Influence of niacin on in vitro ruminal fermentation and microbial synthesis depending on dietary factors

Abstract

The in vitro degradability of starch by ruminants as influenced by supply of niacin was studied with different dietary factors, and compared to that of fibre (beet pulp) within similar dietary conditions. The batch cultures were supplied rumen contents from cows fed four diets based either on maize silage or on hay, supplemented with soybean meal and urea. Starch, beet pulp or niacin were introduced directly into fermenters. Regardless of niacin supplementation, maize silage and starch intensified fermentations and microbial synthesis when compared respectively to hay and beet pulp. Oil supply did not modify starch fermentation. Niacin enhanced production of total and individual gas and volatile fatty acids, as well as fermented organic matter and ammonia nitrogen uptake, irrespective of dietary conditions. However, responses to niacin were higher with maize silage than with hay, but similar whatever the nitrogen source, oil supply and energy substrate. Treatments did not affect efficiency of microbial synthesis, except for the depression due to added oil. Collectively, these results indicate that sufficient quantities of substrate for maximum growth of microbes would make subsequent positive fermentative and microbial synthesis responses to niacin more probable.