2010-Boligon_et_al - Covariance functions for body weight...

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A. A. Boligon, M. E. Z. Mercadante, S. Forni, R. B. Lôbo and L. G. Albuquerque Covariance functions for body weight from birth to maturity in Nellore cows doi: 10.2527/jas.2008-1511 originally published online Nov 6, 2009; 2010.88:849-859. J Anim Sci http://jas.fass.org/cgi/content/full/88/3/849 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by on March 5, 2011. jas.fass.org Downloaded from
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ABSTRACT: The objective of this study was to es- timate (co)variance functions using random regression models on Legendre polynomials for the analysis of re- peated measures of BW from birth to adult age. A to- tal 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 ef- fects, and orthogonal Legendre polynomials of animal age (cubic regression) were considered as random co- variables. 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 ani- mal permanent environmental effects, respectively, and third-order polynomials for maternal genetic and ma- ternal permanent environmental effects were the best. Estimates of (co)variance obtained with the multi-trait and random regression models were similar. Direct her- itability estimates obtained with the random regression models followed a trend similar to that obtained with the multi-trait model. The largest estimates of mater- nal 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. Key words: growth curve, longitudinal data, Nellore cattle, random regression ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:849–859 doi:10.2527/jas.2008-1511 INTRODUCTION The growth trajectory of beef cattle can be repre- sented by points that associate BW with age. Body weights obtained along a time scale can be evaluated using random regression models. These models have some advantages over traditional multi-trait models [e.g., allow the inclusion of records that would normally be discarded; Meyer (2004)], describe in a continuous manner the structure of covariances over time, and al- low the estimation of breeding values for a trait at any age within the data interval (Albuquerque and Meyer, 2001; Tier and Meyer, 2004).
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