The relationship between melatonin receptor 1A gene (MTNR1A) polymorphism and reproductive performance in Sarda breed sheep

Abstract

In several species the circadian changes in melatonin secretion acts as the organic informer of the photoperiodic trend. Some physiological functions, such as reproduction, are influenced by seasonal melatonin secretion. In small ruminants polymorphisms at the MTNR1A gene are associated with non-seasonal breeding. The aim of this research was to evaluate if the MTNR1A gene polymorphism influences first conception, second and third lambing in Sarda breed sheep. Two-hundred ewe lambs, born between 10th November and 10th December 2008, were randomly chosen from four selected farms and genotyped for the A612G polymorphism at the MTNR1A gene. To rule out a possible confounding effect of the low frequency of the A/A genotype in Sarda sheep, 800 ewe lambs were genotyped and 85 individuals were selected for each genotype (A/A, A/G and G/G). Fertile rams were given access to the selected ewe lambs from 30th July to 30th October 2009 during the first year, and from 1st May to 30th October 2010 and 2011 on the second and third year, respectively. Mating and lambing dates were recorded for each ewe during the three years. In the first year ewe lambs showed no differences among genotypes in their fertility rates, litter size and mean number of days from ram introduction to parturition. However, in the second and third year G/G and A/G genotypes showed, a shorter interval (expressed in days) from ram introduction to lambing, compared to A/A genotype (P<0.05). During the second year fertility rate for the G/G, A/G and A/A genotypes, were 91.7%, 90.2% and 89.9%, respectively; whereas in the third year fertility rates were 91.5% for G/G, 91.8% for A/G and 93.0% for A/A genotypes. We speculate that the similarity in fertility rates among different genotypes may be due to a carry-over effect because ew\\es carrying different genotypes were not separated. Results indicate that the MTNR1A gene polymorphism does not influence the onset of reproductive activity in Sarda ewe lambs, but this single nucleotide polymorphism (SNP) reveals its influence in the earlier reproductive resumption in the adult ewes. The interval from rams׳ introduction to lambing may be longer if animals with different genotypes were kept separated.