برآورد برخي عوامل محيطي و ژنتيكي موثر بر وزن بدن ميش و اندازه مطلوب آن در گوسفندان

Study of factors affecting the ewe body weight and optimum ewe size in Bakhtiari shepp

In this study 3983 body weight records from 1068 ewes during 1989 to 1999 from the Station of Improvement of Bakhtiari sheep, breed were used to study of factors affecting the ewe body weight and optimum ewe size. Least-squares means (±s.e) of body weight of ewe at mating, lambing, weaning and shearing were 56.80(±0.72), 68.40(±0.16), 56.66(±0.16) and 60.(18(+_0.14) kg; respectively. Effects of mating year and age of ewe on body weights were highly significant (P<0.01). Body weights increased with increasing age of ewe, reaching a maximum at 5 to 6 years and thereafter remained fairly constant. Estimation of genetic parameters of body weight at mating were: direct heritability 0.73(±0.02), maternal heretability 0.746(+0.02), total heritability 0.459 and genetic correlation between direct and maternal additive genetic effects -0.70. Ewes ranging in body weight at mating from 55 to 65 kg had the maximum productivity. However, it could be concluded that in order to increase productivity, body weights of ewe at mating should he improved to 60±Skg. In the first step we should impove environmental [actors (e.g.maneagmcnt, nutrition,...) and then select within breed. It seems that selection within breed can make a major improvement in body weight at the time of mating but it is expected that generic progress in body weight at the time of mating may impose some restriction on selection due to negative correlation between direct and maternal values.