SUPPLEMENTAL PROTEIN INFLUENCES ON CARBOHYDRATE DEGRADATION AND BACTERIAL 16S RIBOSOMAL RIBONUCLEIC-ACID

This research examined the mechanism by which soybean protein stimulates growth of mixed ruminal anaerobes and degrades structural polysaccharides in vitro. Soybean meal, isolated soy protein, or branched-chain VFA was added to orchardgrass hay;substrate in Experiment 1. Cell-wall degradation increased 14.5% over that of the control by protein addition. Protein addition resulted in 1.3- to l.5-fold increases in bacterial growth. Hybridization with a 16S probe specific for Fibrobacter succinogenes indicated that protein addition did not influence the proportion of this species. For in vitro Experiment 2, optimal protein for cell-wall degradation was 2 g/L in cultures containing tall fescue hay. To determine whether protein stimulated microbial colonization of plant cell wall (Experiment 3), orchardgrass hay was placed in 14-L fermentors; treatments were control, NH3 N (2 g of N/L), or isolated soy protein (2 g of N/L). Addition of protein and NH3 N increased the extent of cell-wall disappearance 9.7% above control. Protein and ammonia improved cell-wall digestion, but protein had the greatest stimulatory effect on prokaryote growth with no preferential effect of F. succinogenes.