Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion of fresh, dry and ensiled sweet potato (ipomoea batatas l (lam )) leaves

Animal Feed Science and Technology 114 (2004) 127–139 Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion of fresh, dry and ensiled sweet potato (Ipomoea batatas L (Lam.)) leaves Le Van An a , Tran Thi Thu Hong a , Jan Erik Lindberg b,∗ b a Hue University of Agriculture and Forestry, 24 Phung Hung St., Hue City, Vietnam, Sweden Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, P.O Box 7024, S-750 07 Uppsala, Sweden Received 20 May 2003; received in revised form November 2003; accepted 15 December 2003 Abstract Ileal and total tract digestibility in growing pigs fed cassava root meal (CRM) based diets with inclusion of fresh, dry and ensiled sweet potato leaves was studied in a × Latin square design Four diets were formulated with CRM and casein (CAS), fresh sweet potato leaves (FSP), dry sweet potato leaves (DSP) and ensiled sweet potato leaves (ESP) The control diet (CAS) contained 100 g casein per kg DM The experimental diets FSP, DSP, and ESP contained 350, 350 and 400 g DM of fresh, dry and ensiled sweet potato leaves per kg DM diet, respectively Leaves were separated manually from stems and only the leaf part was used The daily feed intakes of dry matter (DM) and dietary components were significantly different between diets (P < 0.05) There was no difference in ileal apparent digestibility of OM between diets (P > 0.05), while the total tract apparent digestibility of OM and crude protein (CP) was higher on diet CAS than on diets FSP, DSP and ESP (P < 0.05) The ileal apparent digestibility of CP and essential amino acids (EAA), except for arginine, threonine and tyrosine, were higher for diet CAS than for diets FSP, DSP and ESP (P < 0.05) The ileal digestibility of NDF and the total tract digestibility of crude fibre (CF) were lower for diet CAS than for diets FSP, DSP and ESP (P < 0.05) Abbreviations: AA, amino acids; ADF, acid detergent fibre; CAS, casein diet; CF, crude fibre; CP, crude protein; CRM, cassava root meal; DM, dry matter; DSP, dry sweet potato leaf diet; EAA, essential amino acids; EE, ether extract; ESP, ensiled sweet potato leaf diet; FSP, fresh sweet potato leaf diet; NDF, neutral detergent fibre; NEAA, non-essential amino acids; OM, organic matter ∗ Corresponding author Tel.: +46-18-672102; fax: +46-18-67-2995 E-mail address: jan-eric.lindberg@huv.slu.se (J.E Lindberg) 0377-8401/$ – see front matter © 2004 Elsevier B.V All rights reserved doi:10.1016/j.anifeedsci.2003.12.007 128 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 There were no differences (P > 0.05) in digestibility of OM, CP, CF, NDF, ADF and most EAA among sweet potato leaf diets However, there was a tendency (P = 0.064) of a lower ileal apparent digestibility of lysine in the dried and ensiled sweet potato leaves It was concluded that, sweet potato leaves have the potential to improve dietary protein and amino acid supply in low fibre diets for pigs Further, the optimum strategy for preserving sweet potato leaves can be decided on from consideration of the prevailing climatic conditions, as the general nutritional properties were similar for fresh, sun-dried and ensiled sweet potato leaves © 2004 Elsevier B.V All rights reserved Keywords: Amino acids; Fibre; Digestibility; Sweet potato leaves; Pigs Introduction In Vietnam, pig production is increasing annually at a rate of about 4.5%, with a total of 22 million pigs produced in 2001 (Statistical Yearbook, 2002) In addition to providing protein for human consumption, pig production is important as it is the main source of cash income of resource-poor farmers in rural areas and provides manure for cropping Farmers in the rural areas of Vietnam, account for over 75% of the total pig production in the country However, there is a shortage of suitable homegrown feed resources, in particular feedtuffs with an acceptable protein content and quality, for the growing pig population