Estimation of genetic parameters and genetic trend of litter size in under selection flock of Afshari sheep

In this study, data from 1882 ewes, including 3351 lambs born, was used as litter size trait in Afshari sheep breed. The data were collected from 2000 to 2016 by the research station at Zanjan University. The data were analyzed by ASReml software via threshold model in six different models. Fixed effects of year and season, age of ewe, number of parturition and genetic group [at five levels including pure Afshari, 50% Afshari (F1), 75% Afshari (B1), 87.5% Afshari (B2) and 93.75% Afshari (B3)] were significant (P<0.05). Heritability and repeatability were estimated to be as 0.08 and 0.17, respectively. Genetic trends of this trait, in two periods between 2000 to 2006, before the gene introgression design as first period, and from 2007 to 2016, after the introgression as second period, were 0.004 (P>0.05) and 0.059 (P<0.05), respectively. Also, the phenotypic trends were 1.37 (P>0.05) and 1.69 (P<0.05) for two periods, respectively. The results showed that the FecB gene transfer increased the litter size. Consequently, because of the direct relationship between the more profitability of flock and the increase in the number of lambs born, the gene transfer design will be followed and more welcomed by sheep breeders. Therefore, genetic parameters and genetic trends estimation of litter size in this flock can be effective for developing continues genetic breeding strategy.