| Popis: |
This study was designed to estimate genetic parameters for the following traits of Brahman cattle in Brazil: age at first calving (AFC), calving interval (CI), rebreeding (REB), and stayability (STAY). For REB, the value 1 was assigned to heifers that rebred and calved after first calving and the value 0 was assigned to heifers that failed to rebreed after first calving. Likewise, for STAY, the value 1 was assigned to cows that calved at least 3 times by the time they reach 6 yr of age; otherwise, the value 0 was assigned. A bivariate analysis was used to estimate covariances components by using linear animal model for CI and AFC and threshold animal model for REB and STAY. The mean h(2) were 0.10, 0.02, 0.22, and 0.10 for AFC, CI, REB, and STAY, respectively. The genetic correlations were –0.13 between AFC and CI, –0.35 between AFC and REB, –0.57 between AFC and STAY, and 0.32 between REB and STAY, which reveal that cows that remain productive for longer periods in the herd also start breeding younger and present greater chances to REB. The selection of Brahman cattle for reproductive traits, such as AFC, CI, REB, and STAY, will render low magnitude and long-term responses. |
