A polymorphism at the melatonin receptor 1A (MTNR1A) gene in Sarda ewes affects fertility after AI in the spring

The effect of MTNR1A gene polymorphisms on the fertility rate after AI in Sarda sheep was evaluated in 600 lactating adult ewes. Genomic DNA was subjected to amplification of the MTNR1A gene exon II. Amplicons were digested with restriction endonuclease MnlI. Ten samples from each genotype were sequenced. A polymorphism was detected (A612G) and ewes were determined to be +/+, +/- or -/- for the allele. Allelic frequency was 0.77 for the+allele and 0.23 for the-allele. The frequency of the +/+, +/- and -/- genotypes was 68, 19 and 13%, respectively. On 16 May 2009, 60 ewes from each genotype group were synchronised using intravaginal sponges containing 40 mg fluorogestone acetate for 14 days. At sponge removal, the ewes were administered 350 IU pregnant mare's serum gonadotropin and were then inseminated, 54-56 h later, with 400 x 10(6) spermatozoa. Pregnancies were confirmed 50 days after AI using transabdominal ultrasonography. Lambing dates and the number of newborn lambs were recorded within 155 days after AI. Conception and lambing rate were higher for ewes with the +/+ and +/- genotypes compared with those with the -/- genotype (P<0.01). In conclusion, there was a positive correlation between MTNR1A allele polymorphisms the reproductive response following synchronisation and AI in the spring.