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Estimation of genetic parameters for average daily gain using models with competition effects

C. Y. Chen^*, S. D. Kachman , R. K. Johnson^*, S. Newman and L. D. Van Vleck

^* Department of Animal Science, University of Nebraska, Lincoln, NE 68583-0908 , Department of Statistics, University of Nebraska, Lincoln, NE 68583-0963 , Genus – PIC NA, Hendersonville, TN 37075 Roman L. Hruska U.S. Meat Animal Research Center, ARS-USDA, Lincoln, NE 68583-0908

lvanvleck{at}unlnotes.unl.edu

Abstract

Components of variance for ADG with models including competition effects were estimated from data provided by Pig Improvement Company on 11,235 pigs from 4 selected lines of swine. Fifteen pigs with average age of 71 d were randomly assigned to a pen by line and sex and taken off test after approximately 89 d (off-test weights ranged from 61 to 158 kg). Models included fixed effects of line, sex, and contemporary group, with random direct genetic, competition (genetic and environmental), pen, litter, and residual effects. With the full model, variances due to direct, direct-competition, genetic competition, and litter (co)variance components could be partitioned; genetic competition variance was small, but statistically significantly different from zero. Variances due to environmental competition, pen, and residual effects could not be partitioned, but combinations of these environmental variances were estimable. Variances could be partitioned with either pen effects or environmental competition effects in the model. Environmental competition effects seemed to be the source of variance associated with pens. With pen as a fixed effect and without environmental competition effects in the model, genetic components of variance could not be partitioned, but combinations of genetic (co)variances were estimable. With both pen and environmental competition effects ignored, estimates of direct-competition and genetic competition (co)variance components were greatly inflated. With competition (genetic and environmental) effects ignored, the estimate of pen variance increased by 39% with little change in estimates of direct genetic or residual variance. When both pen and competition (genetic and environmental) effects were dropped from the model, variance due to direct genetic effects was inflated. Estimates of variance due to competition effects were small in this study. Including environmental competition effects as permanent environmental effects in the model did not change estimates of genetic (co)variances. We conclude that including either pen effects or environmental competition effects as random effects in the model avoids bias in estimates of genetic variances, but including pen effects is much easier.

Key Words: competition • genetic parameters • swine

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