مشخصات پژوهش

In the present study, 43,441 body weight-age records (21,361 records on male lambs and 22,060 records on female lambs) on 6899 lambs descended from 235 sires and 2842 dams that collected from 1991 to 2015 in Kordi sheep breeding station, located in Shirvan city, North Khorasan province, North-eastern area of Iran, were used. Five non-linear models including Brody, Negative exponential, von Bertalanffy, Logistic and Gompertz were fitted on body weight-age data and compared applying Akaike's information criterion (AIC), mean square error (MSE) and adjusted coefficient of determination (R2 adg) for determining the most appropriate model describing the growth curve for all, male and female Kordi lambs. The Brody model showed the lowest AIC and MSE and the highest R2 adg among the tested models for all, male and female Kordi lambs. Therefore, Brody model was selected as the best one for describing growth curve in Kordi sheep. The estimated values for parameters of growth curve under Brody model including parameters A (estimated mature weight), B (an integration constant related to initial animal weight) and K (maturation rate) were 43.372, 0.905 and 0.007, respectively. Parameters of A, B and K were estimated as 48.630, 0.911 and 0.006, respectively for male lambs and 38.444, 0.898 and 0.008 for female lambs, respectively. A nultivariate animal model was considered for genetic analysis of the growth curve parameters via Gibbs sampling under a Bayesian approach with 100,000 iterations, considering the first 20,000 samples as the burn-in period and a thinning interval of 10 samples. Posterior means for heritability estimates of the studied growth curve parameters of Kordi sheep were 0.08, 0.14 and 0.04 for parameters A, B and K, respectively; showed low level of genetic variation for the parameters of growth curve in Kordi sheep. Posterior means for the estimates of genetic correlations among the studied growth curve traits were 0.48 (A-B), -0.22 (A-K) and -0.28 (B-K). The