آنالیز ژنتیکی صفات افزایش وزن روزانه و نسبت کلیبر در گوسفند کرمانی

Introduction[1] Kermani sheep is one of the native dual purpose breeds that adapted with Kerman province’s climate conditions. Body weight traits for sheep meat producers are very important, therefore precise evaluation of genetic factors for these traits have always been concern of breeders. Regarding to importance of meat production in economic benefit of sheep farming, this research was done with goal of genetic parameters estimation for daily gain and Kleiber ratios in Kermani sheep.
Materials and Methods This research was done by using pedigree information form 10988 Kermani sheep between 1983 to 2010 that was collected by Kermani sheep breeding station located in Shahr-e- Babak city of Kerman province, for genetic analysis of growth traits. Studied traits were average daily gain from birth to form weaning (ADG1), form weaning to 6 months (ADG2), form 6 months to 9 months (ADG3), form 9 months to 1 yearling (ADG4) and Kleiber ratios corresponding to the respective daily weight gain (KR1, KR2, KR3 and KR4). For data preparation and edition, pedigree analysis and genetic analysis of studied traits Excel, Fox Pro, CFC and Wombat Softwares were used respectively. Test of significance for the fixed effects on studied traits was done by GLM procedure of SAS 9.2 Software and significant level of p<0.05 was considered for fitting fixed effects in final model. Combined effect of HYS (23 herds), lamb sex and dam age at lambing was significant for all of studied traits. Genetic analysis of traits was performed of restricted maximum likelihood method by using of Wombat and most appropriate model according to Akaike’s information criterion was selected.
Results and Discussion In this research the records number of growth traits decreased by age due to culling of some of lambs or not registering of records in higher ages. The average daily gain of pre-weaning was calculated 231.77 gr and this trait for post-weaning periods had down trend that was complied with reported results in similar studies. Average of ADG1 in this research rather than reported amounts by other researches was more that represented high capacity of growth in Kermani lambs. The Average of ADG2, ADG3, ADG4, KR1, KR2, KR3 and KR4 were estimated 109.98, 40.78, 38.06, 19.86, 13.13, 7.63 and 3.30 gr respectively. The various climate conditions like raining content and environment temperature affects the quality and quantity of forage that resulted in significant changes at available nutrients amount of animal and supply of requirements and consequence of it the daily gain of lambs at different ages. Male lambs in all of traits compare with female lambs were more that showed that effect of sex on Kermani sheep lambs. The average of single lambs was more than twin lambs. The effect of dam age at lambing was significant on all of studied traits. The direct heritability for ADG1, ADG2, ADG3, ADG4, KR1, KR2, KR3 and KR4 were calculated 0.14, 0.15, 0.16, 0.16, 0.17, 0.19, 0.20 and 0.23 respectively. Although direct heritability of ADG1 was low, but by increasing of age the amount of direct heritability for traits increased that may be caused to the reducing effect of maternal effect on studied traits with increasing age. The total heritability for ADG1, ADG2, ADG3, ADG4, KR1, KR2, KR3 and KR4 were estimated 0.19, 0.20, 0.19, 0.16, 0.21, 0.19, 0.23 and 0.23 respectively. The covariance for ADG3 was estimated negative that shows negative presence of maternal genetic effects in this traits heritability and selection response. The genetic correlations between ADG1-KR1, ADG2-KR2, ADG3-KR3 and ADG4-KR4 were estimated 0.57, 0.74, 0.68 and 0.54 respectively. The phenotypic correlation between ADG1-KR1, ADG2-KR2, ADG3-KR3 and ADG4-KR4 were 0.84, 0.89, 0.88 and 0.98 respectively. It seems that selection for Kleiber ratio in each period resulted in increasing daily gain at that period too. Therefore, by selection according to Kleiber ratio, the average of food efficiency will increase. Between environmental correlation of studied traits with direct correlation of them showed that the difference among them was low in most of cases. Thus, regarding to available information it seems that the univariate model was more appropriate in genetic evaluation of studied traits.
Conclusion The results of this research showed that selection according to Kleiber ratio in Kermani sheep can increase the efficiency of feed intake. More than this, the Kleiber ratio has this advantage that at calculating, starter and finisher weights of period which estimation of them are simple.