Effects of dietary ratios of fish and blood meals on sites of digestion, small intestinal amino acid disappearance and growth performance of meat goat wethers

Six yearling Boer × Spanish wether goats (37 ± 1.6 kg initial live weight; LW) and 24 growing Boer × Spanish and 24 Spanish wethers (21 ± 3.1 and 20 ± 2.6 kg initial LW, respectively) were used to determine the effects of total CP and two supplemental protein sources (fish meal, FIM; blood meal, BLM) in a 70% concentrate diet on sites of digestion, small intestinal amino acid disappearance and growth performance. Diets were formulated to be 12 or 15% CP (DM basis), with predicted ruminally undegraded intake protein (UIP) from FIM and BLM of 1.2 and 3.0% DM, respectively, achieved from FIM supplying 100, 67 and 33% and BLM 0, 33 and 67%, respectively (100F, 67F and 33F, respectively). True ruminal OM and N digestibilities were greater (P < 0.05) for 12% versus 15% CP and decreased linearly (P < 0.05) as level of FIM decreased. Duodenal flows of both microbial and non-microbial, non-ammonia (feed plus endogenous) N were greater (P < 0.05) for 15% than for 12% CP and increased linearly with decreasing FIM level in the diet. Correspondingly, small intestinal disappearance of essential amino acids was greater (P < 0.05) for 15% versus 12% CP and increased (P < 0.05) with decreasing FIM. In an 18-week growth experiment, DM intake (935 g/day versus 783 g/day), average daily gain (ADG; 145 g versus 108 g) and ADG:DM intake (155 g/kg versus 138 g/kg) were greater (P < 0.05) for Boer × Spanish compared with Spanish wethers. Regardless of genotype, neither level of total CP nor of FIM influenced growth performance. In conclusion, with diets relatively high in concentrate and a CP level of 12%, amino acid requirements of common genotypes of growing meat goats in the US may be satisfied by basal dietary ingredients, with little or no potential to enhance performance by addition of feedstuffs high in UIP regardless of amino acid profile.