Adjustment factors and genetic parameter estimates for yearling pelvic area in Limousin cattle

Abstract

Data on 2,704 bulls and 11,049 heifers provided by the North American Limousin Foundation were analyzed separately to determine age and age of dam adjustment factors for yearling pelvic area and to estimate heritabilities and genetic correlations for yearling pelvic area and other performance measures. An animal model and derivativefree REML incorporating sparse matrix techniques were used. Regression coefficients for pelvic area on age were .29 and .3 5 CM2 /day for bulls and heifers, respectively, between the ages of 320 and 450 days. Age of dam adjustment factors were 8.58, 3.30 and 3.30 CM2 for bulls born to 2, 3 and 4 year old dams, and 4.92 and 2.31 cM2 fo r heifers produced by dams aged 2 and 3, respectively. Heritability estimates for pelvic area were .26 for bulls and .30 for heifers indicating that pelvic area can be modified through selection. Genetic correlations between pelvic area and birth weight direct, weaning weight direct, yearling weight and yearling hip height converged at . 16, .3 9, .65, and l.00 for bull sand .ll, .16,.52, and .72 for heifers, respectively. Althoughhigh genetic associations were found between pelvic area and measures of yearling growth, when yearling weight was introduced into the pelvic area model as an additional covariate, heritabilities were nearly as high as age adjusted estimates (. 21 and .26 for bulls and heifers, respectively), indicating that a considerable amount of additive genetic variance exists that is not accounted for by body weight. The genetic correlation between pelvic area and yearling scrotal circumference was favorable (.39). When bull and heifer data were combined in the form of a bivariate animal model, the genetic correlation between male and female pelvic area was .83. This suggests that male and female pelvic area are largely under the same genetic control and that selection of sires with large pelvic openings should result in increased pelvic area in their female offspring. Heritability estimates for pelvic area converged at .31 for both bulls and heifers when the data were combined in the bivariate animal model.