Polymorphism of insulin-like growth factor 1 gene and its relationship with reproductive performances and milk yield in Sarda dairy sheep

The aim of this research was to detect polymorphisms within the IGF-I gene in dairy sheep and to verify their influence on milk yield and reproductive performances. Four hundred Sarda ewes in their second lactation were selected from 2 farms. Their reproductive traits (fertility rate, interval in days from ram introduction to lambing and litter size) and milk yield were recorded, from the second to the fourth lactation. DNA was extracted from individual blood samples and subjected to amplification and sequencing of the IGF-I gene 5′ UTR and Exon 3 regions. Three polymorphic sites were recorded at positions g184028491C>G and g184028489C>T of the 5′UTR, and g184023223G>A of the Exon 3. The C allele at position g184028491 showed a significant association with higher fertility rate (P < 0.05) and a shorter interval in days from ram introduction to lambing (P < 0.01). In addition, a significant effect of the CC genotype was found with higher milk yield for P < 0.05 in the second and third lactation, and P < 0.01 in the fourth lactation compared to the other genotypes. Even, AA genotype at position g184023223 of the exon 3 showed a positive significant effect on milk yield for P < 0.05, in the second and third lactation, and for P < 0.01 in fourth lactation compared to the other genotypes. In conclusion the found SNPs showed a significant influence on reproductive performances and milk yield in Sarda sheep breed suggesting a possible application in sheep selection plans.