Metabolic status of crossbred Charolais × Nellore cows throughout the final third of gestation and lactation

Abstract

The objective of this study was to evaluate the metabolic status of beef cows during the final third of gestation and thereafter until the end of the subsequent breeding season. The study was conducted using 30 beef cows, aged between 4 and 11 years, derived from crosses between Charolais and Nellore cattle. To assess the metabolic status of cows, we obtained measurements of body weight and condition (BW and BCS), and complemented these by analyzing the following blood metabolites: total proteins, globulins, albumin, glucose, cholesterol, and triglycerides. Assessments were performed at 95 days pre-calving, and again at 7, 21, 63, and 110 days post-calving. The experimental design was completely randomized with five collection periods and 30 repetitions (cows). The BW of cows was found to be highest at 110 days postpartum (489.1 kg), and loss of BW was observed between 21 and 63 days postpartum (-3.72 kg). The lowest BCS value was recorded after 63 days of lactation (2.85 points). With respect to blood metabolites, concentrations of total proteins were higher at 7 and 110 days postpartum relative to the levels recorded during gestation (8.3 and 8.3 vs. 7.7 g dL-1, respectively), whereas serum globulin levels were higher at 7, 21, and 110 days postpartum relative to those at gestation (5.2, 5.2, and 5.1 vs. 4.8 g dL -1, respectively). Compared with samples obtained during gestation, the highest levels of albumin (P < 0.05) were observed at 7, 63, and 110 days postpartum (3.1, 3.1, and 3.2 vs. 2.9 g dL-1, respectively). Serum glucose was higher during pregnancy and in the first week of lactation relative to the values recorded after 21 and 63 days of lactation (80.9 and 76.7 vs 71.5 and 72.3 mg dL-1, respectively). Moreover, cholesterol concentrations increased with the progression of lactation, with the highest value being recorded at 110 days postpartum (222.1 mg dL-1). Collectively, the findings of this study, indicate that Charolais × Nellore cows raised exclusively on native pasture mobilize body reserves, lose weight, and show a negative energy balance during the first weeks of lactation, with detrimental consequences for subsequent reproductive activity.