Parameter estimates for greasy fleece weight of Rambouillet sheep at different ages

Variance components for greasy fleece weight in Rambouillet sheep were esti mated. Greasy fleece weight was modeled either as repeated measurements on the same trait or as different traits at different ages. The original data were separated according to the age of the ewe at shearing into three class es; 1 yr, 2 and 3 yr, and older than 3 yr. An animal model was used to obta in estimates of genetic parameters with a REML algorithm. Total numbers of animals in pedigrees for the different age classes were 696, 729, and 573, respectively, and 822 for the repeated measures model across ages. The anim al model included direct genetic, permanent environmental, and residual env ironmental random effects and fixed effects for age of ewe, shearing date a s contemporary group, and number of lambs born. Days between shearings was used as a covariate. Single-trait analyses were initially done to obtain st arting values for multiple-trait analyses. A repeated measures model across ages was also used. Estimates of heritability by age group were .42, .50, and .58 from three-trait (age class) analyses and for the repeated measures model the estimate was .57. Estimates of genetic correlations between flee ce yields for 1 yr and 2 and 3 yr, 1 yr and >3 yr, and 2 and 3 yr and >3 yr classes were .88, .89, and .97, respectively. These estimates of genetic c orrelations suggest that a repeated measures model for greasy fleece weight is adequate for making selection decisions.