|Van vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/25/2002
Publication Date: 12/1/2002
Citation: Arango, J.A., Cundiff, L.V., Van Vleck, L.D. 2002. Genetic parameters for weight, weight adjusted for body condition score, height and body condition score in beef cows. Journal of Animal Science. 80:3112-3122. Interpretive Summary: Records of cows (n = 3,032) after 2 years of age from the first 4 cycles of the Germplasm Evaluation program at MARC were analyzed to determine genetic parameters for weight, height, and condition score. Intermediate to high estimates of heritability indicate that genetic changes in cow weight and height can be accomplished easily by selection. Measures of weight or height at different ages or seasons after 2 yrs of age can be considered t be similar genetic traits. A repeatability model would be adequate to model cow weights and cow heights. Condition score had smaller estimates of heritability and repeatability than weight and height. Condition score may be useful for evaluating cow weight at constant fatness rather than as an independent trait for selection. Results indicate no antagonistic relationships among height, weight, and condition score. Selection would be effective for either weight or height, and would produce important correlated responses for both measurements of maturity. Selection for condition score would not be as effective but would be changed by correlated response if selection is for weight. Selection for height would not be expected to affect condition score. Height is a trait that reaches a maximum earlier in life than weight and is highly correlated with weight. Measures of height at early ages might be used in multiple trait approaches to select indirectly for optimal mature weight.
Technical Abstract: Weights (CW, n= 61,798), weights adjusted for condition score (WA), heights (CH, n = 56,494) and condition scores (CS, n = 61,434) of cows (two through eight yr of age) produced by crosses of 22 sire breeds with Angus and Hereford dams in the first four cycles of the Germplasm Evaluation (GPE) Program at the U.S. Meat Animal Research Center were used to estimate genetic parameters with REML. The model included sire breed, cow line, age in years, season of measurement (1 to 4) and their interactions, year of birth and pregnancy-lactation code (PL) as fixed effects for CW and CS. Model for CH excluded PL. Random effects were additive genetic and permanent environmental effects. Univariate analyses of all data, by season and by year of age, and bivariate analyses between pairs of seasons and ages (2 to 6), and between traits were done. Estimates of heritability over all ages were 0.49, 0.54, 0.68 and 0.16 for CW, WA, CH and CS. Corresponding estimates for each age and season were similar for all trait and cycles. Estimates of genetic and permanent environmental correlations were close to unity for all pairs of seasons and traits. Genetic correlations were greater than 0.92 for all pairs of ages for CW, WA and CH, and greater than 0.67 for CS. Genetic correlations were 0.80, 0.86, 0.43 and -0.04 for CW-CH, WA-CH, CW-CS and CH-CS, respectively. Results suggest that simple repeatability models can be used to model weights and heights in this population.