S. I. Araújo

Estimates of genetic parameters of growth traits of Nellore cattle in the Midwest region of Brazil.

Registros de peso ao nascer (PN) e pesos padronizados para 210 (P210); 365 (P365) e 550 (P550) dias de idade na raca Nelore foram usados com o objetivo de estimar componentes de variância dos efeitos geneticos e predicao de valores geneticos dos reprodutores. O modelo incluiu os efeitos fixos de grupo contemporâneo e idade da vaca ao parto, como covariavel, alem dos efeitos aleatorios genetico aditivo direto e genetico materno, de ambiente permanente materno e ambiente temporario. As estimativas das medias e desvios-padrao para PN; P210; P365 e P550 foram iguais a 32,76 ± 3,74; 184,30 ± 29,02; 240,31 ± 41,85 e 322,12 ± 60,77, respectivamente. Em todos os pesos, verificou-se consideravel variabilidade genetica aditiva. A variância de ambiente permanente materno apresentou maior relevância sobre o peso a desmama, sendo praticamente inexistente apos o desmame. Para a variância genetica materna, a estimativa para o peso ao nascer foi mais significativa quando comparada com o peso a desmama. Os valores estimados de herdabilidade para PN; P210; P365 e P550 foram iguais a 0,37 ± 0,02; 0,36 ± 0,03; 031 ± 0,01 e 0,38 ± 0,02, respectivamente. As correlacoes geneticas entre peso ao nascer e outros pesos foram de baixa magnitude, com altos valores dos pesos em outras idades. O uso de reprodutores de maior valor genetico para o efeito materno total permite utilizar reprodutores mais positivos para peso ao desmame e tambem para o ano e peso ao sobreano.

Use of orthogonal functions in random regression models in describing genetic variance in Nellore cattle

A total of 204,912 records of birth weights up to 550 days of age, of 24,890 Nellore cattle, offspring of 375 sires and 16,917 dams from five herds in the state of Mato Grosso, Brazil, were used in order to describe the variability of the weight development by random regression models. The model evaluated as the most suitable used the covariance function of fourth order to describe the variability of the effects of additive genetic, animal permanent environmental and maternal effects of third order to describe the maternal genetic effect, with four classes of residual variance. Heritability estimates ranged from 0.18 to 0.46 from the beginning of trajectory to 210 days of age, from 0.45 to 0.48 post-weaning to 365 days of age and from 0.47 to 0.57 at later ages. The values of additive genetic correlations for different ages showed higher estimates between the closest ages, while birth weight was not very related to the weights at older ages. The body weight performance of the animals has additive genetic variation to respond to selection.

Modelos de regressão aleatória para características de crescimento de bovinos da raça Nelore do estado de Mato Grosso

In this study 138,976 records of live weight between 60 to 610 days of age, from 27,327 Nellore cattle breed, from herds in Mato Grosso State were used in order to describe the genetic variability and to estimate genetic parameters for the live weight at different ages, using random regression models. The model included the fixed effects of contemporary group and age of cow at calving as covariate, random effects of direct additive genetic, maternal genetic, animal and maternal permanent environmental and temporary environment effect. The most appropriate random regression model employed the covariance function with fourth order polynomials to describe the variability of all effects and two residual variance classes. Estimates of direct additive genetic variance and animal permanent environment increased with the age of the animals. Maternal genetic variances and maternal permanent environment exhibited similar behavior, with higher values in pre weaning. The estimated heritability coefficients ranged from 0.25 to 0.43, with higher values at older ages in the growth trajectory of the animals. These results showed the presence of sufficient genetic variability to obtain significant genetic gain through selection, especially after weaning. The results for the direct additive genetic correlation exhibited low correlations between weights in initial and final ages, however, highly correlated weights between nearest ages. Genetic correlation estimates between weaning with weights up to 610 days of age were high and positive and indicate that most of the genes responsible for higher weights in this period are the same.