Commercial feeds are partly based on imported feedtuffs and are too expensive to be used by resource-poor farmers Thus, commercial feeds are mainly used in the large-scale of industrial pig production located around the major cities in the country Sweet potato (Ipomoea batatas L (Lam)) is the third most common crop in Vietnam after rice and maize, and has high biomass yields of both tubers and vines (An et al., 2003) Traditionally, sweet potato was used as human food when rice was not sufficient, although at present it is commonly used as feed for farm livestock, especially pigs The tubers have a high carbohydrate content while the leaves are rich in protein, and both tubers and vines can be used as animal feed (Woolfe, 1992) The vines include the leaf and stem, with a crude protein content in the leaves of 260–330 g kg−1 DM compared with 100–140 g kg−1 DM in the stems (Woolfe, 1992; Ishida et al., 2000; An et al., 2003) It has been shown that the leaves makes up approximately half of the sweet potato vines biomass (Woolfe, 1992; An et al., 2003) Thus, if the leaves could be separated from the stems a considerable improvement with respect to the dietary protein and amino acid supply would be expected (An et al., 2003) Earlier studies have indicated that vegetative plant parts may have nutritional properties that should allow them to be used in diets for pigs This applies to temperate forages (Lindberg and Andersson, 1998; Reverter et al., 1999) as well as to tropical green biomass (Phuc et al., 2001) Phuc and Lindberg (2000) showed that cassava leaves, leucaena leaves and groundnut foliage could be used to improve the dietary protein and amino acid supply to growing pigs under tropical conditions However, as indicated from studies on lucerne, the nutritional properties of lucerne leaf meal (Lindberg and Cortova, 1995; Reverter and Lindberg, 1998) is superior to that of the whole plant (Lindberg and Andersson, 1998; Reverter et al., 1999) Dominguez and Ly (1997) also concluded that the proportion of L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 129 sweet potato vines in diets for pigs should be kept low to avoid negative effects on nutrient digestibility, and they called for new methods to improve the digestibility of this potentially valuable feed resource This study was conducted to determine the ileal and total tract digestibility in growing pigs of nutrients, in particular crude protein and amino acids, in sweet potato leaves which had been separated from the stems Also, the influence of preservation method on the digestibility was evaluated by feeding the sweet potato leaves in fresh, dried and ensiled form Materials and methods 2.1 Animals Four 13-weeks old crossbred (Large White × Mong Cai) castrated male pigs from the same litter, with an average body weight of 25.4 ± 0.6 kg were used The pigs were vaccinated against pasteurellosis and hog cholera, surgically fitted with a post-valve T-caecum cannula (Van Leeuwen et al., 1991) and kept for weeks to recover from surgery before the experimental diets were introduced Pigs were kept individually in metabolism cages and had free access to water from nipple drinkers The experiment was conducted in the period March and April 2002 during which time outdoor temperatures ranged from 22 to 28 ◦ C 2.2 Diets and feeding Sweet potato leaves were harvested at 60 days after planting, with subsequent harvests at 20-day intervals The vines were separated into leaf and stem and only the leaf part was used in this experiment Fresh sweet potato leaves were harvested daily from the field and were chopped into 1–2 cm long pieces prior to feeding Dried sweet potato leaves were made by chopping the leaves into 2–3 cm long pieces, which were spread out on concrete out-doors in the sun for 2–3 days The dried leaves were collected and milled through a mm screen, stored in a dry place, and mixed with CRM at the time of feeding For ensiling, sweet potato leaves were chopped into small pieces 2–3 cm long and spread out