Effects of zinc-treated soybean meal on ruminal fermentation and intestinal amino acid flows in steers fed corn silage-based diets.

The objectives of this study were to examine the effects of feeding zinc-treated soybean meal (Zn-SBM) on ruminal fermentation patterns and duodenal AA flows in steers fed diets based on corn silage and corn. Six steers (385 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a replicated 3 x 3 Latin square design experiment with 14-d periods. Diets were supplemented with solvent-extracted soybean meal (SBM), Zn-SBM, or a 50:50 combination (CP basis) of SBM:Zn-SBM. Ruminal escape N content of SBM and Zn-SBM were 30.0 and 57.0%, respectively, based on 12-h Dacron bag incubation. Protein sources provided approximately 30% of total CP in diets containing 12.6% CP (DM basis). Dry matter intake was equalized throughout the study at 2.2% of average initial BW. Total N flow at the duodenum was similar (P = .47) among treatments, but a trend (P = .15) for increased nonmicrobial N flow occurred when SBM and Zn-SBM were fed in combination. Micobial N flow and true efficiency of microbial CP synthesis were not affected by treatment (P = .87 and .37, respectively). Ruminal fermentation characteristics generally were unaffected (P > .10) by protein source. A positive quadratic response (P < .06) was observed for total and essential AA flows to the small intestine because flows of total and essential AA from ruminally undegraded dietary protein tended (P = .12) to increase when SBM and Zn-SBM were fed in combination. Absorption of AA from the small intestine also showed a positive quadratic (P < .06) response for SBM:Zn-SBM. Microbial AA flow to the small intestine was similar (P = .87) among treatments.(ABSTRACT TRUNCATED AT 250 WORDS)