Effects of Fat Supplementation and Immature Alfalfa to Concentrate Ratio on Lactation Performance of Dairy Cattle

Abstract

Forty-six multiparous Holstein cows were assigned 5 d postpartum to a completely randomized design employing a 2 × 3 factorial treatment arrangement. Factors were 0 or 5% added prilled fat (DM basis) substituted for shelled corn and alfalfa silage fed in forage-to-concentrate ratios of 45:55, 64:36, and 84:16 (DM basis). Interactions between fat and forage level were not observed for any of the parameters measured. Energy density, calculated using data from a digestibility trial, was similar between 45:55 and 64:36 diets (1.66 Mcal NE1/kg) and was lower with 84:16 diets (1.48 Mcal NE1/kg) for the 100 d trial. Fat supplementation increased energy density of the diets (1.67 vs. 1.53 Mcal NE1/kg). Dry matter digestibility, energy intake, and 4% FCM yields were similar for cows fed 45:55 and 64:36 diets and lower for those fed the 84:16 diets. Fat supplementation did not affect DM digestibility. Dry matter intake declined with increasing forage level and fat supplementation. Milk yield decreased as forage level increased. Fat supplementation did not affect yield of milk or FCM. Milk fat percentage was lower for cows fed 45:55 than 64:36 or 84:16 diets. Fat supplementation increased milk fat percentage. Milk protein yield decreased as forage level increased but was unaffected by fat supplementation. Results suggest higher levels of concentrate support higher milk yields, and prilled fat supplementation improves fat test when fed with immature forages. Prilled fat supplementation did not enhance lactation performance because of depressed DM intake in early lactation.