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Analysis of IGF1 gene polymorphism and differences in litter size after first parity in Romanov sheep: preliminary results

Insulin-like growth factor 1 gene (IGF1 gene) controls the synthesis of insulin-like growth factor 1 (IGF1) which is involved in many physiological processes including reproduction. 5' flanking region of the ovine IGF1 gene is proven to be polymorphic, and the polymorphisms are associated with reproductive traits in some sheep breeds. The objectives of this study were to analyse ewes of high prolific breed with regard to their IGF1 genotype and litter size after first lambing. DNA was extracted from jugular vein blood of 22 Romanov ewes. Amplified PCR products of 5' flanking region of the ovine IGF1 gene were digested with HaeII restriction enzyme and allele and genotype frequencies were determined. Fischer-Freeman-Halton's test was used to test the differences in the number of ewes with specific birth type between observed genotypes. Determined level of significance was P<0.05. Digestion of PCR products with HaeII revealed three genotypes: AA, AB and BB. Allele A had a higher frequency (0.64) than allele B (0.36), and absolute genotype frequencies were as follows: AA (8), AB (12) and BB (2). Median, minimum and maximum for litter size after first parity for AA and AB genotyped ewes was 2 (1- 3), while within BB genotype one ewe had one lamb, and other two lambs. Multiple births (two or three lambs per litter) were observed in 87.5%, 75% and 50% of ewes within AA, AB and BB genotypes, respectively, and ewes with AA genotype had 12.5% and 25% more multiple births than AB and BB genotyped ewes, respectively. Observed differences were not significant (P>0.05). This preliminary study confirmed the presence of a polymorphism at 5' flanking region of the IGF1 gene in Romanov sheep. Absence of significant differences in birth type variation between genotypes may be due to the small number of animals involved, so further investigation with a larger number of sheep is recommended.

IGF1 gene, polymorphism, litter size

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