Estimation of heterotic effects on stayability in beef cattle

Huff, Emma, author
Enns, R. Mark, advisor
Speidel, Scott, committee member
Holt, Timothy, committee member
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Stayability in beef cattle is defined as the probability that a cow remains in the herd until age six given that she has calved as a heifer. In some breeds with total herd reporting, those cows are required to calve every year. Stayability influences herd profitability by decreasing the need for replacements by increasing the number of cows that reach the typical breakeven age of six. Stayability is a binary trait on the observed scale and is considered a lowly heritable trait. General consensus is that lowly heritable traits should be subject to higher levels of heterosis in crossbreeding programs. Therefore, heterosis should have a positive effect on the cows' ability to remain in the herd until age six. The objective was to estimate maternal and individual heterosis values for stayability. Data was obtained from the American Gelbvieh Association and included a total of 13,114 animals, with 5 being purebred American Angus and 5,493 purebred Gelbvieh, and the rest being a combination of crossbred animals. Variance components and fixed heterosis effects were estimated from single trait animal models using a probit threshold link function. The model included contemporary group as a fixed effect and breed percentage as a linear covariate. Two models were evaluated with different heterosis covariates, model one included only individual heterosis and model two included individual and maternal heterosis. Heterosis was estimated to be 48.96% when individual heterosis is 100% with the first model. For the second model 100% individual heterosis was estimated to be 48.88% and 49.57% was the estimate for 100% maternal heterosis. The results from this experiment indicate that stayability is affected by heterosis and that these effects should be accounted for in cattle evaluation using pure and crossbred data.
2019 Spring.
Includes bibliographical references.
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