity, because spoiled feed is not accepted Supplementation with fat improves work output, reproductive performance, milk production, and foal growth, but it must be monitored closely to avoid obesity and insulin resistance.[4] Protein Amino acids, the building blocks of protein, are required.[4] Protein deficiency retards growth of young horses and causes tissue loss, poor coat, and abnormal hoof development in the adult Average protein intake at maintenance is approximately 0.6 g of digestible protein/ kg/day and should be increased during late gestation and early lactation Protein requirements for working horses have not been clearly defined, but it is not considered advantageous to feed protein above the maintenance requirement High-quality protein is essential for the growing horse, and it appears that growth is maximal when the protein-to-energy ratio is 50 and 45 g of crude protein/Mcal of DE/day for weanlings and yearlings, respectively Lysine is the first-limiting amino acid for growing horses, and there appears to be no beneficial effect of including nonprotein nitrogen sources in practical diets for horses.[4] Energy Minerals and Vitamins Horses get most of their dietary energy from carbohydrates and lipids Energy value is usually expressed in terms of digestible energy (DE, gross energy minus fecal 674 The major minerals needed by horses are Ca, P, Na, K, Cl, I, Fe, Cu, Zn, Mg, and Se.[4] Bone is approximately 35% Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019734 Copyright D 2005 by Marcel Dekker, Inc All rights reserved Nutrient Requirements: Nonruminant Herbivores 675 toxicity Iron is adequate in most diets, so supplementation is unnecessary, although frequently practiced Vitamins are often classified as fat-soluble or watersoluble The former category includes vitamins A, D, E, and K Vitamin A is important for good vision Vitamin D is essential for calcium and phosphorus absorption, but rarely needs to be supplemented if animals are exposed to sunlight Water-soluble thiamin and riboflavin are discussed in a publication of the National Research Council (NRC).[4] A deficiency of thiamin can cause a multitude of problems, but neither deficiency nor toxicity of riboflavin has been reported Requirements for other watersoluble vitamins (niacin, pantothenic acid, pyridoxine, biotin, folacin, B12, ascorbic acid, and choline) have not been determined, but they are presumed to be required Table summarizes nutrient requirement data for horses Fig The relationship between digestive strategy and body size in 186 species of East African nonforest herbivores (Adapted from Ref 2, with the sizes of rabbits and horses marked for comparison.) (View this art in color at www dekker.com.) Ca and 16% P The dietary Ca:P ratio is critical for proper bone development; ratios less than 1:1 can impair Ca absorption and cause detrimental bone abnormalities in developing horses Sodium, K, and Cl are the three major minerals involved in electrolyte balance, and it is necessary to maintain proper concentrations of each Iodine is important for regulation of metabolism, but it should be closely monitored because horses are susceptible to iodine RABBITS Mature rabbits vary greatly in size, from to kg.[6] Therefore, their nutrient requirements are not usually specified on an amount-per-day basis, but on a dietary concentration relative to body size, or relative to metabolic body size basis Table Estimated nutrient requirements for a 500 kg mature horse Unita Growth Maintenance L Mcal of digestible energy g 23 30 14 19 720 850 38 45 16.5 656 g g g g % % mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg 34 29 19 16 11.3 17.8 3.7 5.5 0.15 0.1 50 40 40 10 0.1 0.1 0.6 0.1 IU/kg IU/kg IU/kg 2,000 800 80 Nutrient Water Energy Protein Minerals Calcium Phosphorus Potassium Magnesium Sulfur Sodium Iron Manganese Zinc Copper Selenium Iodine Cobalt Vitamins A D E a Amounts or concentrations on a dry matter basis (From Refs and 4.) Gestation Lactation Work 38 57 18 19 801 866 38 57 28 24 1,427 1,048 38 68 20 33 820 1,300 20 18 25 7.5 0.15 0.1 40 40 40 10 0.1 0.1 0.6 0.1 35 37 26 28 29.1 31.5 8.7 9.4 0.15 0.1 50 40 40 10 0.1 0.1 0.6 0.1 56 36 36 22 46 33 10.9 8.6 0.15 0.1 50 40 40 10 0.1 0.1 0.6 0.1 25 40 18 29 31.2 49.9 9.4 15.1 0.15 0.3 40 40 40 10 0.1 0.1 0.6 0.1 2,000 300 50 3,000 600 80 3,000 600 80 2,000 300 80 676 Water Although the NRC[6] did not address the subject of water, others[7,8] have noted that the water requirements of rabbits fed dry feed far exceed their dry matter intakes Consumption of such diets drops precipitously if water is withheld Water intake on dry diets is about 120 mL/kg of rabbit, or twice the amount of feed consumed Environmental temperature also influences water consumption, increasing it by 67% between 18 and 308C High-quality drinking water should always be available Energy For diets containing 12 to 15% digestible protein, DE and metabolizable energy (ME, DE minus urinary energy in nonruminants) are closely correlated, and ME is about 95% of DE Diet ME and net energy (ME minus heat increment) contents are more difficult to determine than DE, so DE values are still commonly used in practical rabbit feeding.