Skip to main content
ARS Home » Research » Publications at this Location » Publication #47184
Title: EFFECT OF ACCOUNTING FOR DIFFERENT PHENOTYPIC VARIANCES BY SIRE BREED AND SEX ON SELECTION OF SIRES BASED ON EPDS FOR 200- AND 365-D WEIGHTS

Author
item RODRIGUEZ-ALMEIDA - UNIV OF NEBRASKA
item VAN VLECK L DALE - 5438-01-30
item Cundiff, Larry

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Genetic evaluations that compare bulls of different breeds require estimates of genetic differences between breeds and estimates of genetic values of bulls as differences from the averages of their breeds. The range of estimates of differences within a breed will depend on the genetic and phenotypic variation associated with that breed. Which bulls would be ranked at the top in a comparison of bulls of several breeds depends on th breed means and on the range of differences within a breed. With intense selection, more bulls for a breed with large variation would be selected than from a breed with small variation if the breed means were the same. Differences in magnitude of variation in records of animals of different breeds also may affect estimates of breed differences. This study of MARC data attempted to quantify the effects of differences in variation due to sire breed and sex of calf as compared to not accounting for differences in nvariance. Some changes in estimates of sire breed effects and in predict- ion of expected progeny differences occurred when differences in phenotypic variances for 200- and 365-d weights according to sire breed and sex were accounted for. However, reranking of sires was minimal. The number of sires selected from different breeds changed slightly when heterogeneous phenotypic variances were considered in the model, but potential genetic gain was essentially unchanged.

Technical Abstract: The effects of accounting for different phenotypic variances according to sire breed and sex subclasses on estimation of sire breed effects and prediction of EPDs of sires mated to Hereford and Angus cows were investi- gated. Data consisted of 6977 and 6530 records of 200- (WW) and 365-d (YW) weights, respectively, of F1 calves sired by bulls (662 and 661 for WW Wand YW, respectively) of 23 breeds that have been evaluated in the Germ Plasm Evaluation Program at the U.S. Meat Animal Research Center, Clay Center, NE. Models compared included fixed effects of genetic group of sire, dam breed, sex, birth year of calf and age of dam, plus sire within genetic group and dam within dam breed as random effects. Variance structures were different: Model I assumed homogeneous variances across sire breed-sex subclasses; Model II accounted for differences in phenotypic variance by sire breed and sex subclasses. Differences between estimates of sire group effects obtained with the two models were not significant fo either WW or YW. Product-moment and rank correlations between EPDs obtain- ed with Model I and Model II were greater than 0.93 when computed within each group, and 0.99 or larger when computed across breeds. There were slight changes in the numbers of sires contributed by different breeds to the proportions selected across breeds under different selection intensities when sires were ranked with the two models. However, differ- ences between means of EPDs predicted under Model II were small when sires were ranked and selected based on EPDs obtained with the two models.