Metabolic and endocrine profiles of primiparous beef cows grazing native grassland. 1. Relationships between body condition score at calving and metabolic profiles during the transition period

The body condition score (BCS) at calving has been postulated as the main factor in the interaction of nutrition and reproduction in beef-cow ecosystems. The objective of the present study was to analyse the effect of BCS at calving on endocrine and metabolic profiles during the transition period in primiparous Hereford cows (n = 56) grazing native grassland. Cow BCS was registered and plasma insulin, insulin-like growth factor-I (IGF-I) and metabolites (concentrations of urea, albumin, cholesterol, total protein, non-esterified fatty acids (NEFA)) were determined in plasma from –30 to +45 days postpartum (DPP). The effect of BCS at calving (low ≤3.5 and moderate ≥4; 1–8 visual scale) on BCS evolution and hormone and metabolite concentrations were analysed using a time repeated-measures analysis. Cow BCS, NEFA, urea and IGF-I profiles were affected (P < 0.05) by the BCS at calving and DPP interaction, while insulin tended (P = 0.06) to be affected only by BCS at calving. The low-BCS cows presented a smaller loss of BCS during the prepartum than did moderate-BCS cows, and a delayed BCS recovery during the postpartum. The increase in plasma NEFA was greater (P < 0.05) and started earlier during the prepartum period in the low-BCS cows. Protein concentrations increased during prepartum to +30 DPP, while albumin and urea concentrations were maintained until calving and decreased during the postpartum. Urea concentrations were greater (P < 0.05) during prepartum in low-BCS cows. Concentrations of IGF-I and insulin were greater (P < 0.05) in moderate- than low-BCS cows during prepartum, but did not differ between the groups after calving. No effects were observed in calf weight or milk production at +45 DPP. The association between BCS during prepartum and at calving with the endocrine and metabolic profiles (positive: insulin, IGF-I; negative: NEFA and urea) reflected a better nutritional status and plasticity to negative energy balance on moderate cows. This different endocrine milieu did not affect calf weight and/or milk production. In conclusion, the BCS at calving affected the metabolic and endocrine profile during the transition period of primiparous beef cows grazing native grassland.