بررسي صحت ارزش اصلاحي پيش‏بيني شده در مرغان بومي خراسان براي صفت وزن بدن در سن هشت هفتگي

Astudy on accuracy of predicted breeding value for body weight at eighth week of age in Khorasan native chickens

در هر برنامه اصلاح‏نژادی هدف آن است كه ارزش اصلاحی حیوانات، با دقت و صحت بالایی پیش‏بینی گردد تا بر اساس آن بتوان بهبود ژنتیكی قابل ملاحظه‏ای را در طول زمان برای صفات مورد نظر، ایجاد نمود. هدف از این تحقیق، بررسی صحت ارزش اصلاحی پیش‏بینی شده در مرغان بومی خراسان برای صفت وزن بدن در سن هشت هفتگی بود. داده‏های مورد استفاده، تعداد 47000 ركورد وزن بدن متعلق به 47000 جوجه (نتاج 753 خروس و 5154 مرغ)، جمع‏آوری شده طی هفت نسل (1391-1385) بود. مدل آماری مورد استفاده برای آنالیز داده‏ها، یك مدل حیوانی بود، كه در آن گروه همزمان نسل - هچ - جنس، متغیر كمكی وزن جوجه در سن یك روزگی، و اثرات تصادفی ژنتیكی افزایشی مستقیم و مادری گنجانده شدند. مدل مزبور بر داده‏ها توسط نرم‏افزار DMU برازش داده شد. وراثت‏پذیری مستقیم و مادری صفت وزن بدن در سن هشت هفتگی به ترتیب 4387/0 و 0483/0 برآورد گردید. میانگین ارزش اصلاحی مستقیم و مادری به ترتیب 65/76 و 91/7- گرم و میانگین صحت ارزیابی ژنتیكی (مستقیم و مادری) به ترتیب 741/0 و 427/0 بود. برآورد روند ژنتیكی برای صفت وزن بدن در هفته هشتم و بر اساس ارزش اصلاحی مستقیم و مادری به ترتیب 344/1 ± 951/26 گرم و 199/0± 252/2- گرم به¬دست آمد. روندهای مزبور به¬لحاظ آماری معنی‏دار بودند. از آن‏جا كه صحت انتخاب یكی از اجزای مهم اثرگذار بر میزان پیشرفت ژنتیكی صفات محسوب می‏گردد، لذا بر اساس نتایج تحقیق حاضر، نتیجه‏گیری می‏شود كه در رابطه با صفت وزن بدن در سن هشت هفتگی مرغان بومی خراسان، انتخاب ژنتیكی، با صحت نسبتاً بالایی اجرا گردیده است.

Introduction: Genetic resources in any country are valuable materials which needed to be conserved for a sustainable agriculture. An animal phenotype is generally affected by genetic and environmental factors. To increase mean performance in a population under consideration not only environmental conditions, but also genetic potential of the animals should be improved. Although, environmental improvement could increase the level of animals’ production in a more rapid way, it is not a permanent and non-cumulative progress. In any breeding schemes prediction breeding value of the candidate animals is needed to be obtained with a high precision and accuracy for making a remarkable genetic gain for the traits over the time. The main objective of the present research was to study accuracy of predicted breeding value for body weight at eighth week of age in indigenous chickens of Khorasan Razavi province. Materials and methods: A set of 47,000 body weight (at the age of eight weeks) records belonging to 47,000 head of male and female chicks (progeny of 753 sires and 5,154 dams) collected during seven generations (2006-2012) was used. The data were obtained in Khorasan Razavi native chicken breeding center. An animal model was applied for analyzing the records. In the model, contemporary group of generation*hatch*sex (GHS) as a fixed effect, weight at birth as a covariable, as well as direct and maternal additive genetic random effects were taken into account. In an initial analysis using SAS software, all fixed and covariate factors included in the model were detected to be significant for the trait. All additive genetic relationships among the animals in the pedigree file (47,880 animals) were accounted for. Variance and covariance components of direct and maternal additive genetic effects were estimated through restricted maximum likelihood (REML) method. Breeding value of the animals was obtained by best linear unbiased prediction (BLUP). Selection accuracy was then calculated based on prediction error variance (PEV). The model was fitted to the data using DMU package. Post analysis of breeding values (genetic trend estimation and statistical comparison of groups using student’s t test) was also undertaken using SPSS software. Results and Discussion: Average and standard deviation of body weight at the age of eight weeks were 607.93 g. and 127.347 g., respectively. As expected, males (668.98 g.) were generally heavier than females (549.86 g.) chickens. Additive and maternal genetic variance components were 3183.9253 and 350.8929, respectively. Based on genetic covariance (-363.8555) the correlation between direct and maternal genetic effects was revealed to be -0.3442. Direct and maternal heritability for the trait were found to be 0.4387 and 0.0483, respectively. Mean direct and maternal breeding values were 76.65 g. and -7.91 g., respectively. The corresponding figures for the direct and maternal accuracies were 0.741 and 0.427, respectively. Genetic trends for direct and maternal breeding value were 26.951 g. (SE=1.344 g.) and -2.252 g. (SE=0.199 g.), respectively and statistically significant (P <0.0001). For the sires, mean direct breeding value (90.77 g.) was greater than the mean maternal breeding value (-9.18 g.) and the same pattern was also found for mean selection accuracy (0.89 vs. 0.61). For the sires, a high positive and significant Pearson correlation was obtained between the number of progeny and selection accuracy for direct (0.885) and maternal (0.683) breeding values. However, both direct (-0.071) and maternal (0.052) breeding values had non-significant correlation with the number of progeny. A high significant positive correlation was also found between direct and maternal selection accuracies (0.724). Conclusion: The findings of the current research indicate that body weight at eighth week of age in indigenous chickens of Khorasan Razavi province has genetically been evaluated with a rather high degree and acceptable precision. High estimate of direct heritability of the trait indicates that there is a substantial genetic potential in the population to be improved over the generations. Moreover, the results also suggest that the number of progeny is an important factor for increasing selection accuracy.