[8] Rabbits not utilize plant fiber as efficiently as widely assumed[6] and coprophagy (consumption of soft feces of cecal origin) does not appear to greatly influence the overall efficiency of fiber digestion.[7] Cellulose and hemicellulose digestibilities in rabbits are similar to those of rats, and less than in horses and guinea pigs Only about 10% of neutral detergent fiber in timothy hay was digested by rabbits, compared to about 35% for horses and ponies Rabbit growth rate is apparently optimal with diets having 13 to 25% acid detergent fiber A minimum of 10% dietary crude fiber is needed to maximize growth rate (and to prevent enteritis and fur pulling), but over 17% depresses growth by restricting feed intake Starches, sugars, and lipids apparently pose no special problems for rabbits The likelihood of a deficiency of essential fatty acids is remote, but it has been demonstrated in rabbits Protein Rabbits need adequate quantities of essential amino acids in their diet for rapid growth, and nonprotein nitrogen cannot be employed usefully in grower diets.[6] Protein quality must allow essential amino acid requirements to be met Required and optimal concentrations of some amino acids have been established for growing and lactating rabbits.[6–8] Rabbits are able to utilize 64 to 90% of the crude protein in common feedstuffs.[7] They can maintain positive nitrogen balance when fed gelatin, a protein devoid of the essential amino acid tryptophan, because of the consumption of microbial protein via coprophagy Negative nitrogen balance occurred when coprophagy Nutrient Requirements: Nonruminant Herbivores was prevented Increased feed intakes can compensate for low protein concentrations in diets Therefore, it is desirable to express protein requirements per unit of energy Growth is optimized with about 55 mg of crude protein/kcal of DE Minerals and Vitamins The rabbit is unusual because serum Ca concentration reflects dietary Ca concentration, rather than being homeostatically regulated in a narrow range as in other species.[6,7] Hypocalcemia is sometimes observed in late gestation or early lactation It is treatable with Cagluconate injection However, whether an acidotic diet during late gestation would be prophylactic, as it is for a dairy cow, is not known.[8] Requirements for many minerals have not been well studied, although deficiencies and problems with excesses have often been demonstrated Vitamin A deficiency and toxicity have been demonstrated, but precise requirements have not been determined.[7,8] Any dietary requirement for vitamin D is likely Table Estimated nutrient requirements for rabbits (amounts are per kilogram of air dry diet, unless otherwise specified) Nutrient Water Energy Protein Minerals Calcium Phosphorus Potassium Sodium Chlorine Magnesium Iron Zinc Copper Manganese Iodine Cobalt Selenium Vitamins A D E K Unit Growth Lactation kg kcal MJ kJ of digestible energy/kg0.75 g 1.6 2,500 10.5 950 2.0 2,500 10.5 1,200 170 180 170 180 g g g g g g mg mg mg mg mg mg mg 3 50 25 10 8.5 0.2 0.1 0.01 11.8 6.6 2.2 3.2 75 50 10 10 0.2 0.1 0.01 IU IU mg mg 6,000 1,000 35 10,000 1,000 45 (Mean or median values compiled from Refs 8.) Nutrient Requirements: Nonruminant Herbivores much lower than for other species The only practical problem encountered with vitamin D in rabbit nutrition is toxicity: 2300 to 3000 IU of vitamin D/kg are detrimental Vitamin E deficiency has been demonstrated, but recommendations are based primarily on old data or extrapolation from other species Vitamin K is probably not of practical concern in rabbit nutrition because it is synthesized in the cecum, and no requirement studies have been conducted Under practical conditions, B-complex vitamins are not dietarily essential for rabbits, but deficiencies have been demonstrated Addition of B vitamins to commercial rabbit feeds has