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مطالعۀ ژنتیکی شمارۀ سلول‌های سوماتیک با مدل تابعیت تصادفی روزآزمون در گاوهای شیری ایران

نوع مقاله: مقاله پژوهشی

نویسندگان

1 استادیار گروه علوم دامی، دانشکدۀ کشاورزی، دانشگاه کردستان، سنندج، ایران

2 دانشجوی دورۀ دکتری ژنتیک و اصلاح دام، دانشگاه کشاورزی و منابع طبیعی رامین خوزستان، اهواز، ایران

چکیده

پارامترهای ژنتیکی صفت شمارۀ سلول‏های سوماتیک جمعیت گاوهای شیری، با استفاده از رکوردهای روزآزمون جمع‌آوری‌شده توسط مرکز اصلاح نژاد دام ایران در سال‏های 1380 تا 1389 برآورد شد. داده‌ها شامل 222923 رکورد روزآزمون دورة اول شیردهی، متعلق به 29668 حیوان در 100 گلۀ مختلف بود. برآوردها با روش نمونه‌گیری گیبس و بر اساس یک مدل روزآزمون با تابعیت تصادفی انجام گرفت. منحنی شیردهی براساس چندجمله‌ای‌های لژاندر از روز شیردهی در مدل منظور شد. به‌منظور تصحیح اثر ناهمگنی واریانس باقیمانده، دورۀ شیردهی (5 تا 365 روز شیردهی) به 10 گروه با فواصل نامساوی دسته‏بندی شد. براساس نتایج، واریانس باقیمانده در ابتدای دوره بیشترین مقدار را داشت و از ماه دوم تا پایان دورۀ شیردهی روند کاهشی جزئی در این پارامتر مشاهده شد. کم‌بودن واریانس‏های باقیمانده و محیط دائمی و زیادبودن واریانس ژنتیکی، به افزایش وراثت‏پذیری در انتهای دوره انجامید. کمترین و بیشترین مقدار وراثت‏پذیری به ترتیب در روزهای 68 (031/0) و 365 (098/0) شیردهی مشاهده شد. همبستگی‏ ژنتیکی بین رکوردهای روزآزمون با افزایش فاصلۀ بین آن‌ها کاهش یافت. با استفاده از ضرایب تابعیت پیش‌بینی‌شده برای هر حیوان، ارزش اصلاحی روزانه و در نتیجه منحنی ژنتیکی در امتداد روزهای شیردهی ترسیم شد. روندهای ژنتیکی و فنوتیپی صفت نمرۀ سلول‏های سوماتیک، به ترتیب 0025/0- و 1075/- برآورد شدند (P<0.01). این نتایج نشان‌دهندۀ بهبودی مطلوب برای صفت نمرۀ سلول‌های سوماتیک در سطوح ژنتیکی و فنوتیپی است.

کلیدواژه‌ها


عنوان مقاله [English]

Genetic study of somatic cell score using random regression test day model in dairy cattle of Iran

نویسندگان [English]

  • Mohammad Razmkabir 1
  • Khabat Kheirabadi 2
1 Assistant Professor, Department of Animal Science, University of Kurdistan, Sanandaj, Iran
2 Ph.D. Student, Ramin University of Agriculture and Natural Resources of Khuzestan, Ahvaz, Iran
چکیده [English]

Genetic parameters were estimated for somatic cell score (SCS) in dairy cattle of Iran using test day records. The records of first lactation were extracted from the database of National Animal Breeding Center for cows calved between 2001 and 2010. Data included 222923 test-day records, obtained from 29668 animals distributed in 100 different herds. Estimates were carried out through Gibbs sampling procedures and using a random regression test-day model. Lactation curve were described in the model with orthogonal Legendre polynomials on days in milk. In order to correct for heterogeneity effect of residual variance, lactation period (5 to 365 days in milk) was classified into 10 groups with unequal distances. According to the results, residual variance was highest at the beginning and it was steady and decreased slowly from the second months to the end of lactation. Low residual and permanent environment variances and high genetic variance were lead to increase of heritability at the end of lactation. The lowest and the highest of heritability were at days 68 (0.031) and 365 (0.098), respectively. Genetic correlations between individual test-day records were high for adjacent tests and decreased as the interval between tests increased. Daily breeding values and genetic curve across lactation were produced for all animals using predicted regression coefficients. Estimation of genetic and phenotypic trends for SCS were -0.0025 and -0.1075, respectively (P<0.01). The results show a desirable improvement for somatic cell score at genetic and phenotypic levels.

کلیدواژه‌ها [English]

  • genetic trend
  • heritability
  • random regression model
  • somatic cell count
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