Supplemental Protein Influences on Carbohydrate Degradation and Bacterial 16S Ribosomal Ribonucleic Acid

¹ Department of Animal Sciences, University of Missouri, Columbia 65211

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 1.5-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.

Key Words: protein • cell-wall degradation • bacterial 16S ribosomal ribonucleic acid

Submitted on January 25, 1993
Accepted on May 20, 1993

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