Investigation on lactation persistency and IGF-I gene polymorphisms in dairy sheep

Insulin-like growth factor I (IGF-I) plays an important role in mammary growth and function. We detected two novel SNPs in the 5 UTR of the IGF-I gene: g.855G>C and g.857G>A of locus X69472, and genotyped 103 sheep of three breeds at the identified polymorphisms. The same animals were genotyped at a previously reported SNP (g.271C>T; accession X69473) located in exon 3. From the SNPs we built 4 haplotypes. We calculated lactation persistency from test day records of the genotyped animals as the ratio of milk (kg), fat (g) and protein (g) yield from day 86 to 170 of machine milking to yields during the first 85 days of machine milking. We estimated allele substitution effect on persistency for each SNP and haplotype. We found that allele T of SNP g.271C>T and haplotype [G;T] had a positive effect on maintaining a constant yield level during lactation. The improvement of lactation persistency could be highly beneficial to the sustainable use of local breeds.