Effect of nicotinic acid on rumen fermentation in vitro and in vivo.

A series of in vitro studies tested effects of nicotinic acid on rumen fermentation. Urea was the nitrogen supplement for all substances. As expected, a substrate of corn produced the most gas and microbial protein followed by a substrate of corn plus brome hay (1:1). A substrate of brome hay produced the least amount of gas and microbial protein. Niacin had no effect on gas production but significantly increased synthesis of microbial protein. The most protein was synthesized with the corn substrate, but the greatest percentage increase due to niacin was with the substance of corn plus hay. Six rumen-fistulated cows were fed a ration of grain and grass hay (1:1) with 2.3% urea. The rations were supplemented with 0 or 200 ppm niacin. Niacin had no important effect on the concentration of rumen dry matter or lactic acid, or the molar proportions of acetic, butyric, or valeric acids. Niacin increased the concentration of rumen bacterial protein, ammonia, and propionic acid. Niacin reduced the rumen concentration of urea nitrogen. There were no differences in the amino acid composition of rumen bacteria due to niacin.