Genetic selection of Nellore cattle raised in tropical areas: Economic indexes and breeding decisions risks

Abstract

Different selection indexes (Index I [Optimal], Index II [Maternal], and Index III [Terminal]) were evaluated in a full-cycle, pasture-based production system of Nellore cattle. The economic selection indexes consisted of combinations of the traits: body weight at 120 (W120), 210 (W210), 365 (W365), and 450 days (W450) of age; age at first calving (AFC); calving interval (CI); scrotal circumference at 365 (SC365) and 450 (SC450) days of age; ribeye area (REA); subcutaneous fat thickness (FAT); stayability (STAY); and accumulated productivity (ACP). Bootstrap analyses were performed to assess the distribution of the response to the optimal index by changes in the economic value of traits and the impact caused by each economic trait. The implementation of the optimal index and the adjustment of the expected return for uncertainty in the prediction of breeding values were carried out with 67 sires. The most genetic-economic important traits were W450, AFC, ACP, and REA. Index I showed the greatest economic response to selection (R$ 938.95/generation), followed by Indexes II (R$ 811.84) and III (R$ 476.26). Economic response variations of Index I ranged from R$ 100.71 to R$ 1747.43. The highest contributions and range of economic response were observed in ACP, followed by W450, and CI. Sires ranking changed ± 4.0 positions with adjustment for risk in Index I, indicating changes in breeding decisions when selecting sires. All indexes presented great efficiency and can be adapted to similar production scenarios that expect a similar overall gain. Adjustment for risk in the selection index should be considered for optimal breeding decisions.