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

The purpose of this study was to investigate the genetic, phenotypic and environmental trends of growth traits in Shal sheep. In this regard, records were collected on the growth traits of 6692 lambs that were collected from 1997 to 2013 at Shal Sheep breeding station located in Qazvin province. The studied traits included birth weight (6690 records), three months weight (6654 records), six month weight (6662 records), nine months weight (6599 records) and twelve months weight (6528 records). Genetic parameters were estimated using WOMBAT software with limited likelihood method. The genetic, phenotypic and environmental trends of the traits were estimated using the regression coefficient of average breeding values, phenotypic and environmental on birth year, respectively. Direct heritability of body weight at different ages based on the most suitable model for birth weight, three, six, nine, and twelve months were 0.13±0.02, 0.57±0.05, 0.52±0.05, 0.79±0.04, and 0.73±0.05 respectively. Correlation between direct and maternal incremental genetics in all negative traits was obtained. The genetic trend for the traits was -0.86, -10.19, -27.45, -15.73 and -2.44 g/y, respectively. The phenotypic trend was 12.84, -65.19, -57.35, -53.92 and -57.59 g/y, respectively, and also the environmental trends were estimated and environmental trends were 4.33, -21.56, -26.47, -0.98 and -41.91 g/y, respectively. Genetic, phenotypic and environmental trends of all traits were not significant. The results of this study indicate that there is no positive genetic growth of Shal sheep weight traits in recent years. Therefore, appropriate breeding programs are recommended for genetic improvement of the mentioned traits in shal sheep.