Nitrogen digestion in forage-fed sheep with and without intraruminal propionate infusion

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Abstract
SUMMARY: Nitrogen balance and flow of nitrogen along the gastrointestinal tract were determined in growing wether sheep fed a dried grass pellet diet with or without intraruminal propionic acid infusion. Plasma free amino acid and glucose concentrations tended to be higher in peripheral blood of animals receiving propionate (P < 0·10). Overall total nitrogen and amino acid digestibilities and apparent digestibilities of each fraction along the digestive tract were not affected by infusion of propionic acid. The contribution of microbial amino acids to total amino acid flow in the duodenum measured using purine bases as the microbial marker averaged 0·49 and was not affected by propionic acid infusion. It is suggested that changes in circulating amino acid levels arise from reduced utilization of luminal amino acids by gastrointestinal tissues due to the increased availability of alternative energy-yielding substrates.