Gestation length and growth performance in beef heifers: comparative analysis of genetic groups during first pregnancy.

For the planning of breeding activities in beef cattle production, it is essential to understand the gestation length of the dams, which varies according to genetic group and influences weight gain. The objectives of this study were: (a) to evaluate the gestation length in heifers from different genetic groups; (b) to assess body weight gain in heifers from different genetic groups from conception to calving, and (c) to evaluate body weight at first calving. This study was conducted on a commercial farm in the state of Mato Grosso do Sul, Brazil. Three genetic groups were evaluated: (1) Angus (n = 181); (2) Brangus (n = 125), and (3) Nellore (n = 96), with an initial age of 19 ± 6 months and an average body weight of 291 kg under a pasture-based production system. All heifers were weighed at the beginning of the breeding season, and inseminated. After calving, they were weighed again. Angus heifers had the shortest gestation length (282 days), whereas Nellore heifers had the longest (295 days) (p < 0.01). Angus heifers also had the lowest body weight gain from conception to calving (p < 0.01) and, consequently, the lowest body weight compared to Brangus and Nellore heifers. This study concludes that the reproductive parameters of beef heifers vary according to genetic group. These differences should guide genetic selection, help define minimum weights for first breeding, and the breeding season length to improve efficiency in beef production.