The estimation of (co)variance components for growth traits and Kleiber ratios in Zandi sheep

Abstract

The main objectives of present study were to estimate genetic and phenotypic parameters for economically important traits in the Zandi sheep. Traits included, birth weight (BW), weaning weight (WW), average daily gain from birth to weaning (ADG1), Kleiber ratio from birth to weaning (KR1), six month weight (6MW), average daily gain from weaning to six months of age (ADG2) and Kleiber ratio from weaning to six months of age (KR2). The data analyzed was collected from 1993 to 2008 at Khojir Breeding Station of Zandi sheep in province of Tehran, Iran. The (co)variance components were estimated fitting different animal models using a restricted maximum likelihood (REML) procedure. The most appropriate model for each trait was determined applying Akaike's information criterion (AIC). The most appropriate model for BW included direct additive genetic and maternal additive genetic effects, without taking into account covariance between them, whereas the best model for ADG1, WW and 6MW included direct additive genetic and maternal permanent environmental effects. For other traits studied (ADG2 KR1 and KR2) only direct additive genetic effects were significant random effects. Estimated direct heritability obtained from the best model were 0.15, 0.14, 0.05, 0.15, 0.02, 0.01 and 0.13 for BW, ADG1, KR1, WW, ADG2, KR2 and 6MW, respectively. The estimated of maternal heritability was 0.13 for BW. Genetic correlations among the traits studied were positive and varied from 0.14 for WW–KR2 to 0.89 for BW–6MW and ADG2–KR2. Estimates of phenotypic correlations among the traits were low to high values in magnitude and ranged from −0.23 for ADG1–KR2 to 0.88 for ADG2–KR2.