Nutritional strategies for heifers under grazing system: productive and nutritional performance, metabolic profile and ovarian activity

The objective of this study was to evaluate the effects of nutritional strategies on productive and nutritional performance, metabolic profile, and ovarian activity in heifers under grazing in the tropics in Brazil. Forty Nellore heifers averaging 8.5 ± 0.06 months and 248.6 ± 3.3 kg body weight (BW) were distributed in a completely randomized 2 × 2 factorial design with four treatments and ten replicates. The evaluated strategies consisted of different amounts of energetic-protein supplement: (1) 4 g/kg of BW of supplement in the pre-weaning and post-weaning; (2) 4 g/kg of BW of supplement pre-weaning and 6 g/kg in the post-weaning; (3) 6 g/kg of BW of supplement in the pre-weaning and 4 g/kg of BW in the post-weaning and; (4) 6 g/kg of BW of supplement in the pre-weaning and post-weaning. Crude protein (CP) and organic matter (OM) intake were increased ( P < 0.05) by increasing the amounts of supplement in the post-weaning. Additionally, increasing supplement amounts in the post-weaning increased the digestibility of OM and CP ( P < 0.05). Means insulin and glucose concentrations were greater ( P < 0.05) for heifers that received higher amounts of supplement in the post-weaning. Average daily gain and fat thickness in the rump were increased ( P < 0.05) by increasing supplement amounts in the post-weaning. Amounts of supplement did not influence the body growth of heifers. However, follicular number, diameter, and progesterone concentration were greater ( P < 0.05) for heifers that received higher amounts of supplement in the post-weaning. In summary, increasing supplement amounts in the post-weaning improve the performance, energy and metabolic status, and ovarian activity in beef heifers under grazing in the tropics. Due to higher intake of supplement, the heifers receiving 6 g/kg of BW post-weaning had greater responses, independently of the supplement amount received pre-weaning.