Effects of Fat Supplementation and Chop Length on Milk Composition and Ruminal Fermentation of Cows Fed Diets Containing Alfalfa Silage

摘要

The aim of this study was to evaluate the effect of fat supplementation for enhancing milk conjugated linoleic acid (CLA) in early lactation without affecting ruminal fermentation. 24 Holstein dairy cows were assigned to a completely randomized design employing a 2 × 4 factorial arrangement. Factors were particle size (15 and 25 mm) and two different sources of alfalfa supplemented with and without fat (alfalfa hay; alfalfa hay plus 3% fat; alfalfa silage and alfalfa silage plus 3% fat). The results indicated that fat supplementation had no effect on body condition score, milk yield, feeding behaviour and C18 fatty acids profile of milk. Alfalfa silage with fat increased significantly the amount of C18:1and C18:2 in rumen and milk compared to alfalfa hay with fat. Particle size had no effect on milk yield, C18 fatty acids of milk, ruminal NH3-N and butyrate in the rumen. Dry matter intake, milk fat and acetic acid declined with fat supplementation. Dietary alfalfa silage had significant effect on dry matter intake, milk fat, ruminating time and rumen fermentation. Feeding behaviour decreased with reducing particle size. Results revealed that alfalfa silage with fat increased milk yield enhanced CLA in milk improved blood and ruminal metabolite and maintained higher body weight in Holstein dairy cows.