VPB 121: Veterinary Physiology - II (2+1)

PROTEIN DIGESTION IN RUMINANTS

• Rumen microbial population have proteolytic activity. The diet of ruminants contains proteins and non-protein nitrogenous (NPN) substances (ammonia, nitrates, urea). Of the total proteins entering the rumen, 20 to 100% will be degraded to ammonia which are referred as rumen degradable protein (RDP).
• The fraction whch is not degraded by the microbes in the rumen escape and by-pass the microbial digestion, called as rumen undegradable protein (UDP); this fraction reaches the small intestine for enzymatic digestion by the animal.
• When the dietary proteins enter the rumen, the RDP fraction is hydrolysed by extracellular microbial proteases and produce short-chain peptides as end products.
• The peptides are absorbed into the microbial cell bodies. Within the microbial cells, the peptides can either be used for the formation of microbial protein or enter in to VFA pathways for energy production.

• The amino acids on deamination yield ammonia and a carbon skeleton; the carbon structures of many amino acids enter directly into various steps of the VFA pathways, leading to the formation of three major VFAs (Acetic, Butyric and Propionic acids).
• Three branched-chain amino acids valine, lucine and isoleucine are involved in the biosynthesis of branched-chain VFAs, the iso acids (isobutyrate, isovalarate and 2–methyl butyrate) which are growth promoters of cellulolytic rumen microbes.