Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

First Advisor

Donald E. Franke

Abstract

Data from a long-term rotational crossbreeding study involving Angus, Brahman, Charolais and Hereford cattle were analyzed to evaluate the importance of maternal effects on birth weight (BWT), weaning weight (WWT) and preweaning average daily gain (ADG) and, to estimate genetic parameters. Six different animal models were fitted for each trait, ranging from a single additive to a maternal animal model allowing for both genetic and environmental maternal effects and a genetic covariance between direct and maternal additive effects. Genetic effects were obtained using a maternal animal model allowing for a maternal additive effect and a direct-maternal additive covariance (Model 4). All analyses were carried out using MTDFREML. Maternal permanent environmental variance were not important, while maternal additive (MGE) and the direct-maternal (co)variances were important for all traits. Ignoring MGE resulted in overestimates of $\sigma \sbsp{\rm A}{2}$ and h$\sbsp{\rm A}{2}$. Direct heritability estimates from Model 4 were.35$\pm$.05,.55$\pm$.07 and.57$\pm$.08 for BWT, WWT and ADG, respectively. For the MGE, the corresponding heritabilities were.14$\pm$.02,.25$\pm$.04 and.30$\pm$.04. The direct-maternal genetic correlations were.26$\pm$.14, $-$.36$\pm$.09 and $-$.49$\pm$.08 for BWT, WWT and ADG, respectively. Charolais had the greatest positive direct additive genetic influences on preweaning growth traits and had the largest positive maternal additive genetic influence on WWT, compared to the Hereford breed. The Brahman had positive direct additive genetic influences for BWT and had negative direct additive influences for ADG, compared to the Hereford breed. Angus had negative direct additive genetic effects and had positive maternal additive genetic effects on preweaning growth traits, compared to the Hereford. Brahman was the only breed having a statistically significant maternal additive effect on BWT compared to Hereford. All breeds exhibited positive maternal additive influences on WWT and ADG over Hereford. All direct heterotic effects were positive, except for Angus-Charolais for BWT. Crossbred calves involving the Brahman were the most productive. Birth weight was not influenced by maternal heterosis, except for Charolais-Hereford maternal heterotic effect. Effects involving the Hereford were the only positive and significant maternal heterotic effects on WWT and ADG.

Pages

107

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