EFFECT OF LIPID SUPPLY ON IN-VIVO DIGESTION IN COWS - COMPARISON OF HAY AND CORN-SILAGE DIETS

Four Holstein x Friesian cows with rumen and duodenal cannulae were assigned to a 4 x 4 Latin square design consisting of four experimental diets differing in the nature of forage and the presence or absence of rapeseed oil supplement. Dietary treatments were composed of 60% grassland hay and 40% production concentrate (diet H), and of 65% corn silage, 28% production concentrate and 7% soybean meal (diet S). Each diet was also supplied with 7% rapeseed oil. These supplemented diets are designated respectively HO and SO. Digestibility of organic matter was 69.0. 67.5, 73.6 and 70.0% for diets H, HO, S and SO, respectively. The differences were mainly due to variations in NDF digestibility: 55.0, 50.4. 56.9 and 46.9% for diets H, HO, S and SO, respectively. These results are consistent with variations in VFA concentration and composition. However. differences among diets in in situ cellulose degradation were lower than expected. Starch and nitrogen degradation measured in situ, and ruminal outflow rate of liquid and solids were not modified by lipid supply. Hydrogenation of linoleic and linolenic acids was high (mean 88.9 and 89.5%, respectively) and did not depend on the diet.