Authors
1
Department of Animal Science, Faculty of Animal and Aquatic Science, Sari Agricultural Sciences and Natural Resources University, Sari, Iran
2
Sari Agricultural Sciences and Natural Resources University
3
Dep. of Animal Science, Faculty of Animal and Aquatic Science, Sari Agricultural Sciences and Natural Resources University, Sari, Iran
Abstract
Back ground and objectives: Reproductive traits in sheep play an important role in improving flock productivity and economic efficiency and directly affect lambing rate, fertility and lamb survival. The study and separation of maternal effects (genetic and permanent environmental), direct additive autosomal and sex-linked genetic effects play a significant role in breeding programs and more accurate estimation of (co)variance components. The present study aimed to investigate the additive genetic effects related to the sex chromosome on the genetic parameters of ewe reproductive traits, including the litter mean weight per lamb born (LMWLB), the litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) in Baluchi sheep.
Materials and methods: Phenotype and pedigree data used in this study, related to the first calving, were collected at the Baluchi Sheep Breeding station of Abbasabad, Mashhad. The pedigree was checked using CFC software and possible errors were identified and fixed. The GLM procedure in SAS statistical software was used to identify significant fixed effects to be included in the final animal models. Year of lambing and number of lambs per lambing were included as non-genetic factors in linear animal models. Twelve univariate animal models were analyzed using WOMBAT software under the restricted maximum likelihood procedure to identify direct additive autosomal genetic effects, sex-linked additive genetic effects and, maternal effects (genetic effects and permanent environmental effects). Akaike information criterion was used to compare the models and identify the best model.
Results: Based on AIC values, the model that included additive direct genetic effects, maternal effects, covariance between direct genetic and maternal effects, and sex-linked additive genetic effects was identified as the best model. Direct heritability (h_a^2) for TLWB, LMWLB, TLWW and LMWLW was equal to 0.07±0.01, 0.08±0.02, 0.10±0.02 and 0.08±0.03. Sex-linked Heritability estimates (h_s^2) for these traits were 0.05±001, 0.06±0.01, 0.05±0.01 and 0.05±0.01, respectively. Maternal heritabilities (h_m^2) were lower than direct heritabilities for the studied traits and were estimated as 0.04±0.01, 0.06±0.02, 0.03±0.01 and 0.03±0.02. The ratio of variance caused by maternal permanent environmental effects to phenotypic variance for the studied traits was lower than direct heritabilities. Genetic covariances between direct and maternal genetic effects for all traits were positive and ranged from 0.85 to 0.93.
Conclusions: The findings of this research showed the importance of considering maternal effects (genetic and permanent environmental) and sex-related additive genetic effects in the genetic evaluation of reproductive traits in Baluchi sheep. Considering the significant sex-linked direct additive genetic effects, ignoring these effects can lead to a decrease in the accuracy of the genetic evaluations.
Keywords
Main Subjects
)