Effect of Supplementation on the Productive and Reproductive Performance of Nellore Heifers Grazing Mombasa Grass Pasture in Different Seasons

The objective was to evaluate the effect of supplementation during three seasons (autumn, winter, and spring) on the productive and reproductive performance of Nellore heifers grazing on Mombaça grass. A total of 28 Nellore heifers were subjected to two supplementation strategies: 15 CP [15% crude protein (CP)] and 18 CP (18% CP). The experimental design was completely randomized in a factorial arrangement (two supplementation strategies and three seasons). A strategy × season interaction effect was observed for height (p = 0.008), with the 15 CP strategy in spring showing a higher average (56 cm) compared to 18 CP (26 cm). Regarding pasture chemical composition, the season significantly influenced quality (p < 0.05), with winter presenting inferior quality. A strategy × season interaction effect was also observed (p < 0.05), with lower averages recorded during winter for the 18 CP strategy in final body weight (FBW) (271.74 kg), total weight gain (TWG) (31.48 kg), and stocking rate (SR) (3.99 animal units per hectare, AU/ha). In reproductive efficiency, the 15 CP strategy achieved a pregnancy rate of 85% compared to 54% for the 18 CP strategy. The 15 CP strategy provided better performance for the heifers, increasing FBW, TWG, SR, and pregnancy rate, with significant results in spring due to improved forage quantity and quality associated with supplementation.