مطالعه ساختار شجره و اثرات ناشي از افت همخوني بر صفات رشد در گوسفندان بومي استان لرستان

Study of pedigree structure and effects of inbreeding depression on growth traits in Lorestan native sheep

هدف از مطالعه حاضر بررسی شجره و افت همخونی بر صفات رشد در گوسفند لری می¬باشد. برای انجام پژوهش حاضر از اطلاعات شجره و ركوردهای مرتبط با صفات رشد شامل وزن‌ تولد، وزن‌شیرگیری، وزن شش‌ماهگی و وزن‌نه‌ماهگی 6440 رأس بره حاصل از 273 رأس قوچ و 1955 رأس میش كه طی سال‌های 1380 تا 1389 از مركز تحقیقات كشاورزی و منابع طبیعی استان لرستان جمع‌آوری شده بود، استفاده گردید. تجزیه شجره از برنامه Pedigree ، برآورد ضریب‌همخونی از برنامه CFC و برای محاسبه میزان تابعیت صفات از همخونی، از نرم افزار WOMBAT استفاده گردید. در كل جمعیت تعداد حیوانات همخون 2126 دام بودند كه 33 درصد گله را شامل می‌شد. میانگین ضریب‌همخونی كل جمعیت 69/0 درصد و میانگین ضریب ‌همخونی جمعیت همخون 24/2 درصد برآورد گردید. روند تغییرات سالیانه ضریب ‌همخونی 21/0 درصد بود كه به لحاظ آماری معنی‌دار می‌باشد. كمترین و بیشترین مقدار همخونی به ترتیب صفر و 85/26 درصد محاسبه شد. پایین بودن ضریب‌همخونی گله می‌تواند ناشی از نامعلوم بودن شجره برخی حیوانات، نوسانات مدیریتی و تا حدی ممانعت از آمیزش‌ خویشاوندان نزدیك باشد. اثر همخونی در جمعیت گوسفندان لری با استفاده از مدل‌های حیوانی مناسب برای هر صفت تولیدی بررسی شد. با افزایش هر یك درصد افزایش در همخونی، وزن‌تولد 4 گرم، وزن‌شیرگیری 3/20 گرم، شش ‌ماهگی 247 گرم و نه‌ماهگی 5/4 گرم كاهش پیدا كرده است. استفاده از یك برنامه آمیزش مستقیم تحت كنترل در گله حاضر می‌تواند جایگزینی مناسب برای حفظ سطح همخونی شود.

Inroduction: Inbreeding is defined as the probability that two alleles at any locus are identical by descent and occur when related individuals are mated to each other. The initial consequence of inbreeding is inbreeding depression reducing the performance of growth, production, health, fertility, and survival traits. This concern has become more serious in animal breeding nowadays, in which selection responses are maximized using animal model best linear unbiased predictors (BLUP) of breeding value. The use of these breeding values alone may result in more closely related selection candidates preferred for selection, with increased levels of inbreeding since they share most of their familial information. The unavoidable mating of related animals in closed populations leads to accumulation of inbreeding and decreased genetic diversity. Inbreeding has deleterious effect on additive genetic variance as well as on phenotypic values. Heterozygosity and allelic diversities can be lost from small, closed, selected populations at a rapid rate. The rates of inbreeding must be limited to maintain diversity at an acceptable level so that genetic variation will ensure that future animals can respond to changes in environment. Inbreeding depression has been found in a large proportion of species examined. Lori sheep breed is mainly raised in Lorestan Province in Iran. This study was conducted to identify pedigrees and inbreeding depression on growth traits in Lori sheep population from 2001 to 2010. The rate of inbreeding needs to be limited to maintain diversity at an acceptable level so that genetic variation will ensure that future animals can respond to changes in the environment and to selection. Without genetic variation, animals cannot adapt to these changes. Material and Methods: For this study pedigree information and body weight at different ages (birth weight, weaning weight, 6-month weight, and 9-month weight) of 6440 lambs from 273 rams and 1955 ewes during the years 2001 to 2010 from Lorestan Agricultural and Natural Resources Research Center were used. The pedigree corrections were done by the Excel program and the estimation of inbreeding coefficients was done by pedigree software. To study the pedigree, Pedigree, program, or estimate inbreeding coefficient, CFC program, and for calculate the amount of inbreeding citizenship traits, wombat software were used. Results and Discussion: In total population the number of inbred animals were 2126 (33%) of the herd. The average total population inbreeding coefficient and average inbreeding coefficient inbred of population were 0.69% and 2.24%, respectively. Annual changes in inbreeding coefficient was 0.21, which was statistically significant (p <0.0001). The maximum and minimum amounts of inbreeding were 26.85% and 0% respectively. In this pedigree, low amount of inbreeding coefficient was owing to some unknown pedigree of animals, management changes, and partially inhibit intercourse near relationship. With increasing every 1 percent in inbreeding, 4 g for birth weight, 20.3 g for weaning weight, 247 g for month 6 and 4.5 g for month 9, was decreased, respectively. The results of this study, confirm the low level of inbreeding in the herd. Applying a designed mating system like crossbreeding could be a suitable method to avoid inbreeding depression via keeping the level of inbreeding under control. The utilization of a program for directed mating in the present flock is an appropriate alternative to keep the level of inbreeding under control. Conclusion: The results of present experiment showed that the rate of inbreeding is very low and it is not worrying in Lorestan native sheep.