Estimation of genetic parameters for growth-related traits and evaluating the results of a 27-year selection program in Baluchi sheep

Abstract

The aim of the present study was to estimate (co) variance components and genetic parameters for growth traits of Baluchi sheep as well as to study the response of Baluchi sheep to selection for yearling live weight. Data and pedigree information used in this study were collected at the Abbasabad Sheep Breeding Station from 1983 to 2011. Studied traits were birth weight (BW), 3-month weight (W3), 6-month weight (W6), 9-month weight (W9) and yearling weight (W12). Six different animal models were fitted, including or ignoring maternal effects. Estimates of breeding values were obtained by the best linear unbiased prediction (BLUP) method. Genetic trends of studied traits were estimated by regressing mean of breeding values on birth year. On the four gametic pathways, generation intervals were estimated as the average age of parents at the birth of their progeny. The estimates of direct heritability (h2) for traits studied were low and ranged between 0.03 (W6) and 0.15 (W12). Maternal genetic and environmental effects were significant on traits studied. Maternal heritability m2) was 0.09 at birth but decreased gradually and reached 0.02 at yearling age. Likewise, maternal permanent environment variance as a proportion of phenotypic variance (c2) decreased from 0.13 at birth to 0.05 at yearling age. Phenotypic correlations between various traits were positive and increased with older pairs of ages. The corresponding direct genetic correlations were all positive, with a tendency for higher estimates between pairs of older ages. Genetic changes over the experiment were −0.13kg, 0.192kg, 0.082kg, 0.147kg and 0.459kg for BW, WW, W6, W9 and W12, respectively. Annual genetic gain for BW, WW, W6, W9 and W12 were, respectively, ≈0.00g, 7g, 4g, 7g and 14g per year. The average generation interval was 3.50 years. The lower generation interval was observed on the ram side compared with the dam side (3.35 year vs. 3.81 year), indicating faster generation turnover for sires than for dams. Overall, results showed a moderate genetic improvement in growth traits of Baluchi sheep. In addition, because of significant maternal effects on growth-related traits of Baluchi sheep, to have an accurate genetic evaluation, these effects need to be considered in any breeding program aimed at improving growth traits of this breed.