Ednira Gleida Marques

Tendência genética para características relacionadas à velocidade de crescimento em bovinos Nelore da região norte do Brasil

The objective was to estimate the (co) variance, genetic parameters and trends for the characteristics, days to gain 160 kg (D160) in the pre-weaning phase, and days to gain 240 kg (D240) in the post-weaning phase, in Nellore cattle, grown in Northern Brazil. Records analyzed were of animals raised on pasture in northern Brazil, provided by the Brazilian Association of Zebu Breeders - ABCZ, and collected from 1997 to 2007. Contemporary groups (herd, year, birth season and gender) were used as a fixed effects model, and age at calving as a covariant. Estimates of (co) variance were obtained using the MTDFREML software. The averages observed for D160 and D240 were 235 ± 46 days and 578 ± 171 days respectively. Estimates of heritability for D160, due to the additive genetic and maternal effect, were 0.27 ± 0.03 and 0.35 ± 0.04, respectively. For D240, the heritability for the additive genetic effect was 0.28 ± 0.03. This indicates that selection for any of the characteristics will result in genetic progress. Potential genetic gains due to the additive genetic effect, were 1.02 and 3.17 days per year for D160 and D240 respectively. This corresponds to 0.43 and 0.55% of the average of days to gain 160 kg (pre-weaning) and 240 kg (post-weaning) respectively. Although weight is currently used as the selection criteria, the genetic trends for D160 and D240 indicated the existence of genetic progress when using these characteristics as the selection criteria.

Índices de seleção para bovinos da raça Nelore participantes de provas de ganho em peso em confinamento

Despite many subjective criteria are still adopted, feedlot bovines are currently selected by weight gain tests according to varied economic traits. Considering this situation, selection indexes are becoming a possibility to select multiple traits simultaneously in genetic breeding programs. Thus, this study was carried out to investigate the development of traits measured in weight gain evaluations, to verify empiric index pondered and to suggest selection indexes to classify animals in performance tests. Data analyzed in this study was obtained from 392 weight gain trails in Nellore cattle in feedlot, during 2000 and 2010. The information was supplied by the Brazilian Association of Zebu Breeders – ABCZ. Average daily weight gain, final body weight adjusted to 426 days, scrotal perimeter and EPMURAS were evaluated. The animal predicted breeding value for each trait was carried out using MTDFREML software. Following the selection index composition, a simulation was undertaken using genetic parameters obtained from an original database from the predicted genetic value. In conclusion, by the use of indexes aiming at selection based on final weight it is possible to obtain greater genetic gain.