|Rumph, Janice - UNIV. OF NEBRASKA|
|Koch, Robert - RETIRED,UNIV. OF NEBRASKA|
|Gregory, Keith - ARS COLLABORATOR|
|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 2001
Publication Date: March 1, 2002
Citation: Rumph, J.M., Koch, R.M., Gregory, K.E., Cundiff, L.V., Van Vleck, L.D. 2002. Comparisons of models for estimation of genetic parameters for mature weight of Hereford cattle. Journal of Animal Science. 80:583-590. Interpretive Summary: Mature cow weight (MW) affects many aspects of production, including maintenance requirements, reproduction and cull cow value, and therefore profitability of the cow-calf operation. Because of these impacts on economics of production, MW should be considered in selection programs. For selection to be effective, good estimates of genetic parameters associated with MW must be available. Previous estimates of direct heritability have been variable, but generally have been moderate to high using various models. Although several methods and models have been used to estimate components of variance for MW, maternal effects typically have not been included in models for MW. In this study of Hereford cattle, estimates of direct heritability for mature weight were high. Maternal effects, previously not considered to be important, were statistically significant in this population of Hereford cattle. This result suggests the appropriate emodel for genetic evaluation for MW should consider maternal genetic effects and maternal permanent environmental effects of the dam as well as direct genetic effects of the cow and permanent environmental effects of the cow.
Technical Abstract: Genetic parameters of mature weight (MW) are needed for effective selection and genetic evaluation. Data were collected from 1963-1985 and consisted of 32,018 MW records of 4,175 Hereford cows that were in one control and three selection lines. Several models and subsets of the data were considered. The MW records consisted of a maximum of three seasonal weights taken each year, at brand clipping (February and March), before breeding (May and June), and at palpation (August and September). Heritability estimates were high (.49 to .86) for all models considered. The best model included maternal genetic and permanent environmental effects in addition to direct genetic and permanent environmental effects. Estimates of direct heritability ranged from .53 to .79, estimates of maternal heritability ranged from .09 to .21, and estimates of genetic correlation between direct and maternal effects ranged from -.16 to -.67 for subsets of data based on time of year measured. For those subsets, estimates of proportions of variance due to direct permanent environment and maternal permanent environment ranged from .00 to .09 and .00 to .06, respectively. Using the same model, but combining all records and including an added fixed effect of season of measurement, estimates of direct heritability, maternal heritability, genetic correlation between direct and maternal effects, proportion of variance due to direct permanent environmental effects, and proportion of variance due to maternal permanent environmental effects were .69, .13, -.65, .00, and .04, respectively.