Effects of dietary fat supplementation and recombinant bovine somatotropin on milk production, nutritional status and lipid metabolism of dairy cows

Abstract

Sixty dairy cows were used to evaluate the effect on performance, metabolism and liver function of adding dietary fat during early lactation (weeks 3–15 postpartum) and injecting recombinant bovine somatotropin (rbST) over the entire lactation. Fat was added to an 18% protein concentrate that was offered in a 1:1 ratio of haylage:concentrate and fed as a total mixed ration. Corn in the control (CRT) concentrate was exchanged for either 2.5% animal fat (AFA), 2.5% Megalac™ calcium salts of fatty acids (CSFA) (ML1), 2.5% Purina CSFA (RP1) or 5% Purina CSFA (RP2). RbST treatment consisted of a subcutaneous injection of either a placebo, 10.3 mg rbST daily or 350 mg rbST every 14 d. Fat-corrected milk production was higher (P < 0.05) in RP2-fed cows than CTR-fed cows and higher for cows injected with rbST daily than in those injected biweekly. Plasma-urea nitrogen and insulin concentrations were lower in RP2-fed cows than in CTR-fed cows and were also lower in rbST-injected cows than in placebo-injected cows (P < 0.05). Plasma triglyceride (TG) and cholesterol concentrations, but not non-esterified fatty acid and phospholipid concentrations, were higher (P < 0.05) in RP2-fed cows than in CTR-fed cows. CSFA supplementation increased C16:0 of the plasma TG fraction and decreased that of C18:0. Dietary fat supplementation did not affect hepatic lipid composition, but liver-TG concentration increased (P < 0.05) with rbST injections. Dietary fat supplementation together with somatotropin injections did not change production parameters from those found with fat supplementation or somatotropin alone. Key words: Dietary fat, dairy cows, bovine somatotropin, lipids