not shown benefits Rabbits can synthesize vitamin C, so it is not a dietary essential either In commercial diets, it is advisable to include a vitamin mixture that provides at least moderate concentrations of vitamins A and E to ensure that no deficiency occurs Table summarizes nutrient requirement data for rabbits CONCLUSION Much remains unknown about the nutritional requirements of nonruminant herbivores Current data, however, allow many practical dietary limitations and toxicities to be avoided in commercially important and 677 widely distributed species, particularly horses and domestic rabbits REFERENCES Cork, S.J.; Hume, I.D.; Faichney, G.C Digestive Strategies of Nonruminant Herbivores: The Role of the Hindgut In Nutritional Ecology of Herbivores; Jung, H J.G., Fahey, G.C., Jr., Eds.; Amer Soc Anim Sci.; Savoy: IL, 1999; 210 260 Demment, M.W.; Van Soest, P.J A nutritional explanation for body size patterns of ruminant and nonruminant herbivores Am Nat 1985, 125, 641 672 Lawrence, L Feeding Horses In Livestock Feeds and Feeding, 5th Ed.; Kellems, R.O., Church, D.C., Eds.; Prentice Hall: Upper Saddle River, NJ, 2002; 381 401 National Research Council Nutrient Requirements of Horses, 5th Rev Ed.; Natl Acad Sci.: Washington, DC, 1989 Ensminger, M.E.; Oldfield, J.E.; Heinemann, W.W Feeds and Nutrition, 2nd Ed.; Ensminger Publ Co.: Clovis, CA, 1990 National Research Council Nutrient Requirements of Rab bits, 2nd Rev Ed.; Natl Acad Sci.: Washington, DC, 1977 Cheeke, P.R Rabbit Feeding and Nutrition; Academic Press: Orlando, FL, 1987 de Blas, C.; Wiseman, J The Nutrition of the Rabbit; CABI Publ.: New York, 1998 Nutrient Requirements: Ruminants C L Ferrell United States Department of Agriculture, Agricultural Research Service, Clay Center, Nebraska, U.S.A INTRODUCTION Nutrient needs of tissues of ruminants are similar to those of nonruminants Tissues of ruminants require oxygen, water, energy, amino acids, fatty acids, minerals, and fatand water-soluble vitamins Dietary needs of ruminants are simpler and often cheaper than for nonruminants because of anaerobic microbial metabolism in the rumen Microbial metabolism of dietary intake also increases the complexity of relating dietary intake to nutrients available to the animal WATER Water is required by the animal for regulation of body temperature and acts as a solvent necessary for transport of nutrients, metabolites, and waste products The requirement for water reflects needs for accretion in body tissues (e.g., growth, pregnancy) and milk production plus that lost from the animal Water is lost from the animal by excretion as urine or feces, from the lungs as water vapor during respiration, and from skin by evaporation Losses vary considerably and depend in part on activity, air temperature, diet, and water consumption Because feeds contain water, and oxidation of nutrients produces water, not all water needs must be provided by drinking ENERGY Energy is defined as the potential to perform work and is required to perform the ‘‘work’’ of living Energy requirements depend on the additive needs of individual cells and vary according to physiological needs imposed upon those cells Energy is derived from the metabolism of carbohydrates, proteins or amino acids, and fats and can be supplied from the diet, or if dietary supply is inadequate, from body tissues (fat, protein, glycogen) Carbohydrates are the primary dietary source of energy of ruminants Dietary protein, peptides, and amino acids contribute up to about 20% to the energy supply Fat is low (2 4%) in diets typically consumed by ruminants, and is, thus, not a major contributor to energy supplies Fat 678 may be added to diets of feedlot cattle or lactating cows to increase the energy density of the diet, but dietary fat contents of greater than 10% may have adverse effects on rumen microbial metabolism Cellulose, hemicellulose, and starch are the major carbohydrates utilized by ruminants Many species of bacteria in the rumen produce cellulase enzymes capable of hydrolyzing the b linkages between the glucose units in cellulose and others hydrolyze the b linkages in hemicellulose Many species of microbes, as well as a amylases present in pancreatic secretions of all animals, hydrolyze a linkages of starch The symbiotic relationship between ruminants and rumen microbes allow utilization of forages and other feeds, especially those containing complex carbohydrates such as cellulose that are unusable or poorly utilized by nonruminants Volatile fatty acids (VFA; acetate, proprionate, butyrate, etc.) are primary metabolic end-products of carbohydrate (and protein) hydrolysis by anaerobic microbes in the rumen and serve as the major energy source of ruminants One of the major metabolic differences between ruminants and nonruminants is the reliance of ruminants on VFAs as the major substrates for oxidative metabolism and energy storage Little glucose is available for absorption from the digestive tract of ruminants However, glucose is required by nervous tissue, muscle, adipose, mammary gland, and gravid uterus Glucose requirements of ruminants are met through gluconeogenesis, primarily from proprionate, amino acids (e.g., alanine, glutamine, aspartate, glutamate), glycerol, and lactate In spite of the lower blood glucose concentrations and extra metabolic steps required to provide glucose, requirements of ruminants appear to be similar to nonruminants AMINO ACIDS It is generally assumed that tissue requirements for amino acids of ruminants are similar to those of nonruminants However, this assumption has not been rigorously tested Amino acids are required for synthesis of protein and other essential compounds and provide the carbon skeleton for a major proportion of glucose needed by the ruminant Lysine, arginine, histidine, isoleucine, Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019736 Published 2005 by Marcel Dekker, Inc All rights reserved Nutrient Requirements: Ruminants leucine, methionine, phenylalanine, threonine, tryptophan, and valine must be supplied from the digestive tract, but specific requirements have not been well defined Requirements have been estimated based on rate of accretion and amino acid composition of whole body protein.[1] Ruminants have the unique ability to subsist and produce without dietary protein or amino acids due to synthesis of microbial protein from a wide variety of nitrogen (N) sources within the rumen The sources of N that microbes utilize for protein synthesis include dietary protein and nonprotein N (NPN), as well as N recycled to the rumen via saliva or diffusion (primarily as urea) Most ruminal bacteria can use ammonia N as a source of N, but much of the N used by bacteria is derived from amino acids or peptides, if available Ruminants can grow, reproduce, and lactate with only NPN as a source of N, but additional sources of amino acids are required to achieve maximal productivity Rumen microbes, as well as dietary protein that escape (bypass) degradation in the rumen, supply the intestine with protein for digestion and absorption as amino acids Microbial N composes about 40% of the nonammonia N entering the intestine on highenergy diets with high protein levels, about 60% with low protein diets, and 100% with purified, NPN-supplemented diets Biological values of microbial protein range from about 65 to 90, with an ideal value of 100 The quantity and quality of protein reaching the small intestine is modulated by the effects of degradation and synthesis in the rumen Both quality and quantity of protein available to the animal may be improved by microbial metabolism if a diet containing a low level or low quality of protein is fed Microbial action may decrease the quantity and quality of available protein when a diet containing a high level of high-quality protein is fed The amino acid profile of microbial protein is relatively constant and well balanced relative to tissue needs, and thus is utilized very efficiently However, dietary protein escaping ruminal degradation may be less well balanced As with nonruminants, a poorly balanced supply of amino acids results in increased catabolism of amino acids Unless used for synthesis of protein or other essential compounds, amino acids are catabolized with the N being converted to urea and the carbon skeleton being oxidized or used for storage A poorly balanced amino acid supply results in inefficient use of N and is energetically costly MINERALS At least 17 minerals are required by ruminants Macrominerals (those required in large amounts) include calcium, magnesium, phosphorus, potassium, sodium, chlo- 679 rine, and sulfur Required microminerals (those required in small amounts) are chromium, cobalt, copper, iodine, iron, manganese, molybdenum, nickel, selenium, and zinc.