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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #310016

Title: Genetic effects on birth weight in reciprocal Brahman-Simmental crossbred calves

item DILLON, JASMINE - Texas A&M University
item RILEY, DAVID - Texas A&M University
item HERRING, ANDY - Texas A&M University
item SANDERS, JAMES - Texas A&M University
item Thallman, Richard - Mark

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2014
Publication Date: 2/1/2015
Citation: Dillon, J.A., Riley, D.G., Herring, A.D., Sanders, J.O., Thallman, R.M. 2015. Genetic effects on birth weight in reciprocal Brahman-Simmental crossbred calves. Journal of Animal Science. 93(2):553-561.

Interpretive Summary: It has been routinely observed that calves sired by Brahman (Bos indicus, humped) bulls out of Bos taurus (non-humped) cattle are lighter at birth than calves (of similar breed percentages) that are sired by the same Bos taurus breed of bull and out of Brahman cows. These matings are referred to as reciprocal cross F1 matings. Differences between these reciprocal crosses have traditionally been assumed due to classical maternal effects (e.g., uterine blood flow or nutrient content). Consequently, the default assumption was that calves produced by transfer of embryos to comparable recipient cows would have the same average birth weight. However, we show that reciprocal crosses produced by embryo transfer have differences in birth weight in the same direction and of approximately the same magnitude as those in reciprocal crosses born to their natural dams. Furthermore, sexual dimorphism (the differences between male and female calves) for birth weight was also quite different between reciprocal crosses, whether produced by embryo transfer or not. Male calves were much heavier than females when sired by Brahman sires out of Simmental dams, while the females were the same or slightly heavier than males in the reciprocal cross. A number of genetic models that could potentially explain such differences (but that are not typically included in genetic analysis of beef cattle data) were evaluated. It appears most likely that genes on the X chromosome account for part of the reciprocal differences. Genes that are expressed from only the chromosome inherited from the dam (and/or genes that are expressed from only the chromosome inherited from the sire) seem to be responsible for much of the remaining reciprocal difference. Better understanding of these atypical genetic mechanisms should improve genetic evaluation and selection of Brahman-influence breeds and improve the design of Brahman-influenced breeds, composites, and crossbreeding systems.

Technical Abstract: Brahman cross calves exhibit unusual inheritance of birth weight: Brahman-sired crossbreds out of Bos taurus females are heavier with greater difference between sexes than calves of the reciprocal cross. The objectives of this work were to confirm that unusual inheritance and to investigate non-Mendelian genetic effects that may influence differences in Brahman × Simmental crossbred calves. Crossbred calves were produced by embryo transfer (n = 2,862) and natural service or artificial insemination (n = 2,125) from 1983 to 1991 by a private seedstock producer. Brahman-sired F1 embryos out of Simmental donor cows weighed 9.4 ± 1.1 (P < 0.0001) kg more at birth than Simmental-sired F1 embryos out of Brahman donor cows when transferred to comparable recipients. This reciprocal difference was accompanied by sexual dimorphism: within Brahman-sired F1 calves, males were 5.0 ± 1.4 kg heavier than females, whereas within Simmental-sired F1 calves, females were 0.7 ± 0.5 kg heavier than males. Covariates were constructed from the pedigree to represent genetic effects: proportion Brahman in calves and dams (direct and maternal breed effects), direct and maternal breed heterozygosity, probability of Brahman mitochondrial origin, probability of Brahman Y chromosome, probability of Brahman X chromosome, genomic imprinting (the difference between the probabilities of Brahman in the genetic dam and in the sire), non-random X inactivation by breed of origin (the probability of breed heterozygosity of the X chromosomes of a female), and non-random X inactivation by parent of origin (the difference between probabilities of a female inheriting a paternal or maternal Brahman X chromosome). The maternal breed heterozygosity, genomic imprinting, probability of Brahman X chromosome, and genomic imprinting × sex effect covariates from the full model were significant with regression coefficients of 1.1 ± 0.5 (P < 0.05), '8.3 ± 2.3 (P < 0.01), '3.5 ± 1.3 (P < 0.01), and '5.3 ± 2.0 (P < 0.01), respectively. Results suggest that sex-specific genomic imprinting may be contributing to the inheritance of birth weight in Bos indicus-Bos taurus crossbred calves, similar to patterns of mouse litter and placental weight in interspecific crosses.