EFFECT OF RAPESEED OIL-SUPPLY ON IN-VITRO RUMINAL DIGESTION IN COWS -COMPARISON OF HAY AND MAIZE SILAGE DIETS

The effect of lipid supply on carbohydrate fermentation and nitrogen m etabolism in the rumen was investigated using a closed fermenter conta ining rumen contents from cows receiving different diets. Four diets w ere compared. They were based either on hay or on maize silage, supple mented or not with 7% rapeseed oil, on a dry matter basis. Energy sour ce in the fermenters came either from starch or from sucrose. No suppl emental oil was added in the fermenters. Volatile fatty acid (VFA) pro duction was higher with maize silage diets than with hay diets. Oil su pplementation increased VFA production and the molar proportion of pro pionic acid in these VFA, for starch and sucrose as substrates. Gas pr oduction was higher for maize silage diets than for hay diets, but was not modified by lipid supplementation. Forage source and oil suppleme ntation did not affect ammonia nitrogen uptake by bacteria and efficie ncy of microbial synthesis. These results differ from in vivo results obtained in a previous study utilizing the same diets. These differenc e could be caused by different fermentation conditions between in vivo and in vitro.