Estimation of Genetic Parameters and Environmental Factors on Early Growth Traits for Lori Breed Sheep Using Single Trait Animal Model

Islamic Azad University, Karaj Branch, Iran.
Pakistan Journal of Biological Sciences 02/2008; 11(1):74-9. DOI: 10.3923/pjbs.2008.74.79
Source: PubMed


The effects of different environmental factors and estimation of genetic parameters on early growth traits for Lori breed sheep including birth weight, weaning weight and body weight at 6 months of age using 19960 records from 35 herds of Lorestan Jahad Agriculture Organization were studied in the cities of Aleshtar, Khorramabad and Poldokhtar from 1995 to 2003. The effect of herd, sex of lambs, dam age and birth year on all traits and birth type had significant effect only on weaning weight. Different single trait animal models estimated the components of direct additive genetic variance, maternal genetic variance and maternal permanent environment variance through restricted maximum likelihood using environmental factors as a fixe effect and different random effects. The results showed that direct additive genetic effect had additionally significant effect on all traits moreover maternal additive genetic and maternal permanent environment effects. Results also revealed that the maternal permanent environment variance for all traits is higher than maternal genetic variance. Also the direct heritability for all traits was higher than maternal heritability. Estimation of the direct heritability from the birth to 6 months of age showed a reducing trend that could arise from high dependence of birth and weaning weight on maternal environment conditions as compared with the age conditions afterward. The genetic assessment of growth traits in Lori breed sheep without inclusion of maternal effect in animal model causes decreased selection accuracy and incorrect genetic assessment of the lambs.

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    ABSTRACT: The aims of this study were to investigate the importance of maternal effects and to determine the most appropriate model of analyses for early growth traits of Arabi lambs. Records of 2445 lambs from 139 rams and 804 ewes for Birth Weight (BWT) on 2237 lambs from 127 rams and 784 ewes for Weaning Weight (WWT) and on 2098 lambs from 115 rams and 739 ewes for Average Daily Gain from birth to weaning (ADG) were used in this research. The data collected from Animal Science Research Station of Agricultural and Natural Resources Ramin (Khuzestan) University during 2001-2008. Genetic parameters were estimated by derivative free restricted maximum likelihood method. Six different animal models were fitted by including or excluding maternal genetic effect, maternal permanent environmental effect and covariance between direct-maternal genetic effects. On the basis of log likelihood ratio test results, Model 3 which included direct genetic and maternal genetic effects was determined to be the most appropriate model for all traits. The maternal genetic effects contributed about 74, 69 and 64% to the direct genetic effects and 15, 11 and 10% to the phenotypic variance for BWT, WWT and ADG, respectively. Depending on the model, the estimates of maternal heritability ranged from 0.074-0.146 for early growth traits of Arabi lambs. Results showed that maternal genetic effects were important for pre-weaning growth traits and should not be neglected from the model; therefore inclusion of maternal effects into the model for mentioned traits is necessary.
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    ABSTRACT: Genetic parameters and (co) variance components were estimated on 2445 lambs from 139 sires and 804 dams for Birth Weight (BW) on 2237 lambs from 127 sires and 784 dams for Weaning Weight (WW) and on 2098 lambs from 115 sires and 739 dams for Average Daily Gain (ADG). The data collected from Animal Science Research Station of Agricultural and Natural Resources Ramin (Khuzestan) University during 2001-2008. Analyses were carried out by Restricted Maximum Likelihood (REML) method. Six different animal models including or ignoring maternal genetic or permanent environmental effects were fitted for traits. The Model 3 with only maternal additive effects seemed most suitable. Influencing factors such as birth year, birth type, lamb's sex and dam's age were investigated as the fixed effects for the models. Estimates of direct heritability from model 3 were 0.194 for birth weight, 0.163 and 0.149 for weaning weight and average daily gain, respectively. Maternal hentability estimates for birth weight, weaning weights and average daily gain were 0.15, 0.11 and 0.09, respectively. For these traits, correlation estimates between direct additive and maternal genetic (r am) effects were high and negative ranging from -0.57 to 0.93. Bivariate analysis by Model 3 was also used to estimate genetic correlations between traits. The estimates of genetic, phenotypic and environmental correlations among traits were positive and intermediate to high in value. The results indicate that in addition to additive direct effect, additive maternal effect for all traits was important.
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