PROTEIN SUPPLEMENTATION OF HIGH PROTEIN ALFALFA SILAGE FED TO LACTATING DAIRY-COWS

Eight multiparous cows in late lactation were fed alfalfa silage ad libitum twice daily and one of four supplements seven times daily. Supplements differed in level of barley (1.65 kg DM d-1) for the control diet and 2.40 kg DM d-1 for supplemented diets) and source of supplemental protein (control diet: none; blood meal diet: 100% blood meal; blood meal-casein diet: 50% blood meal and 50% casein; casein diet: 100% casein). Silage contributed approximately 90 % of dietary dry matter (DM) in the control diet and about 85 % in supplemented diets. Intake of DM and crude protein (CP) was lower for control than for supplemented diets. Intake of DM, organic matter, neutral detergent fibre and CP all increased linearly as casein replaced blood meal. Rumen concentrations of volatile fatty acids and pH suggested that fermentation was stimulated as casein replaced blood meal. Production of milk, protein and lactose was higher for supplemented cows. Control cows lost 0. 66 kg d-1 of body weight, and this differed from the body weight change for supplemented cows. The overall performance of animals on supplemented diets was judged superior to that of animals on the control diet, and overall performance was also judged to have improved within supplemented diets as casein replaced blood meal. Data collected did not conclusively identify the mechanism for improved performance with casein; however, it seems likely that increased rumen microbial growth and passage to the lower digestive tract improved both energy and protein status.