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Produção Científica
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08/06/2010
Principios e resultados de pesquisa Científica do Programa Nelore Brasil
Autor:
Raysildo Barbosa Lôbo; Carina Ubirajara de Faria
17/03/2010
Covariance functions for body weight from birth to maturity in Nellore cows
ABSTRACT: The objective of this study was to estimate
(co)variance functions using random regression
models on Legendre polynomials for the analysis of repeated
measures of BW from birth to adult age. A total
of 82,064 records from 8,145 females were analyzed.
Different models were compared. The models included
additive direct and maternal effects, and animal and
maternal permanent environmental effects as random
terms. Contemporary group and dam age at calving
(linear and quadratic effect) were included as fixed effects,
and orthogonal Legendre polynomials of animal
age (cubic regression) were considered as random covariables.
Eight models with polynomials of third to
sixth order were used to describe additive direct and
maternal effects, and animal and maternal permanent
environmental effects. Residual effects were modeled
using 1 (i.e., assuming homogeneity of variances across
all ages) or 5 age classes. The model with 5 classes was
the best to describe the trajectory of residuals along
the growth curve. The model including fourth- and
sixth-order polynomials for additive direct and animal
permanent environmental effects, respectively, and
third-order polynomials for maternal genetic and maternal
permanent environmental effects were the best.
Estimates of (co)variance obtained with the multi-trait
and random regression models were similar. Direct heritability
estimates obtained with the random regression
models followed a trend similar to that obtained with
the multi-trait model. The largest estimates of maternal
heritability were those of BW taken close to 240
d of age. In general, estimates of correlation between
BW from birth to 8 yr of age decreased with increasing
distance between ages.
Autor:
BOLIGON, A.A.; MERCADANTE, M.E.Z.; FORNI, S.; LÔBO, R.B.; ALBUQUERQUE, L.G