[1–3] Other minerals including arsenic, boron, lead, silicon, and vanadium have been shown to be essential for one or more animal species, but there is no evidence to indicate these minerals are of practical importance in ruminant diets Two features of ruminant nutrient requirements are noteworthy Phytate phosphorus is not well utilized by nonruminants, but as a result of microbial fermentation, is utilized readily by ruminants Cobalt functions as a component of vitamin B12 Ruminants are not dependent on a dietary source of vitamin B12, but cobalt is required for its synthesis by rumen microbes Many of the essential minerals are usually found in typical feeds, while others must be provided by dietary supplementation for optimal animal performance Supplementation in excess of requirements increases mineral excretion In addition, several essential minerals (e.g., copper and selenium) are toxic at high levels, while others, although not toxic per se, interfere with absorption of other essential minerals when included in the diet in excessive amounts VITAMINS Ruminants require fat-soluble vitamins (A, D, E, and K) and water-soluble vitamins (B complex), but typically only have a dietary requirement for vitamins A and E Vitamin A is essential for normal growth and reproduction, maintenance of epithelial tissues, and bone development, and is a constituent of the visual pigment rhodopsin present in the rod cells of the retina Vitamin A (retinol) per se does not occur in plants, but its precursors, carotenes, occur in various forms Betacarotene is the most widely distributed High-quality forages provide carotenes in large amounts, but tend to be seasonal Carotenes are rapidly destroyed by sunlight and air Conversion of carotenes to retinol occurs in intestinal mucosal cells, but efficiency of conversion tends to be lower in ruminants than in nonruminants Functions of vitamin E include serving as an antioxidant and in the formation of cellular membranes Vitamin E occurs in feedstuffs as a-tocopherol Vitamin E requirements depend on dietary concentrations of antioxidants, sulfur-containing amino acids, and selenium Because vitamin D is synthesized by ruminants exposed to sunlight, or fed sun-cured forages, these animals rarely require vitamin D supplementation Physiological needs of Vitamin K and the B vitamins (e.g., B12, thiamin, niacin, riboflavin, pyridoxine, pantothenic acid, biotin, and choline) have been clearly demonstrated, but 680 requirements are normally easily met by microbial synthesis in the rumen CONCLUSIONS At the tissue level, nutrient requirements of ruminants are believed to be similar to those of nonruminants However, a symbiotic relationship between the animal and microbes within the digestive tract (especially in the rumen and reticulum) results in several unique features of ruminant dietary requirements In particular, complex carbohydrates, such as cellulose, can be effectively digested and metabolized by rumen microbes Volatile fatty acids (VFA), by-products of microbial fermentation of carbohydrates or protein, provide a major proportion of the energy available to ruminants Dietary protein, amino acids, or nonprotein nitrogen, such as urea, may be incorporated into microbial protein, which serves as the primary source of amino acids to ruminants Alternatively, amino acids from the diet may escape microbial Nutrient Requirements: Ruminants fermentation in the rumen and become available for intestinal absorption In addition, urea produced within the animal may be recycled to the digestive tract, thus providing a source of N for microbial synthesis of amino acids Similarly, B vitamins, vitamin K, and essential fatty acids are normally produced in sufficient quantities by microbial fermentation to meet animal requirements; however, microbial synthesis of vitamin B12 requires a dietary source of cobalt REFERENCES NRC Nutrient Requirements of Beef Cattle, 6th Revised Ed.; National Academy Press: Washington, DC, 2000; Update NRC Nutrient Requirements of Sheep, 6th Revised Ed.; National Academy Press: Washington, DC, 1985 NRC Nutrient Requirements of Dairy Cattle, 6th Revised Ed.; National Academy Press: Washington, DC, 1989 Update  ... sunlight and air Conversion of carotenes to retinol occurs in intestinal mucosal cells, but efficiency of conversion tends to be lower in ruminants than in nonruminants Functions of vitamin E include... Washington, DC, 2004 National Research Council Nutrient Requirements of Mink and Foxes, 2nd Rev.; National Academy Press: Wash ington, DC, 1982 National Research Council Nutrient Requirements of Nonhuman...Nutrient Management: Diet Modification 665 NITROGEN UTILIZATION NITROGEN FOR RUMINANTS Nitrogen (N) is a part of amino acids (AA) that form proteins required by all animals; animals consume