on the floor overnight for wilting to reduce the moisture content Cassava root meal was used as additive at 60 g kg−1 of the wilted weight of the leaves and also common salt (NaCl) was added at g kg−1 of the wilted weight of the leaves The silage was kept in sealed air-tight plastic bags with a capacity of 30 kg and was stored for 21 days prior to feeding The ensiled sweet potato leaves were removed from the plastic bags twice daily and were mixed with CRM at the time of feeding In the casein diet (CAS) protein was supplied by casein and in the other three diets fresh sweet potato leaves (FSP), dried sweet potato leaves (DSP) and ensiled sweet potato leaves (ESP) were included as the sole protein sources (Table 1) The four diets were based on CRM and contain formulated to 120 g crude protein kg−1 DM (Table 2) Soybean oil was added at a level of 40 g kg−1 to the FSP, DSP and ESP diets (Table 2) to equalize the calculated content of metabolisable energy of the diets Chromium oxide was used as a digesta flow marker and was added at g kg−1 DM weight of the diets A vitamin and micromineral mixture was added at g kg−1 (Table 2) 130 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 Table Dry matter (DM, g kg−1 material), organic matter (OM), crude protein (CP), ether extract (EE), crude fibre (CF), NDF, ADF (g kg−1 DM) and metabolisable energy (ME, MJ kg−1 DM) contents of ingredients Ingredients DM OM CP EE CF NDF ADF ME Cassava root meal Fresh SPL Dried SPL Ensiled SPL 893 180 950 328 983 986 986 985 29 268 269 234 19 7 12 32 128 128 125 93 285 254 247 36 182 171 137 13.2 9.5 9.5 9.7 SPL: sweet potato leaves Daily feed allowance was kg 100 kg−1 of body weight for each individual animal, and was adjusted at the start of each experimental period The pigs were fed two times per day at 06.00 and 18.00 h, with the daily allowance equally divided between the two meals Food refusals and spillage were recorded, and were used to correct the food intake data Table Ingredients, analysed chemical composition (g kg−1 DM), calculated metabolisable energy content (ME, MJ kg−1 DM) and daily intake (g per day) of the diets Dieta CAS FSP DSP ESP Ingredients Cassava root meal Casein Fresh sweet potato leaves Dried sweet potato leaves Ensiled sweet potato leaves Chromic oxide Premixb 890 100 – – – 5 640 – 350 – – 5 640 – – 350 – 5 590 – – – 400 5 Chemical composition Organic matter (OM) Crude protein (CP) Crude firbre (CF) NDF ADF Metabolisable energy (ME)c 976 120 28 84 32 13.2 975 120 65 157 87 13.2 975 120 65 146 83 13.2 975 120 68 154 76 13.2 1187 a 141 a 1068 b 127 b 1249 a 147 a 1047 b 123 b Mean daily intake Dry matter (DM) Crude protein (CP) S.E.M P 36.2 4.24 0.005 0.006 a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet b Premix composition per kg: 2400 mg retinol; 4.32 mg cholecalciferol; 15,000 mg ␣-tocopherol; 5000 mg phytylmenaquirone; 2000 mg thiamin; 15,000 mg riboflavin; 25,000 mg calcium pantothenate; 30,000 mg niacin; 30 mg cyanocobalamin; 2000 mg folic acid; 100 mg choline; 100 mg Fe; 115 mg Zn; 40 mg Cu; 0.15 mg Co; 0.6 mg I; 0.3 mg Se c The calculated ME values were reached by addition of soyabean oil, which was mixed with the other diet ingredients at the time of feeding To FSP, DSP and ESP were added 40 g of soyabean oil per kg DM of diet L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 131 2.3 Experimental design The experiment was designed as a × Latin square and lasted for a total of 48 days Each of the four experimental periods was 12 days and comprised days of adaptation to each diet, days of collection of faeces, followed by day of collection of ileal digesta, day rest and a second day of collection of ileal digesta 2.4 Digesta, faeces collection and calculations For the determination of ileal digestibility, a total of 12 digesta samples from each pig was taken during the days of collection in each experimental period On each day of collection, samples were taken after every h during the 12 h period between the morning and afternoon