Analysis of the influence of genetic and non-genetic factors on the birth weight and weaning weight of lambs

Abstract

The main aim of this paper is to analyze the influence of genetic and non-genetic factors on the birth weight and weaning weight of lambs. The study was carried out on the basis of the Institute of Animal Husbandry of Steppe Regions named by M. F. Ivanov “Askania-Nova” – the National Scientific Agricultural Center in Sheep Breeding of NAAS. Birth and weaning weights data collected during a 5-vear period from 3961 lambs were used. The reproductive traits of the Ascanian fine-fleece (AC) ewes were evaluated in combination with the rams of different genotypes: Ascanian fine-fleece, Australian merino (AM) and half-bred animals (1/2AC+1/2AM). The main effect of the ram genotype and the year of lambing, the age of the ewes, the litter size, the sex of lamb and the sex ratio in twins on the birth weight and weaning weight of lambs was analysed using one-way ANOVA. Differences between years of the 5-year period were highly significantly (P < 0.001) for all lamb traits studied. The effects of the environmental factor (year of lambing) on the birth weight and weaning weight of lambs represented 27.2 and 15.2 per cent of the total variance, respectively. The ram-group effects, which are mainly genetic differences, were highly significant (P < 0.001) in all traits. Age of dam had significant effect on the birth weight of lambs (P = 0.048) and was relatively unimportant as a source of variation. Two-year-old ewes bore lighter lambs than older ewes. There were no significant differences in the weaning weight of lambs from the ewes of different age classes. Survival rate was related to birth weight of lambs. Lamb survival increased up to a birth weight of 4.0 kg and only declined when they weighed more than 5.0 kg at birth. Our results showed that singles were 0.61 kg heavier than twins at birth and were 2.42 kg heavier than twins at weaning. Litter size (type of birth) was responsible for 42.5 and 10.0 % of total variability in birth and weaning weights of lambs, respectively (in both cases: P < 0.001). Average birth and weaning weights of male lambs were higher than the females (in both cases: P < 0.001).