بررسي هم خوني و تأثير آن بر صفات رشد در گوسفند مغاني با استفاده از شجره

Inbreeding Investigation and its Effects on Growth Traits of Moghani Sheep Breed Using Pedigree

براي بررسي هم­خوني و تأثير آن بر صفات رشد از اطلاعات شجره 39408 رأس گوسفند مغاني كه طي سال­هاي 1365 تا 1394 در ايستگاه پرورش و اصلاح نژاد گوسفند مغاني جمع آوري شده بود، استفاده گرديد. براي آماده سازي، ويرايش داده­ها، برآورد ضريب هم­خوني و ميزان تابعيت صفات از هم­خوني به ترتيب از نرم افزار­هاي Fox Pro، Excel، CFC و Wombat استفاده شد. ميانگين نسل معادل كامل به عنوان معياري از كامل بودن شجره 1/60 بدست آمد. نتايج نشان داد كه 16/69 درصد از كل حيوانات، هم­خون بودند. ميانگين ضريب هم­خوني در كل جمعيت و حيوانات هم­خون به ترتيب 0/58 و 3/47 درصد محاسبه گرديد. در مدت سال­هاي مورد مطالعه، مقدار هم­خوني 0/047 درصد در سال افزايش يافت. بالا­ترين ميزان هم­خوني در گله 44/67 درصد بود. افت ناشي از هم­خوني به ازاي افزايش يك درصد هم­خوني براي صفات وزن تولد، شير­گيري، شش ماهگي، نه ماهگي و يك­سالگي به ترتيب 5/94-، 19/03-، 20/23-، 35/26- و 38/74- گرم برآورد شدند، كه به غير از صفات وزن شش ماهگي و يك­سالگي در بقيه صفات مورد مطالعه تأثير معني ­داري نداشت. نتايج اين پژوهش نشان داد كه اگر چه در اين گله طي سال­هاي مورد مطالعه بين حيوانات خويشاوند آميزش ­هايي صورت گرفته بود، ليكن مقدار ضرايب هم­خوني حيوانات هم­خون با توجه به تعداد اين دام­ها نشان داد كه در اين جمعيت آميزش­ ها هدف­دار و تا حد زيادي كنترل شده بود.

Introduction3 Moghani sheep breed with 2.5 million numbers is one the most important meat breeds among fatty tail sheep. The main center for keeping this breed is Moghan plain, but there is in the regions like Meshkin Shahr, Sarab, Ardabil and the other provinces. Inbreeding also impairs growth, production, health, reproduction and survival of inbred animals. A complete pedigree is also necessary for an accurate evaluation of inbreeding and other important population parameters. This research was done for pedigree analysis, estimation of inbreeding coefficient and investigation of its effect on growth traits by regarding to importance of growth traits in economic benefit of sheep farming. Materials and Methods Information of pedigree and growth traits (birth weight, weaning weight, 6 months weight, 9 months weight and 1 yearling weight) of available animals at breeding station of Moghani sheep were used for calculating of inbreeding and survey of its effects on growth traits of Moghani sheep. In this study, 16058 records of birth weight, 2145 weaning weight records, 2028 6 months weight records, 1319 records of 9 months weight and 1232 1 yearling weight records that were collected in 30 years (between 1987 to 2016) were used. For data preparation and editing and estimation of inbreeding coefficient Excel, Fox Pro and CFC soft wares were used respectively. For inbreeding effect analysis on related traits Wombat software and Restricted maximum likelihood method by using 12 animal models and considering of inbreeding in model as a covariate was used. The most appropriate model according to Akaike Criterion was selected. The statistical analysis of data was done by using of Duncan means test and GLM procedure of SAS 9.2 software. Results and Discussion In this research 48.30 % of animals have known sire and dam. The number of records of studied growth traits with age increasing had downward trend that may cause to elimination of some lambs or not registering of data in higher ages. For all of the traits, most of the animals had zero inbreeding coefficient, so that 83.31 % of population had zero inbreeding coefficient. 13.50 % of all population that is equivalent with 80.89 % of inbred population had inbreeding coefficient less than 5 %. In studied population, only 3.19 % of all population that is equivalent by 19.11 % of inbred population had inbreeding coefficient more than 5 %. Generation interval in four pathway including sire-son, sire-daughter, dam-son and dam-daughter was calculated 3.15 ± 0.053, 3.26 ± 0.093, 3.46 ± 0.015 and 3.57 ± 0.036 years respectively. Average generation interval of dam-progeny (3.51 ± 0.007 years) rather than sire-progeny (3.21 ± 0.064 years) was more. The shorter generation interval in sire-progeny pathway may be related to difference in replacement age of males and females. In other words, sooner replacement of males in studied herd might be one of reasons for shorter generation interval in sire-progeny pathway. The average generation interval was estimated 3.36 ± 0.069 years. In all of traits, the non inbreds had more average compare with inbreeds. In this study, male lambs in all traits had more average compare with female lambs that showed effects of sex on growth traits of Moghani lambs. The traits average of single lambs was more than twin lambs that may be related to more utilization of these lambs of maternal abilities. The results showed that 16.69 % of all population were inbred. The average of total population inbreeding coefficient was estimated 0.58 % that was in reported results range for this breed in other researches. The average inbreeding coefficient in inbred population and the highest inbreeding amount in herd was 3.47 and 44.67 % respectively. By evaluation of studied population form current generation to primary generation, decreasing trend in animals’ number was observed that may be related to a greater number of animals with known parents in current generation. The effective number of population was estimated 177.37. With reducing of effective number in population, the amount of inbreeding will increase. The increasing amount of inbreeding was 0.047 % in each year that was not significant. The inbreeding trend in studied years was positive and ascending with low swings. Average equivalent complete generations as a scale of pedigree completeness estimated 1.60. The low amount of equivalent complete generations can be related to incomplete and low depth of pedigree. The low effective number of population resulted in decreasing of genetic variation. Inbreeding depression for 1 % inbreeding for birth weight, weaning weight, 6 months weight, 9 months weight and 1 yearling weight were estimated 5.94, 19.03, 20.23, 35.26 and 38.74 gram that except 6 months weight and 1 yearling weight had not significant effect on the other traits. Having not a significant effect of inbreeding on birth weight, weaning weight and 9 months weight may cause to low level of inbreeding in herd and the low existence of dominance at controller genets of these traits. Regarding to the little effect of inbreeding depression on studied traits that is an optimal subject, it can be suggested by being low rate of inbreeding in this population, this trend persist in future years. Conclusion By regarding the significant effect of inbreeding on some growth traits and for prevention of undesirable effects of inbreeding, it can be recommended an ongoing supervision be done on related parameters to genetic variation at this population to Reduce the genetic diversity caused by increased inbreeding.