Comparison various animal models for estimation of (Co) variance components and genetic parameters for growth traits in Zandi Sheeps

In this study (Co) variance components and genetic parameters for growth traits in Zandi Sheeps estimated by various animal models. The data used in this study, related to birth weight, weaning weight, 6 month weight, 9 month weight and yearling weight. The data collected during 1991-2011 by Nakhjir station in Tehran. (Co) variance components and genetic parameters were estimated by restricted maximum likelihood (REML). Environmental factors such as birth season, birth year, sex of lamb, birth type and mother's age at birth were significant on all traits and were fixed effects in model. The fit model by lowest AIC for birth weight, weaning weight, 6 month weight, 9 month weight and yearling weight selected 6, 2, 6, 4 and 4, respectively. Direct heritability was estimated for these traits results fitted models, 0.13±0.03, 0.17±0.03, 0.17±0.04, 0.07±0.03 and 0.18±0.06, respectively. Maternal heritability for birth weight, 6 month weight, 9 month weight and yearling weight were estimated 0.09±0.02, 0.04 ±0.02, 0.03±0.02 and 0.05±0.02, respectively. The selected models for these traits showed that maternal genetic effects, have important role in the occurrence of these traits. Estimated low heritability for these traits indicating that genetic improvement was slow for these traits and will be mostly affected by the herd management.