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Estimates of epistatic and pleiotropic effects of casein alpha s1 (CSN1S1) and thyroglobulin (TG) genetic markers on beef heifer performance traits enhanced by selection

Tait Jr., R. G., Cushman, R. A., McNeel, A. K., Casas, E., Smith, T. P. L., Freetly, H. C., Bennett, G. L.
Journal of animal science 2016 v.94 no.3 pp. 920-926
additive effect, alleles, alphaS1-casein, beef, breeding season, calves, calving, epistasis, gene frequency, genetic markers, genotype, heifers, marker-assisted selection, pleiotropy, pregnancy, progeny, puberty, thyroglobulin, weaning
Genetic marker effects and type of inheritance are estimated with poor precision when minor marker allele frequencies are low. A stable composite population (MARC II) was subjected to marker assisted selection for 2 yr to equalize CSN1S1 and TG genetic marker frequencies to evaluate the epistatic and pleiotropic effects of these markers on BW, reproduction, and first calf performance traits in replacement beef females (n = 171) managed under 2 postweaning development protocols. Traits evaluated on the heifers were birth BW, weaning BW, 11-mo BW, 12-mo BW, 13-mo BW, first breeding season pregnancy evaluation BW, first calving season BW, 11-mo puberty, 12-mo puberty, 13-mo puberty, first breeding season pregnancy, and first calf weaning rate. Additionally, heifer’s first calf performance traits of ordinal calving date, first calf birth BW, and first calf weaning BW (with and without age adjustment) were analyzed. Selection to increase minor allele frequencies and balanced sampling across genotype classes enhanced the ability to detect all genetic effects except dominance × dominance epistasis. The CSN1S1 × TG genotype effect was significant (P < 0.05) for 11-mo BW and 12-mo BW and tended to be significant (P = 0.08) for 13-mo BW. Consistently, for all 3 traits, the most significant effect among epistatic CSN1S1 × TG genotype effects was the CSN1S1 additive effect, with the G allele decreasing BW. There were no associations between CSN1S1 × TG genotype and fertility related traits (P ≥ 0.46) in this study. Additionally, there were no CSN1S1 × TG genotype associations with first progeny performance traits (P ≥ 0.14). The large effect of the CSN1S1 additive × TG additive interaction on first calf weaning BW was imprecisely estimated, which may warrant further investigation.