Effects of level and source of supplemental protein in a concentrate-based diet on sites of digestion and small intestinal amino acid disappearance in Boer×Spanish wether goats

Twelve yearling Boer×Spanish wether goats fitted with ruminal, duodenal and ileal cannulae (34.5±1.39 kg average BW) were used in an experiment with two simultaneous 6×6 Latin squares to determine effects of different supplemental protein sources on sites of digestion and small intestinal amino acid disappearance with concentrate-based diets moderate or high in CP concentration. Diets were formulated to be 13 or 19% CP (DM basis), with supplemental protein provided by blood (BLM), corn gluten (CGM), cottonseed (CSM), feather (FTM), fish (FIM) or soybean meal (SBM). Small intestinal disappearance of the sum of essential amino acids measured (i.e., histidine, threonine, arginine, valine, methionine, isoleucine, leucine, lysine and phenylalanine) was greater for BLM versus SBM (39.0, 33.4, 28.7, 33.1, 33.3 and 20.5 g/day for BLM, CGM, CSM, FTM, FIM and SBM, respectively). Small intestinal disappearance of some essential amino acids was similar among CP sources with 13% CP but different with 19% CP. With 19% CP, small intestinal disappearance of histidine and valine was greatest (P < 0.05) among sources for BLM (histidine: 6.1, 1.8, 2.1, 1.9, 1.5 and 1.1 g/day; valine: 7.1, 3.6, 3.0, 4.3, 4.7 and 2.1 g/day), for leucine was greater (P < 0.05) for BLM and CGM than for CSM, FTM and SBM (13.2, 13.1, 5.8, 8.5, 9.3 and 4.4 g/day), of lysine was greater (P < 0.05) for BLM versus CGM, CSM, FIM and SBM (8.2, 3.2, 3.9, 5.5, 4.1 and 2.9 g/day) and of phenylalanine was lowest among sources for SBM (6.6, 5.2, 3.8, 3.9, 3.7 and 2.2 g/day for BLM, CGM, CSM, FTM, FIM and SBM, respectively). Essential amino acids with small intestinal disappearance not influenced by protein source within CP level were threonine, methionine and isoleucine. However, small intestinal disappearance of threonine (2.5 and 3.8 g/day) and methionine (1.1 and 1.9 g/day for 13 and 19% CP, respectively) was greater (P < 0.05) for 19% versus 13% CP diets. In conclusion, use of different feedstuffs high in protein not extensively degraded in the rumen and with unique amino acid concentrations in diets of goats may have little influence on small intestinal absorption of select amino acids with dietary CP levels, such as 13%, although effects may occur with much higher levels of CP (e.g., 19%). © 2005 Elsevier B.V. All rights reserved.