Blood parameters in transition dairy cattle and their effects on milk production

Abstract Text: Circulating metabolites nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA) and cholesterol are commonly used as parameters of negative energy balance (NEB) or ketosis in dairy cows, whereas concentrations of aspartate aminotransferase (AST) indicate the occurrence of hepatic lipidosis. The objective of this study was to evaluate the effects of blood parameters on milk production in pre and postpartum Holstein cows. Blood samples were collected from 197 animals in the prepartum (-14 to -1 d) and 285 animals postpartum (+1 to +14 d) from 30 herds of Parana State, Southern Brazil. At each visit, a sample of 10 mL of blood was collected from the coccygeal vessels into sterile tubes without anticoagulant and kept refrigerated until analysis. After collection, blood samples were centrifuged and the serum was analyzed in an automatic biochemical analyzer using commercial kits for NEFA, BHBA, AST and cholesterol parameters. Milk production was assessed using mature-equivalent 305-d (ME305) milk yield estimated at 100 d in milk. While controlling for body condition score (BCS) and parity, the effects of elevated NEFA, BHBA, and cholesterol concentrations on ME305 milk yield were estimated, with herd as a random effect. The mean values for the prepartum were 0.23 ± 0.21 mmol/L NEFA; 0.46 ± 0.27 mmol/L BHBA; 57.48 ± 16.34 U/L AST; and 84.00 ± 19.14 mg/dL cholesterol. In cows and heifers, ME305 milk yield was decreased (P < 0.05) by 760 kg when prepartum NEFA concentrations were ≥0.33 mEq/L. The mean values in the postpartum group were 0.53 ± 0.40 mmol/L NEFA; 0.64 ± 0.44 mmol/L BHBA; 85.17 ± 31.50 U/L AST; and 84.35 ± 23.45 mg/dL cholesterol. In this postpartum group, NEFA and BHBA were (r=0.49; P < 0.01) correlated among themselves and with AST (r=0.31 and r=0.27, respectively; P < 0.01). In all animals sampled postpartum, ME305 milk yield was increased (P < 0.05) by 852 kg when BHBA concentrations were ≥ 0.97 mmol/L. In primiparous and multiparous sampled postpartum, ME305 milk yield was increased by 492 and 1376 kg on hypercholesterolemic animals (> 120 mg/dL), compared with normocholesterolemic (between 80 and 120 mg/dL) and hypocholesterolemic animals (< 80 mg/dL), respectively. In cows sampled postpartum, ME305 milk yield was decreased (P < 0.05) by 793 kg when NEFA concentrations were ≥ 0.72 mEq/L. This study suggests that increased concentrations of NEFA and lower concentrations of cholesterol and BHBA had detrimental effects on milk production.

Keywords: ß-hydroxybutyrate, cholesterol, nonesterified fatty acids