feedings, giving six samples per day of collection At each sample collection, digesta were quantitatively collected for h in a container through a soft plastic tubing connected to the ileal cannula The digesta were frequently removed from the tube and container and transferred to a bigger container where they were kept on ice during sampling The samples were then kept frozen at −18 ◦ C For total tract digestibility, faeces were collected four times per day and kept in a freezer at −18 ◦ C Finally, prior to chemical analysis, individual samples of ileal digesta and faeces were thawed and pooled within pigs and periods The digestibility of the diets at each sampling site was calculated using the indicator technique (Sauer et al., 2000) according to the equation: CADD = − (DCF × ID ) (DCD × IF ) where is CADD the coefficient of apparent digestibility of dietary component in the assay diet; DCF the dietary component concentration in ileal digesta or faeces (g kg−1 ); ID the indicator concentration in the assay diet (g kg−1 ); DCD : dietary component concentration in the assay diet (g kg−1 ); If the indicator concentration in ileal digesta or faeces (g kg−1 ) The coefficient of apparent ileal digestibility of CP and amino acids in sweet potato leaves (CIADSPL ) was estimated by difference from the values of the assay diets (CIADD ) and those of the cassava root meal (CIADCRM ) CIADSPL = CIADD − (CIADCRM × PCRM ) PSPL where is CIADSPL the coefficient of apparent ileal digestibility of CP and amino acids in sweet potato leaf in the assay diet; CIADD the coefficient of apparent ileal digestibility of CP and amino acids in the assay diet; CIADCRM the coefficient of apparent ileal digestibility of CP and amino acids of cassava root meal; PCRM the proportion of CP and amino acids coming from cassava root meal in the assay diet; PSPL : proportion of CP and amino acids coming from sweet potato leaves in the assay diet The coefficient of apparent ileal digestibility of CP and amino acids in cassava root meal (CIADCRM ) was estimated by difference from values of the control diet (CIADCAS ) by using the coefficient of ileal standardized digestibility (CISDC ) for CP and amino acids in 132 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 casein (Pedersen and Boisen, 2002) according to the equations: CIADCRM = CISDC − CIADCAS PCRM where is CIADCRM the coefficient of apparent ileal digestibility of CP and amino acids of cassava root meal, CISDC the coefficient of ileal standardized digestibility of CP or amino acids in casein; CIADCAS the coefficient of apparent ileal digestibility of CP and amino acids in the control diet; PCRM the proportion of CP and amino acids coming from cassava root meal in the assay diet 2.5 Chemical analysis Food, digesta and faecal samples were dried at 60 ◦ C for 24 h and milled through a mm screen before analysis All analyses were performed on dried samples, except for nitrogen (N) in ileal digesta and faeces, which was determined on fresh samples Dry matter (DM; method 930.15), ash (method 942.05), crude protein (CP, N × 6.25; method 988.05) and crude fibre (CF; method 978.10) were determined in dry samples according to standard AOAC methods (AOAC, 1990) Neutral detergent fibre (NDF) was analysed according to Robertson and Van Soest (1977), with addition of sodium sulfite and alpha amylase Acid detergent fibre (ADF) was analysed according to Goering and Van Soest (1970) NDF and ADF values were expressed without residual ash Chromium was determined by atomic absorption spectrometry after ashing according to Fenton and Fenton (1979) Amino acids were analysed according to Spackman et al (1958) on an ion-exchange column using a HPLC 2.6 Statistical analysis Analysis of variance was performed according to a × Latin square arrangement, using the General Linear Model of Minitab Statistical Software Version 12.2 (1998) Tukey pair-wise comparisons were used to determine differences between treatment means at P < 0.05 Results 3.1 Intake The chemical