Associação genética da prenhez aos 16 meses com o peso à desmama e o ganho de peso em animais da raça Nelore

Abstract

RESUMO -Objetivou-se verificar a possibilidade de utilização da prenhez de novilhas aos 16 meses (Pr16) como critério de seleção e as possíveis associações genéticas entre prenhez em novilhas aos 16 meses e o peso à desmama (PD) e o ganho de peso médio da desmama ao sobreano (GP). Foram realizadas análises uni e bicaracterísticas para estimação dos componentes de co-variância, empregando-se um modelo animal linear para peso à desmama e ganho de peso da desmama ao sobreano e não-linear para Pr16. A estimação dos componentes de variância e da predição dos valores genéticos dos animais foi realizada por Inferência Bayesiana. Distribuições "flat" foram utilizadas para todos os componentes de covariância. As estimativas de herdabilidade direta para Pr16, PD e GP foram 0,50; 0,24 e 0,15, respectivamente, e a estimativa de herdabilidade materna para o PD, de 0,07. As correlações genéticas foram -0,25 e 0,09 entre Pr16, PD e GP, respectivamente, e a correlação genética entre Pr16 e o efeito genético materno do PD, de 0,29. A herdabilidade da prenhez aos 16 meses indica que essa característica pode ser utilizada como critério de seleção. As correlações genéticas estimadas indicam que a seleção por animais mais pesados à desmama, a longo prazo, pode diminuir a ocorrência de prenhez aos 16 meses de idade. Além disso, a seleção para maior habilidade materna favorece a seleção de animais mais precoces. No entanto, a seleção para ganho de peso da desmama ao sobreano não leva a mudanças genéticas na precocidade sexual em fêmeas.Palavras-chave: bovino de corte, inferência bayesiana, precocidade sexual Genetic associations of heifer pregnancy at 16 months with weaning weight and average daily gain from weaning to yearling in Nellore cattleABSTRACT -The objective of the present study was to determine the possible use of heifer pregnancy at 16 months (HP16) as a selection criterion and its possible genetic associations with weaning weight (WW) and average daily gain from weaning to yearling (ADGWY). Covariance components were estimated by uni and bivariate animal models assuming a linear model for weaning weight and average daily gain from weaning to yearling and a nonlinear for HP16. Variance components and breeding values were estimated using Bayesian inference. Flat distributions were used for all (co)variance components and genetic correlations. The estimates of heritability direct for HP16, WW and ADGWY were 0.50; 0.24 and 0.15; respectively. And the maternal heritability estimate for the WW was 0.07; The genetic correlations were -0.25 and 0.09; between HP16, WW and ADGWY, respectively; and the genetic correlation between HP16 and maternal effects of WW was 0.29. The heritability estimate of heifer pregnancy at 16 months indicated that the trait can be used as a selection criterion. The genetic correlation estimates indicated that the selection for heavier animals at weaning, in the long-term, could decrease the occurrence of heifer pregnancy at 16 months. Moreover, the selection for animals with greater maternal ability can...

Genetic parameters and relationships of heifer pregnancy and age at first calving with weight gain, yearling and mature weight in Nelore cattle

“…Thus, the selection based only in WG and/or YW will not satisfactorily improve the ability of females to conceive at 16 months of age. Using another sample of the same data from the present study, Shiotsuki et al (2009) found low and positive genetic correlations of HP16 with post-weaning gain (0.09 ± 0.05) and negative with weaning weight (−0.25 ± 0.03). However, no similar studies were found in the literature using different populations, to allow a fair comparison.…”

“…Few studies on beef cattle have investigated genetic associations of heifer pregnancy or age at first calving with body weight (Boligon et al, 2010;Grossi et al, 2009;Shiotsuki et al, 2009). Currently, in most of Brazilian cattle ranches, an increase in females mature weight is undesirable since larger animals have higher maintenance requirements and lower reproduction rates in environments where feed availability is limited and with low nutritional value (Beretta et al, 2002;Kaps et al, 1999).…”

Generalized linear mixed models for the genetic evaluation of binary reproductive traits: a simulation study

“…Since the percentages of precocious females adopted in the simulation did not include the value of 50%, the best results were reported for the closest percentage, i.e., 30%. The values adopted here were chosen according to previous studies involving Nellore cattle (Eler et al, 2002;Eler et al, 2004;Silva et al, 2005;Pereira et al, 2007;Shiotsuki et al, 2009). The percentages of animals coinciding with the TOP10 bulls obtained with the logit/probit and probit/logit models were lower than those obtained with the probit/probit and logit/logit models (Table 5).…”

“…The link function for binary data most widely used in animal breeding is the probit link, also known as the threshold model (Gianola & Foulley, 1983;Abdel-Azim & Berger, 1999;Kadarmideen et al, 2000Kadarmideen et al, , 2001Silva et al, 2005;Shiotsuki et al, 2009) Other functions can also be…”

“…The parametric heritability used in the simulation was 0.40 and reflects the results of recent studies involving Nellore animals, which reported moderate to high estimates (Eler et al, 2002;Eler et al, 2004;Silva et al, 2005;Pereira et al, 2007;Shiotsuki et al, 2009). Different additive genetic variances were employed according to the link function to be used in the analysis of the simulated data.…”