Genetic parameter estimates for growth and reproductive traits in Lori sheep

Abstract

Lori sheep is one of the well adapted and relatively heavy breeds in mountainous regions of Iran, primarily reared for mutton production. The current study was conducted to estimate the (co) variance components and genetic parameters by restricted maximum likelihood method using six univariate models for growth and four univariate models for reproductive traits. Data and pedigree information were collected at Agricultural Organization of Lorestan province, west of Iran from 2001 to 2012. Studied growth traits were birth weight (BW), weaning weight (WW), 6-month weight (6MW), average daily gain from birth to weaning (ADG0–3), average daily gain from birth to 6-month (ADG0–6), average daily gain from weaning to 6-month (ADG3–6), and corresponding Kleiber ratio (KR0–3, KR0–6, KR3–6). Reproductive traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lambing (LMWL), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Moreover, multivariate analyses were performed to estimate covariance between traits. Direct heritability estimates (h2a) for growth traits ranged from 0.000 (ADG0–3 and KR0–3) to 0.156 (6MW). Maternal heritability (h2m) decreased from 0.110 at birth to 0.022 at 6-month weight. The ratio of maternal permanent environmental variance to phenotypic variance (pe2) persisted into the post-weaning growth period and it was 0.115, 0.080, 0.087 and 0.081, for BW, ADG0–6, KR0–3 and KR0–6, respectively. Estimates of h2a for reproductive traits were significant for LSB, LSW, LMWL and LMWLW being 0.175, 0.213, 0.088 and 0.034, respectively, while TLWB and TLWW were more affected by the permanent environmental effects of ewes. Service sire effects (S2) were significant for LMWL. Genetic correlations between growth traits ranged from −0.425 (BW-KR0–3) to 1.000 (6MW-ADG0–3, 6MW-KR0–3, ADG0–3–ADG3–ADG3–6-KR0–3 and KR0–3–KR0–6), and phenotypic correlations ranged from −0.341 (ADG0–3–KR3−6) to 0.990 (6MW–ADG0−6). Genetic correlations between reproductive traits were higher than phenotypic ones, and ranged from −0.986 (LSB-LMWLW) to 0.999 (LMWLW-TLWB).