Genetic and phenotypic analyses of growth traits in Kordi lambs of northern Khorasan province

The objective of this study was to investigate genetic and phenotypic characteristics of body weight of Kordi lambs in different ages. Records of growth traits obtained from 5,144 lambs (progeny of 161 rams and 1,982 ewes) were used. The records of birth weight, BW (5,069 records), 3-month weight, W3 (3,968 records), 6-month weight, W6 (3,519 records), 9-month weight, W9 (2,840 records) and 12-month weight, W12 (2,595 records) and collected between 1996 and 2013 in Kordi Breeding Station in Shirvan city of northern Khorasan province. Genetic parameters were estimated applying restricted maximum likelihood method fitting an animal model using WOMBAT program. Test of significance for the fixed effects was carried out using SAS 9.2 software. The mean ± standard deviation of BW, W3, W6, W9 and W12 were 4.38±0.75, 23.47±5.77, 31.99±6.80, 35.96±7.06, and 43.23±8.44 kg, respectively. Direct heritability estimates of 0.12±0.02, 0.36±0.04, 0.31±0.03, 0.21±0.03, and 0.19±0.02 were obtained for the traits, respectively. The highest maternal heritability was estimated for BW (0.15±0.02), and then reduced as the age of lambs increased. Estimates of direct genetic and phenotypic correlations among the studied traits varied from 0.56 to 0.97 and 0.18 to 0.81, respectively. Maternal genetic correlations among growth traits ranged between 0.84 and 0.99. According to the results of this study, W3 had the highest heritability and strong genetic correlation with other traits suggesting that it could be considered as a selection criterion for growth in this breed.