Estudo genético-quantitativo de características de crescimento, reprodução, carcaça e escores visuais em um rebanho nelore sob seleção para precocidade sexual
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2017-02-23
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Universidade Federal de Goiás
Resumo
The reproductive efficiency in cattle herds, as well as the anticipation of puberty, has positive
effects on zootechnical indexes and on the profitability of production systems. Thus, the aim
of this study was to estimate the genetic parameters and the genetic and phenotypic trends for
growth, carcass, and reproductive traits in a Nellore cattle herd under selection for sexual
precocity, given age at first conception and age at first calving as selection criterion.
Furthermore, this study also aimed to evaluate, using multivariate analyzes, which traits,
among growth, carcass and visual scores, better discern early pregnancy. Genetic parameters
were estimated for birth weight (BW), weight at 120 (W120), 210 (W210), 365 (W365) and
450 (W450) days of age, average daily gain pre-weaning and post-weaning (ADGPRE e
ADGPOS), rib eye area (REA), backfat thickness (BF), rump fat thickness (RF), marbling
(MAR), hot carcass weight (HCW), weight of edible portion (WEP), scrotal circumference at
365 (SC365) and 450 (SC450) days of age, gestation length (LG), days open (DO), calving
interval (CI), real fertility (RF), cumulative productivity (CP), relation to weaning (RW), age
at first conception (AFCo) and age at first calving (AFCa). Data were provided by Vera Cruz
Ranch and the National Association of Breeders and Researchers (ANCP). The covariance
components were estimated using the Restricted Maximum Likelihood method, available on
BLUPF90 package, in univariate and bivariate analyzes using animal model. The heritability
estimated for BW (0.39), W120 (0.32), W210 (0.31), W365 (0.33), W450 (0.34), ADGPRE
(0.23), ADGPOS (0.27), REA (0.39), BF (0.34), RF (0.34), MAR (0.38), HCW (0.39), WEP
(0.39), SC365 (0.33), SC450 (0.33), LG (0.23), DO (0.34), CI (0.23), RF (0.21), CP (0.25),
RW (0.26), AFCo (0.21) and AFCa (0.24) indicated the possibility of genetic selection. The
maternal heritability estimated for BW (0.06), W120 (0.08), W210 (0.07), W365 (0.05),
W450 (0.11), ADGPRE (0.12), ADGPOS (0.08), SC365 (0.07) and SC450 (0.03) indicated
genetic effects of the dam on the progeny performance, until the post-weaning phase, for
growth traits. The genetic correlations estimated within growth traits, between growth and
carcass traits, within carcass traits and reproductive trait were favorable and of moderate
magnitude. The traits that indicate sexual precocity showed genetic correlation coefficients
ranging from -0.51 to -0.15, -0.62 to -0.33 and -0.61 to 0.14, between growth, carcass and
reproductive traits, respectively. Genetic correlation coefficients were, in most cases,
favorable. The genetic trends obtained showed, in general, the effectiveness of the adopted
selection criteria with satisfactory genetic gains. Selection for sexual precocity, based on age
at first conception, shall promote opposite direction genetic changes on growth, carcass and
reproductive traits, which is the desirable effect. Birth weight, fat thickness, bone structure,
musculature, rib depth, tail and rump insertion were the traits that presented greater
discrimination power for early pregnancy. Thus, these traits can be used as such management
targeting criteria and decision-making practices, in order to enable animals to express early
pregnancy, guiding the breeders in selecting females for sexual precocity.
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BRUNES, L. C. Estudo genético-quantitativo de características de crescimento, reprodução, carcaça e escores visuais em um rebanho nelore sob seleção para precocidade sexual. 2017. 190 f. Dissertação (Mestrado em Zootecnia) - Universidade Federal de Goiás, Goiânia, 2017.