composition of the ingredients is presented in Table and of the experimental diets in Table The CP content of fresh and dried sweet potato leaves was similar, while a lower value was found in ensiled sweet potato leaves Also, the content of amino acids differed between fresh, dried and ensiled sweet potato leaves (Table 3) Thus, the proportion of total EAA in ensiled sweet potato leaves was 0.95 of that in fresh leaves Further, the contents of arginine (0.95), histidine (0.82), lysine (0.87), methionine (0.82), cystine (0.69), tyrosine (0.91) and glycine (0.66) were lower in the ensiled than in the fresh material Also, in the sun-dried sweet potato leaves the contents of histidine (0.89), lysine (0.92), cystine (0.95), tyrosine (0.96) and glycine (0.86) were lower than in the fresh material There was no difference in CF content between fresh, dried and ensiled sweet potato L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 133 Table Amino acid composition of the fresh, dried and ensiled sweet potato leaves (g/16 g N) Essential amino acids (EAA) Arginine Histidine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Threonine Tyrosine Valine Non-essential amino acids (NEAA) Alanine Aspartic acid Glutamic acid Glycine Proline Serine Total amino acids Fresh Dried Ensiled 5.22 2.24 3.73 8.58 4.48 1.49 3.36 7.09 5.22 4.10 5.60 5.20 1.99 4.18 8.83 4.14 1.56 3.20 6.88 5.23 3.95 5.74 4.98 1.85 3.57 9.03 3.92 1.23 2.33 7.14 5.15 3.74 5.42 5.22 10.45 11.57 4.10 3.73 4.10 5.39 11.02 9.87 3.52 3.40 4.06 5.02 11.23 10.00 2.73 3.39 4.71 90.30 88.20 85.70 leaves The highest contents of NDF and ADF were found in fresh and lowest in ensiled sweet potato leaves All experimental diets had the same levels of CP and ME However the CF, NDF and ADF content was lowest in diet CAS There was no difference of CF, NDF and ADF between FSP, DSP and ESP diets Due to differences in DM intake (Table 2) and chemical composition of the diets, the daily intakes of CP (Table 2) and of OM, CF, NDF, ADF and AA were different (data not shown) between diets (P < 0.05) Diets CAS and DSP showed similar intakes of DM, CP and OM, as did diets FSP and ESP (P > 0.05) The lowest daily intakes of CF, ADF and NDF were recorded for diet CAS (P < 0.05) The NDF and ADF intakes were not different between diets FSP and ESP (P > 0.05), and were lower than those on diet DSP (P < 0.01) 3.2 Ileal and total tract apparent digestibility of nutrients There were no differences (P > 0.05) in the coefficients of ileal apparent digestibility (CIAD) of OM among diets (Table 4) However, the CIAD of CP was higher (P < 0.05) and the CIAD of NDF was lower (P < 0.05) on diet CAS than on diets FSP, DSP and ESP There were no differences between sweet potato diets (P > 0.05) in the CIAD of OM, CP and NDF The coefficient of total tract apparent digestibility (CTTAD) of OM and CP were higher (P < 0.05) and the CTTAD of CF was lower (P < 0.05) on diet CAS than on diets FSP, 134 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 Table Ileal and total tract apparent digestibility coefficients of nutrients in the experimental diets Dieta S.E P CAS FSP DSP ESP Ileal Organic matter Crude protein NDF 0.84 0.84 a 0.19 a 0.83 0.72 b 0.21 b 0.84 0.73 b 0.22 b 0.82 0.73 b 0.23 b 0.01 0.01 0.01 0.576 0.001 0.001 Total tract Organic matter Crude protein Crude fibre NDF ADF 0.94 a 0.86 a 0.51 a 0.54 0.40 0.88 b 0.75 b 0.57 b 0.58 0.41 0.85 b 0.74 b 0.57 b 0.55 0.34 0.88 b 0.75 b 0.59 b 0.56 0.36 0.01 0.01 0.01 0.02 0.02 0.001 0.001 0.001 0.525 0.139 a, b, c Values within row with different letters were significantly different (P < 0.05) a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet DSP and ESP There were no differences between diets in CTTAD of NDF and ADF, and no differences between sweet potato diets (P > 0.05) in CTTAD of OM, CP, CF, NDF and ADF The CIAD of most amino acids was lower in the diets which contained protein from sweet potato leaves than from casein (P < 0.05), except for threonine, alanine and glycine (Table 5) There