Genetic and non-genetic factors affecting Lori-Bakhtiari ewe body weight and its relationship with productivity

Abstract

The data set used in this study consisted of 22,493 records of ewe body weight, measured a maximum of four times per year on 1935 ewes, collected from 1989 to 2007 inclusive from a Lori-Bakhtiari research flock at Shooli station in Shahrekord. Genetic and non-genetic parameters were estimated using restricted maximum likelihood and GLM procedure in multi-trait animal model. The model included the fixed effects age of ewe, stage of production and year of recording, and random effects direct additive genetic, permanent environmental and residual. The animal model was employed to identify the effect of ewe body weight (as classification and continuous variable) on ewes productivity traits. The age of ewe, stage and year of production had significant ( p < 0.01) effect on ewe body weight. The least squares means of ewe body weight ranged from 55.78 to 65.01 kg, increasing with age of ewe, the maximum body weight observed in 5 years old group and then decreased in the older age groups. The lowest ewe weight was seen at mating. The maximum ewe weight observed after parturition and decreased after weaning and at shearing. The heritability estimates of ewe weight at different stages of production as various traits were high (0.40–0.49). The estimates of genetic correlation between ewe weights at different stages of production were high and ranged from 0.89 to 0.99. Ewe body weight at mating affected all traits related to ewe's productivity significantly ( p < 0.05 or 0.01). There was a rising pattern in conception and lambing rate as weight of ewe increased up to overall mean plus 5 kg (56.59–61.58 kg) and a decline thereafter. The least squares means of number of lambs born and weaned, total litter weight (kg) at birth and weaning per ewe exposed increased with increasing ewe weight at mating. The total litter weight (g) at birth and weaning per kg body weight of ewe exposed decreased with increasing ewe weight at mating. The least squares means of total litter weight (g) at birth and weaning per kg metabolic body weight of ewe (BWT 0.75) exposed increased with ewe weight up to overall mean plus 5 kg and then declined. Thus, the highest productivity was for ewes ranging in weight from mean plus and minus 5 kg at mating in Lori-Bakhtiari ewes (56.58 ± 5 kg).