Estimation of variance components and genetic, phenotypic and environmental trends for body weights in Kourdi sheep

The objective of the present study was to estimate genetic, phenotypic and environmental trends for body weight traits at different ages in Kourdi sheep. Thus, the records of growth traits from 5144 lambs (from 161 rams and 1982 ewes) were used. The studied traits were birth weight (5069 records), 3-month weight (3968 records), 6-month weight (3519 records), 9-month weight (2840 records) and 12-month weight (2595 records) that collected from 1996 to 2013 in Kordi Breeding Station in Shirvan city of northern Khorasan province. Variance components and genetic parameters were estimated applying restricted maximum likelihood method fitting six animal models using WOMBAT. The most appropriate model for each trait was determined based on likelihood values. Breeding values were estimated via mixed model equations by the best model for univariate analysis. Genetic, phenotypic and environmental trends were calculated by regression of means of predicted breeding values, phenotypic means and difference between estimated means of breeding values and phenotypic means on birth year for each trait, respectively. Direct heritability estimates for birth, 3, 6, 9 and 12 month weights were 0.10±0.03, 0.28±0.03, 0.32±0.04, 0.22±0.03 and 0.20±0.04, respectively. Direct genetic trends for birth, 3, 6, 9 and 12 month weights were 4.13±0.25, 117.01±5.91, 148.24±5.78, 110.01±5.83 and 122.21±6.89 g per year, respectively. The phenotypic trends for these traits were -7.47, -126.32, -490.21, -493.69 and -599.48 g per year, respectively.