were no differences in the CIAD of most of the amino acids between the sweet potato leaf diets (P > 0.05) The estimated CIAD and CTTAD of CP, CF, NDF, ADF and EAA in sweet potato leaves are presented in Table There were no differences in CIAD or CTTAD between fresh, dried and ensiled sweet potato leaves (P > 0.05) However, the CIAD for lysine tended (P = 0.064) to be higher in fresh than in dried and ensiled sweet potato leaves Discussion The CP and CF contents of the fresh sweet potato leaves used in the present study were in good agreement with earlier reports in the literature (Woolfe, 1992; Ishida et al., 2000; An et al., 2003) The content of CP in fresh sweet potato leaves was comparable to values reported for cassava and leucaena leaves (Phuc and Lindberg, 2001), while that of CF and NDF was lower than in cassava leaves, leucaena leaves and groundnut foliage (Phuc and Lindberg, 2000) Also, the content of amino acids in fresh sweet potato leaves was similar to values reported by An et al (2003), in a study including several varieties grown in Vietnam In general, the content of EAA in fresh sweet potato leaves was similar to levels found in other tropical foliages (Phuc et al., 2001) However, the content of lysine was lower in fresh sweet potato leaves than in cassava and leucaena leaves (Phuc and Lindberg, 2001) The content of EAA in ensiled sweet potato leaves was lower than in the dried material, in agreement with studies on cassava leaves (Phuc and Lindberg, 2001) The sun-drying of 135 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 Table Apparent ileal digestibility coefficients of amino acids in the experimental diets Dietsa S.E P CAS FSP DSP ESP 0.81 a 0.84 a 0.83 a 0.87 a 0.94 a 0.82 a 0.80 a 0.86 a 0.76 0.79 0.86 a 0.74 b 0.74 b 0.74 b 0.74 b 0.81 b 0.72 b 0.73 b 0.76 b 0.74 0.74 0.70 b 0.77 ab 0.76 b 0.73 b 0.76 b 0.77 b 0.73 b 0.74 b 0.75 b 0.73 0.73 0.72 b 0.73 b 0.79 ab 0.78 b 0.80 b 0.76 b 0.75 b 0.74 b 0.79 b 0.72 0.80 0.78 b 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.02 0.02 0.01 0.011 0.001 0.001 0.003 0.002 0.003 0.001 0.001 0.358 0.067 0.001 Non-essential amino acids Alanine 0.73 Aspartic acid 0.80 a Glutamic acid 0.90 a Glycine 0.74 Proline 0.90 a Serine 0.82 0.71 0.74 b 0.74 b 0.74 0.73 b 0.73 0.71 0.80 ab 0.75 b 0.72 0.72 b 0.75 0.75 0.80 a 0.77 b 0.73 0.78 b 0.75 0.02 0.01 0.03 0.01 0.01 0.02 0.345 0.032 0.022 0.851 0.001 0.069 Essential amino acids Arginine Histidine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Threonine Tyrosine Valine a, b, c Values within row with different letters were significantly different (P < 0.05) a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet sweet potato leaves did not affect the total content of EAA, although ensiling resulted in a reduction of the CP, NDF and ADF contents compared with the fresh material Also, the content of amino acids was affected by the ensiling process (reduced content of arginine, histidine, lysine, methionine, cystine, tyrosine and glycine) and also by sun-drying (reduced content of histidine, lysine, cystine, tyrosine and glycine) This is in agreement with a study where the contents of arginine, histidine, lysine and methionine were found to be lower in ensiled than in sun-dried cassava leaves (Phuc and Lindberg, 2001) The reduction in CP content in sweet potato silage could be due to microbial decomposition to ammonia during the ensiling process (An and Lindberg, 2004) Also, the change in AA content in ensiled sweet potato leaves can be explained by microbial activities during the ensiling process (McDonald et al., 1991) However, the reduced content of AA in sun-dried sweet potato leaves can be due to the action of endogenous plant enzymes during the initial phase of the drying process The lower content of NDF in sweet potato silage could be a result of losses in the chemical analysis caused by solubilisation of fibre constituents in the acid conditions prevailing in the ensiled product Man and Wiktorsson (2002) also reported a decrease in