2009-Chen_et_al - Effects of social interactions on...

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C. Y. Chen, R. K. Johnson, S. Newman, S. D. Kachman and L. D. Van Vleck of boars Effects of social interactions on empirical responses to selection for average daily gain doi: 10.2527/jas.2008-0937 originally published online November 7, 2008 2009, 87:844-849. J ANIM SCI http://jas.fass.org/content/87/3/844 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on October 11, 2011 jas.fass.org Downloaded from
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ABSTRACT: Effects of social interactions on re- sponses to selection for ADG were examined with re- cords of 9,720 boars from dam lines (1 and 2) and sire lines (3 and 4) provided by Pig Improvement Company. Each line was analyzed separately. Pens contained 15 boars. Average daily gains were measured from about 71 to 161 d of age and BW from 31 to 120 kg. Models included fixed effects of contemporary groups and ini- tial test age as a covariate and random direct genetic (a), social genetic (c), social environmental (ce), and litter (lt) effects. Estimates of direct heritability with model 1 (the full model with a, c, ce, and lt) were 0.21, 0.28, 0.13, and 0.15 for lines 1 to 4. Estimates of heritability of social effects were near zero. Estimates of total heritable variance were 55, 52, 38, and 96% of phenotypic variance for lines 1 through 4. Empirical responses to selection with model 1 were calculated us- ing the parameter estimates from model 1. For response of 1 genetic SD for both components (a and c), the proportions of expected total gain due to social effects (with economic weights of 1 and pen size-1 = 14) were 54, 28, 65, and 65% for the 4 lines. Genetic superiori- ties of the top 10% of boars were calculated for boars ranked using reduced models, but with EBV calculated using the full model (model 1). Average total breeding values (ETBV = EBV a +14EBV c ) for the top 10% of boars selected with model 1 were 74.08, 94.26, 31.79, and 92.88 g for lines 1 through 4, respectively. For rank- ings based on model 2 (a, ce, and lt), but EBV calcu- lated with model 1, average total breeding values for the top 10% were 68.15, 94.03, 7.33, and 84.72 g with empirical correlated responses for genetic social effects from selection for direct effects of 0.93, 1.89, −2.19, and 3.52 g for lines 1 to 4. Key words: response to selection, social interaction, swine ©2009 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2009. 87:844–849 doi:10.2527/jas.2008-0937 INTRODUCTION Current selection programs based on BLUP to pre- dict genetic merit have the assumption of an additive genetic model with no interaction among genotypes. If genetic social effects exist, such an assumption may not be valid and could result in less than expected response to individual selection if selection is based only on direct additive genetic models (Griffing, 1967; Wright, 1986; Muir, 2005). Mixed model equations in- corporating social effects were applied recently to pre- dict genetic gains for individual selection (Muir and Schinckel, 2002). For swine selected on growth and raised in groups, competition with pen mates might affect group performance. Estimates of heritability of social effects appear to be very low in swine (Cassady and Van Vleck, 2004; Arango et al., 2005; Chen et al.,
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2009-Chen_et_al - Effects of social interactions on...

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