Addition of Branched- and Straight-Chain Volatile Fatty Acids to Purified Lamb Diets and Effects on Utilization of Certain Dietary Components1

Abstract

Metabolic studies were conducted to determine the effect that short-chain volatile fatty acids have on utilization of various dietary components. It was determined that isobutyric and isovaleric acids were present in minimal quantities in rumen fluid of lambs fed a purified diet devoid of intact protein. A conventional balance trial was conducted with eight lambs consuming a purified diet containing 39% cellulose, and urea as the sole nitrogen source. Four of the lambs received a mixture of isobutyric, isovaleric and n-val-eric acids. The addition of the acid mixture significantly increased the apparent nitrogen digestibility (P<.01) and nitrogen retention (P<.05). The cellulose and dry-matter digestibility coefficients were also improved by the acid addition. Further experimentation showed that addition of the acid mixture to the diet decreased the ammonia level in the rumen at various intervals after feeding, but had no effect on TCA precipitable nitrogen. A balance trial with lambs consuming a diet containing 59% cellulose was also conducted. Addition of the acids to the diet did not show any apparent advantage in terms of digestibility of diet components or nitrogen balance. The acid addition tended to increase diet acceptability. It was also determined that the amino acid composition of bacterial protein hydrolysates from acid-treated and control lambs did not differ significantly.