NDF content of and 4% after ensiling cassava top and gliricidia leaves, respectively Morrison (1979) reported that approximately 10–20% of the hemicellulose was solubilized during 150 day ensiling of forages The daily intakes of DM were lower (−13%) on the diets with FSP and ESP than on diets CAS and DSP Thus, the ensiling of sweet potato leaves did not have a negative influence 136 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 Table Estimated ileal and total tract digestibility coefficients of nutrients in sweet potato leaves Sweet potato leaves S.E P Fresh Dried Ensiled Ileal digestibility Crude protein NDF 0.74 0.23 0.74 0.24 0.74 0.25 0.01 0.01 0.790 0.233 Total tract digestibility Crude protein Crude fibre NDF ADF 0.76 0.61 0.57 0.36 0.75 0.61 0.55 0.32 0.77 0.62 0.56 0.36 0.01 0.02 0.02 0.02 0.386 0.758 0.544 0.201 Ileal AA digestibility Arginine Histidine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Threonine Tyrosine Valine 0.76 0.75 0.74 0.83 0.72 0.73 0.76 0.75 0.74 0.71 0.80 0.77 0.74 0.77 0.79 0.74 0.74 0.75 0.73 0.74 0.73 0.75 0.80 0.78 0.80 0.76 0.75 0.74 0.78 0.70 0.80 0.78 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.03 0.02 0.03 0.02 0.118 0.206 0.278 0.177 0.064 0.495 0.703 0.715 0.442 0.253 0.133 on the palatability compared with the fresh material The reduction in DM intake suggests that the way of presenting the foliage to the pigs may be of importance in maintaining a high daily feed intake Apparently, the reduction in water content by sun-drying and the subsequent reduction in particle size by milling helped to maintain feed intake at similar levels as in the control diet in the present study In contrast, in an earlier study on sun-dried and ensiled cassava leaves (Phuc and Lindberg, 2000), where the daily DM feed allowance was similar (4 kg 100 kg−1 ), feed intake was unaffected by the preservation method In the latter study, the diet was given as a wet mash in the proportion 1:1 (w/w), while in the present study no water was added to the diet in connection with feeding The CIAD and CTTAD of OM in the cassava root meal based control diet was similar to previously published values for similar diets (Phuc and Lindberg, 2000) However, the CIAD of CP, and the CTTAD of CP and OM were higher in the present study This can be explained by the lower digestibility values of soya bean meal, which was used as a protein source in the study by Phuc and Lindberg (2000), than that of casein (Martins et al., 2001) used in the present study The CIAD for CP in the control diet was in agreement with values reported by Peiniau et al (1996) feeding diets based on cassava starch, supplemented with casein, to weaned pigs When sweet potato leaves were included in the diet, the CIAD and CTTAD of CP and the CTTAD of OM were reduced This can be explained by the increase in fibre content of the diets and was in agreement with studies on inclusion of tropical foliages (Phuc and Lindberg, 2000), as well as inclusion of temperate forages (Lindberg and Andersson, 1998) L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 137 and other fibre-rich feedstuffs (Wenk, 2001) in diets for growing pigs A likely explanation for the reduced digestibility of protein and amino acids in fibre-rich diets is that amino acids are bound to or incapsulated in the cell wall and that fibre will stimulate secretion of endogenous nitrogen Also, a high content of insoluble fibre in the digesta increases the peristaltic action of the gut and, therefore, reduces the transit time, which may lead to an impaired digestibility Jørgensen et al (1996) reported that a high fibre diet (268 versus 59 g dietary fibre kg−1 DM) resulted in a five to six fold increase in the flow of digesta through the terminal ileum of growing pigs In the present study, the CIAD of OM was unaffected by an increase in dietary fibre content (84 versus 145–157 g NDF kg−1 DM), while there was a reduction of the CIAD (−0.12 units) and CTTAD (−0.11 units) of CP There were no differences in CIAD and