Genetic, Phenotypic and Environmental Trends for Growth and Reproductive Traits in Zandi Sheep

Abstract

This paper reports the genetic, phenotypic and environmental trends for growth traits including birth weight (BW), weaning weight (WW), 6-month weight (6MW), 9-month weight (9MW) and yearling weight (YW). Reproductive traits namely, litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) were also investigated. The data were collected from the Khojir Breeding Station of Zandi sheep in Tehran, Iran from 1993 to 2008. Best linear unbiased prediction (BLUP) of breeding values was estimated by Restricted Maximum Likelihood procedure using multi-trait animal model. The most appropriate models were chose to predict breeding values of aforementioned traits. Genetic and phenotypic trends were obtained by regression of average breeding values and phenotypic least squares mean, respectively, on birth year. Direct genetic trends were significant for BW, WW, 6MW, 9MW, YW, TLWB and TLWW (5, 48, 21.5, 72, 65, −2.5 and 11 g per year, respectively). Phenotypic ones were significant for WW, 6MW, and TLWW (129.5, 238.3, and 187.3 g per year respectively). Environmental ones were significant for WW and 6MW (81.5, and 216.8 g per year, respectively). Both LSB phenotypic and environmental trends were −0.010 head per year. The results showed that Selection program would relatively bring out genetic improvement especially for growth traits in mentioned breed. Environmental fluctuations ought to be modified with particular managing schedules to provide a susceptible field to express genes’ additive effects.