Effects of biostimulation and nutritional supplementation on pubertal age and pregnancy rates of Nelore heifers (Bos indicus) in a tropical environment

To determine effects of biostimulation (BIO) and dietary supplementation (BIO + S) on pubertal age and pregnancy rates, Nelore heifers (n = 392) were randomly assigned to one of four treatment groups (n = 98/group). All animals were in tropical environmental conditions, in the middle-west region of Brazil, grazing in pastures of Brachiaria brizantha, cv. Marandu; Panicum Maximum, cv. Tanzânia and Brachiaria humidícula. The heifers of the BIO group were kept in the presence of bulls while being maintained on pasture; the animals in the BIO + S group were kept in the presence of bulls while being managed on pasture and were fed a diet with greater energy and protein content to produce 0.49 kg of BW gain/day; the animals in control group (the NBIO) were kept away from bulls and under pasture conditions; and the animals in the NBIO + S group were kept away from bulls, were maintained on pasture, and were fed the same diet as the BIO + S group. Heifers were bred at 22–23 months of age, and pregnancy diagnosis was made 45 days after the end of the breeding season. There were differences (P < 0.05) between groups regarding pubertal heifers up to 19 months (NPH), final body weight (FBW) and pregnancy rates (P < 0.01), with an advantage for the animals in the BIO and BIO + S groups. Although the effect of a diet with greater protein and energy content was not clear in this experiment, the exposure of heifers to a male during the prepubertal period decreased age at the first breeding season, resulting in a significant reduction in age of first pregnancy in Nelore heifers kept under extensive management systems in a tropical environment.