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 as signed 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% gras sland hay and 40% production concentrate (diet H), and of 65% corn sil age, 28% production concentrate and 7% soybean meal (diet S). Each die t was also supplied with 7% rapeseed oil. These supplemented diets are designated respectively HO and SO. Digestibility of organic matter wa s 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. Thes e results are consistent with variations in VFA concentration and comp osition. However. differences among diets in in situ cellulose degrada tion were lower than expected. Starch and nitrogen degradation measure d in situ, and ruminal outflow rate of liquid and solids were not modi fied by lipid supply. Hydrogenation of linoleic and linolenic acids wa s high (mean 88.9 and 89.5%, respectively) and did not depend on the d iet.