Estimation of genetic, phenotypic and environmental trends for growth traits in Mehraban sheep

Estimation of genetic, environmental and phenotypic trends in past age is taken to measure the past animal breeding and management programs and design of programs for the hereafter. In the present study, in overall, 28782 records of growth traits of Mehraban sheep, collected by the Deputy of Livestock Affairs, Agricultural Jihad of Hamedan province during 1994 – 2010, were used to estimate genetic, phenotypic and environmental trends for body weight traits of Mehraban sheep. Variance components and breeding values for different traits were estimated using univariate and multivariate analyses of animal models by Average Information algorithm of Restricted Maximum Likelihood (AI-REML). Genetic, phenotypic and environmental trends were estimated based on the regression coefficient of average breeding values on birth year and regression coefficients of average phenotypic values and environmental deviations on weighting year, respectively. Estimates of genetic trends for birth weight, weaning weight and the weights at 6, 9 and 12 months of age were -1.59, -16.87, -3.27, -16.8 and -3.48 gr/yr, using univariate analyses and -1.33, -25.63, -11.34, -35.6 and -9.06 gr/yr, using multivariate analysis, respectively. Estimates of phenotypic trends were -46.31, 149.64, 475.16, 716.75 and 1050.6 gr/yr, using univariate analyses and -5.63, 109.33, 482.05, 816.68 and 1077.73 gr/yr, using multivariate analysis and estimates of environmental effects trends were -44.82, 156.7, 483.43, 732.75 and 1054.08 gr/yr, using univariate analyses and 1.44, 125.36, 491.21, 852.93 and 1086.8 gr/yr, using multivariate analysis, respectively. Only genetic trends of birth and weaning body weights and phenotypic trend of birth weight in multivariate analysis and also genetic, phenotypic and environmental parameters of birth weight and phenotypic and environmental parameters of body weights at 6 and 12 months of age in univariate analyses were significant. The outcomes of the present study indicated negative genetic trends for birth and weaning body weights and generally, absence of positive genetic improvement of body weight traits in Mehraban sheep during past years and a need to design animal breeding programs for genetic improvement of the mentioned traits in Mehraban sheep.