CTTAD of dietary components between sweet potato leaf diets, suggesting that the preservation methods used resulted in products that were nutritionally similar, and not different from the fresh material This was in agreement with Phuc and Lindberg (2000), reporting similar nutritive values of sun-dried and ensiled cassava leaves in growing pigs Compared with other tropical forage sources studied in growing pigs, such as cassava leaves, groundnut foliage and leucaena leaves (Phuc and Lindberg, 2000), and leucaena meal (Ly et al., 1998), sweet potato leaves showed a higher CIAD of CP than those mentioned above Also, there were no differences in CIAD of AA between fresh, dried and ensiled sweet potato leaves, with the possible exception of lysine The CIAD of lysine tended (P = 0.064) to be higher in fresh than in preserved sweet potato leaves, suggesting a reduced availability of lysine with drying and ensiling The reduction of ileal AA digestibility in sweet potato leaf diets could be due to an increase in the ileal flow of AA related to the properties of the feedstuff The changes in the ileal flow of AA could be the result of the increase of fibre in the diet (Boisen and Moughan, 1996; Jondreville et al., 2000) Similar results were found in growing pigs when including temperature forage meals in barley-based diets (Reverter and Lindberg, 1998; Reverter et al., 1999) The CIAD of EAA in sweet potato leaves was of a similar magnitude to that reported for groundnut foliage (Phuc and Lindberg, 2001) and lucerne leaf meal (Reverter and Lindberg, 1998) In contrast, the CIAD of EAA in sun-dried and ensiled cassava leaves, and in leucaena leaves, were markedly lower (Phuc and Lindberg, 2001) The higher CIAD for EAA in sweet potato leaves and groundnut foliage coincided with a high digestibility of dietary components (Phuc and Lindberg, 2000), including fibre, as did the lower CIAD of EAA in cassava and leucaena leaves Conclusion The present data suggests that sweet potato leaves have the potential to improve dietary protein and amino acid supply in low fibre diets for pigs The most suitable strategy for preserving sweet potato leaves can be decided from a consideration of the prevailing climatic conditions, as the general nutritional properties of fresh, sun-dried and ensiled sweet potato leaves are similar Possibly, the availability of lysine could be slightly lower in the dried and ensiled material, than in the fresh material Also, it should be noted that the content of EAA of sweet potato leaves can be affected by the preservation process which needs to be accounted for in diet formulation 138 L.V An et al / Animal Feed Science and Technology 114 (2004) 127–139 Acknowledgements Financial support from the Swedish International Development Cooperation Agency, Department for Research Co-operation (Sida-SAREC) program is gratefully acknowledged The authors would also like to thank Ms Dao Thi Phuong for her contribution to the experiment and Dr Le Van Tho for surgically fitting the PVTC cannula References An, L.V., Lindberg, B.E.F., Lindberg, J.E., 2003 Effect of harvesting interval and defoliation on yield and chemical composition of leaves, stems and tubers of sweet potato (Ipomoea batatas L (Lam.)) plant parts Field Crops Res 82, 49–58 An, L.V., Lindberg, J.E., 2004 Ensiling of sweet potato leaves (Ipomoea batatas (L.) 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Histidine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Threonine Tyrosine Valine Non-essential amino acids (NEAA) Alanine Aspartic acid Glutamic acid Glycine Proline Serine Total amino... availability of lysine with drying and ensiling The reduction of ileal AA digestibility in sweet potato leaf diets could be due to an increase in the ileal flow of AA related to the properties of the feedstuff... lysine was lower in fresh sweet potato leaves than in cassava and leucaena leaves (Phuc and Lindberg, 2001) The content of EAA in ensiled sweet potato leaves was lower than in the dried material,