INFLUENCE OF NIACIN ON IN-VITRO RUMINAL FERMENTATION AND MICROBIAL SYNTHESIS DEPENDING ON DIETARY FACTORS

The in vitro degradability of starch by ruminants as influenced by sup ply of niacin was studied with different dietary factors, and compared to that of fibre (beet pulp) within similar dietary conditions. The b atch cultures were supplied rumen contents from cows fed four diets ba sed either on maize silage or on hay, supplemented with soybean meal a nd urea. Starch, beet pulp or niacin were introduced directly into fer menters. Regardless of niacin supplementation, maize silage and starch intensified fermentations and microbial synthesis when compared respe ctively to hay and beet pulp. Oil supply did not modify starch ferment ation. Niacin enhanced production of total and individual gas and vola tile fatty acids, as well as fermented organic matter and ammonia nitr ogen uptake, irrespective of dietary conditions. However, responses to niacin were higher with maize silage than with hay, but similar whate ver the nitrogen source, oil supply and energy substrate. Treatments d id not affect efficiency of microbial synthesis, except for the depres sion due to added oil. Collectively, these results indicate that suffi cient quantities of substrate for maximum growth of microbes would mak e subsequent positive fermentative and microbial synthesis responses t o niacin more probable.