|Tait Jr, Richard|
|Cushman, Robert - Bob|
|Smith, Timothy - Tim|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2015
Publication Date: 3/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62239
Citation: Tait Jr, R.G., Cushman, R.A., McNeel, A.K., Casas, E., Smith, T.P., Freetly, H.C., Bennett, G.L. 2016. Estimates of epistatic and pleiotropic effects of casein alpha s1 (CSN1S1) and thyroglobulin (TG) genetic markers on beef heifer performance traits enhanced by selection. Journal of Animal Science. 94(3):920-926. doi:10.2527/jas2015-9860.
Interpretive Summary: Genetic markers within casein alpha s1 (CSN1S1) and thyroglobulin (TG) have been previously associated with fatness traits of steers for beef production. Those previous survey studies have often ignored animals with two copies of the rare allele because of low frequency of that genotype. Additionally, these genetic markers have not been evaluated for potential adverse effects on female performance in an extensive beef production system. Multiyear selection to increase the frequency of rare alleles for both genetic markers ensured all 9 genotype combinations (3 CSN1S1 genotypes [2 copies of common allele, heterozygotes, and 2 copies of rare allele] x 3 TG genotypes) could be evaluated for an interaction effect on beef heifer performance traits. The CSN1S1 additive effect was the most significant effect on body weight of heifers before their first breeding season. No effect of CSN1S1 and TG genotype (positive or negative) was identified for puberty, fertility or first calf performance traits. Information about these effects will be important for beef geneticists and producers to develop selection and mating systems to improve beef quality in steers with little concern for adverse effects in the cow herd.
Technical Abstract: 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 two years to equalize CSN1S1 and TG genetic marker frequencies to evaluate the epistatic, pleiotropic effects of these markers on BW, reproduction, and first calf performance traits in replacement beef females. 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. The CSN1S1 × TG genotype effect was significant (P < 0.05) for 11-mo BW, 12-mo BW, and tended to be significant (P = 0.08) for 13-mo BW. Consistently, for all 3 traits the most significant effect amongst 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.