Balancing Diets to Meet the Animal’s Requirement for Absorbable Amino Acids

Source: J. W. Golden, M. S. Kerley, and N. A. Pyatt
A study was conducted to determine if growth rate and gain to feed ratio (GF) could be improved in feedlot steers by balancing the diet for absorbable amino acid requirements. The ruminally degradable protein (RDP) in the diet met, but did not exceed predicted degradable nitrogen required to maximize microbial efficiency. Two protein sources, bloodmeal (BM) and fishmeal (FM) were contrasted to test the hypothesis that diets could be formulated, based on absorbable amino acid requirements. BM and FM diets were whole corn based. The control diet (14%CP; SBM) was whole corn based with soybean meal and hay (10%). All diets contained a vitamin-mineral premix with Rumensin® and Tylan®. BM and FM diets were formulated to achieve an average daily gain (ADG) of 2.05 kg during phase one (P1; Day 0-84) and 1.70 kg for phase two (P2; Day 84-finish). Diets were optimized for RDP and microbial crude protein estimates were calculated using empirical equations. Amino acid requirements of feedlot steers were based upon the original CNCPS. ADG differed (P<0.10) during P1 between BM, FM, and SBM groups (1.79, 1.63, and 1.61 kg) with cattle fed BM having a greater ADG than FM and SBM. GF differed (P<0.10) during P1 between BM, FM, and SBM groups (0.26, 0.26, and 0.23) with BM and FM cattle having a greater GF ratio than SBM. Total pen manure was collected for one week during P1. Average pen wet manure weight (WMW) differed (P<0.10) between BM, FM, and SBM (117, 112, and 271 kg) with BM, and FM cattle excreting less manure than SBM. There were no differences in manure dry matter (DM) for BM, FM, and SBM groups during P1 (35.9, 39.6, and 38.7%). There was no difference in ADG (1.60, 1.45, and 1.54 kg) or GF (0.20, 0.20, and 0.17) for BM, FM, and SBM groups during P2. Total pen manure was collected for one week during P2. Average pen WMW differed (P<0.10) for BM, FM, and SBM (162, 151, and 268 kg) with BM, and FM cattle excreting less manure. There were no differences in manure DM between BM, FM, and SBM groups during P2 (42.7, 48.4, and 41.0%). We concluded from this research that animal performance can be improved when diets are formulated to meet the absorbable amino acid requirements.