2009-Forni_et_al - Comparison of different nonlinear...

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S. Forni, M. Piles, A. Blasco, L. Varona, H. N. Oliveira, R. B. Lôbo and L. G. Albuquerque Comparison of different nonlinear functions to describe Nelore cattle growth doi: 10.2527/jas.2008-0845 originally published online Aug 15, 2008; 2009.87:496-506. J Anim Sci http://jas.fass.org/cgi/content/full/87/2/496 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 February 2, 2011. jas.fass.org Downloaded from
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ABSTRACT: This work aims to compare different nonlinear functions for describing the growth curves of Nelore females. The growth curve parameters, their (co)variance components, and environmental and ge- netic effects were estimated jointly through a Bayes- ian hierarchical model. In the first stage of the hierar- chy, 4 nonlinear functions were compared: Brody, Von Bertalanffy, Gompertz, and logistic. The analyses were carried out using 3 different data sets to check good- ness of fit while having animals with few records. Three different assumptions about SD of fitting errors were considered: constancy throughout the trajectory, linear increasing until 3 yr of age and constancy thereafter, and variation following the nonlinear function applied in the first stage of the hierarchy. Comparisons of the overall goodness of fit were based on Akaike informa- tion criterion, the Bayesian information criterion, and the deviance information criterion. Goodness of fit at different points of the growth curve was compared applying the Gelfand’s check function. The posterior means of adult BW ranged from 531.78 to 586.89 kg. Greater estimates of adult BW were observed when the fitting error variance was considered constant along the trajectory. The models were not suitable to describe the SD of fitting errors at the beginning of the growth curve. All functions provided less accurate predictions at the beginning of growth, and predictions were more accurate after 48 mo of age. The prediction of adult BW using nonlinear functions can be accurate when growth curve parameters and their (co) variance components are estimated jointly. The hierarchical model used in the present study can be applied to the prediction of mature BW in herds in which a portion of the animals are culled before adult age. Gompertz, Von Bertalanffy, and Brody functions were adequate to establish mean growth patterns and to predict the adult BW of Nelore females. The Brody model was more accurate in pre- dicting the birth weight of these animals and presented the best overall goodness of fit. Key words: Bayesian analysis, beef cattle, growth curve, longitudinal data, model choice, nonlinear function ©2009 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2009. 87:496–506 doi:10.2527/jas.2008-0845 INTRODUCTION Several studies suggest the Brody function as the most appropriate to describe beef cattle growth, be- cause of its goodness of fit, computational simplicity, interpretability of parameters, and model convergence, even if data are missing (Bullock et al., 1993; Kaps et al., 2000; Arango and Van Vleck, 2002). However,
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This note was uploaded on 01/26/2012 for the course ECON 2272 taught by Professor Gay during the Spring '08 term at Birmingham-Southern College.

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2009-Forni_et_al - Comparison of different nonlinear...

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