Estimation of (co)variance components and genetic parameters for the growth curve characteristics of Iranian Moghani sheep

Background and Aim: The aim of this study was to estimate (co)variance components and genetic parameters of the growth curve parameters of Iranian Moghani sheep.Methods: In this study, the data related to the birth weight, weaning weight, ۶-month weight, ۹-month weight and yearling weight of ۱۰۷۲۴ Moghani sheep collected at the Moghani sheep breeding station in Jafarabad, Moghan, during the years ۱۹۸۹ – ۲۰۱۶ were used to investigate the growth curve of this breed. Five nonlinear models including Brody, Logistic, Gompertz, Von Bertalanffy, and negative exponential models were used to describe the growth curve of Moghani sheep. Growth curve parameters including A (asymptotic mature weight), B (initial animal weight) and K (maturation rate) were estimated for each individual animal using the Logistic model as the best fitted model according to the coefficient of determination (R۲) and Akaike information criterion (AIC). Significant environmental factors affecting the parameters of the growth curve were determined using analysis of variance. These effects were then used in six animal models to estimate the heritability of growth curve parameters. These models were different in terms of random genetic effects, permanent environmental effect, and maternal genetic effect.Results: Fixed effects of lamb sex, birth type, year and month of birth and age of dam at birth had significant effect on growth curve parameters. Direct heritability for asymptotic mature weight (A), initial animal weight (B) and maturation rate (K) were equal to ۰.۱۷۱, ۰.۰۷۹ and ۰.۲۵۰, respectively. Covariance between direct genetic effect and maternal genetic effect for asymptotic mature weight and maturation rate were -۵.۲۴ and -۰.۴۹, respectively. Correlation coefficients between A-B, A-K, and B-K were ۰.۳۴, -۰.۲۶ and -۰.۱۲, respectively. Positive correlation between A-B indicated that heavy lambs at birth had greater mature weight. The negative correlation between A and K suggests that animals maturing fastest have a lower weight at maturity than slowly maturing animals.Conclusion: According to the results of this study, the growth curve parameters of this breed had an acceptable heritability so that these traits could be used in breeding programs to change the growth curve of this breed and improve the weight of animals in this breed.

کلیدواژه ها:

Heritability ، Growth curve ، Logistic Model ، Moghani Sheep