Genetic parameters for growth traits for a composite terminal sire breed of sheep

Records of 9,055 lambs from a composite population originating from crossin g Columbia rams to Hampshire x Suffolk ewes at the U.S. Meat Animal Researc h Center were used to estimate genetic parameters among growth traits. Trai ts analyzed were weights at birth (BWT), weaning (7 wk, WWT), 19 mo (W19), and 31 mo (W31) and postweaning ADG from 9 to 18 or 19 wk of age. The ADG w as also divided into daily gain of males (DGM) and daily gain of females (D GF). These two traits were analyzed with W19 and with W31 in three-trait an alyses. (Co)variance components were estimated with REML for an animal mode l that included fixed effects of sex, age of dam, type of birth or rearing, and contemporary group. Random effects were direct and maternal genetic of animal and dam with genetic covariance, maternal permanent environmental, and random residual. Estimates of direct heritability were .09, .09, .35, . 44, .19, .16, and .23 for BWT, WWT, W19, W31, ADG, DGM, and DGF, respective ly. Estimates of maternal permanent environmental variance as a proportion of phenotypic variance were .09, .12, .03, .03, .03, .06, and .02, respecti vely. Estimates of maternal heritability were .17 and .09 for BWT and WWT a nd .01 to .03 for other traits. Estimates of genetic correlations were larg e among W19, W31, and ADG (.69 to .97), small between BWT and W31 or ADG, a nd moderate for other pairs of traits (.32 to .45). The estimate of genetic correlation between DGM and DGF was .94, and the correlation between mater nal permanent environmental effects for these traits was .56. For the three -trait analyses, the genetic correlations of DGM and DGF with W19 were .69 and .82 and with W31 were .67 and .67, respectively. Results show that mode ls for genetic evaluation for BWT and WWT should include maternal genetic e ffects. Estimates of genetic correlations show that selection for ADG in ei ther sex can be from records of either sex (DGM or DGF) and that selection for daily gain will result in increases in mature weight but that BWT is no t correlated with weight at 31 mo.