estimation of genetic, phenotypic and environmental trends of growth traits in kermani sheep

in this study the data of 2332 lambs from 815 dams and 61 sires, collected during 1993-2004 in kermani sheep breeding station were used to estimate phenotypic, genetic and environmental trends for birth weight (bw), weaning weight (ww), 6 months weight (6mw), 9 months weight (9mw) and yearling weight (yw). heritability estimates were determined for each trait using derivative free reml procedures under univariate animal model. by excluding or including maternal genetic effects or maternal permanent environmental effects, six different models were fitted for each trait. likelihood ratio test was used to determine the appropriate model. this test indicated that the model including direct and maternal genetic effects, without covariance between them, was the appropriate model for bw. the model including direct genetic effects and maternal permanent environmental effects was the most appropriate model for ww, 6mw and 9mw. the model including direct genetic effects was the most appropriate model for yw. phenotypic, genetic and environmental correlations were estimated under multivariate analysis using the most appropriate model for each trait. breeding values were estimated under univarite and multivariate analyses. genetic, phenotypic and environmental trends were estimated by regression of the estimated mean of breeding values, phenotypic mean and difference between estimated mean of breeding values and phenotypic mean on birth year, respectively. the average additive direct genetic trends for bw, ww, 6mw, 9mw, yw in univariate and multivariate analyses were 0.53±0.30 and 0.84±1.14, 96.41±18.27 and 101.29±37.41, 88.24±26.11 and 90.51±48.34, 24.35±10.68 and 29.76±11.49 and 31.53±10.43 and 35.18±12.58 gr per year, respectively. the estimates of maternal additive genetic trend for bw in univariate and multivariate analyses were 3.07±1.21 and 2.91±1.67 gr per year, respectively.