New polymorphisms at MTNR1A gene and their association with reproductive resumption in sarda breed sheep.

The aim of this study was to characterize the MTNR1A locus in Sarda sheep breed, in order to identify potential single nucleotide polymorphisms (SNPs) associated with reproductive resumption. The reproductive performance of 200 lactating ewes, aged 3-5 years, with body condition score (BCS) 2.5-4.0, at least at their third lambing were monitored for two consecutive years. In both year the enrolled ewes were exposed for 100 days to 10 adult, fertile rams. Mating, pregnancy and lambing for each ewe were recorded in order to evaluate differences in reproductive performance according to the analysed genotypes. From individual blood samples, DNA was extracted to amplify and to sequence promotor, the coding region, a part of intron and of 3' Untranslated region (3' UTR) of the MTNR1A gene. A total number of 29 SNPs were found (named SNP1 to SNP29), five of which caused also amino acid changes. The polymorphic sites found at positions g.17355452C > T (SNP16, rs430181568) and g.17355358C > T (SNP17, rs407388227) were linked (D' = 1 and r2 = 1) and showed a significant association to DRIL trait (distance in days from ram introduction to lambing). In both years, the ewes carrying C/C genotype in both these polymorphic sites showed the lowest DRIL compared to the other genotypes (P < 0.05). The ewes carrying C/C and T/C genotype exhibited the lambing peak at 170 days, and approximately 60% of the total lambing at 180 days from the ram introduction. Instead, ewes carrying T/T genotype showed the lambing peak around 200 days after ram introduction. Six haplotypes have been identified and the most frequent haplotype was also associated with lower DRIL (P < 0.05). Litter size displayed no statistical significance either among genotypes or among haplotypes. This study provided the major part of the MTNR1A gene in Sarda sheep breed and evidenced that SNP17 is associated with a shorter DRIL. The obtained results underlined the role of this polymorphism in improving reproductive efficiency in Sarda sheep and provides a suitable information for improving genetic selection.

Reproductive response to male joining with ewes with different allelic variants of the MTNR1A gene.

The aims were to evaluate the reproductive response to ram placement with Sarda ewes with different allelic variants at position g.15099485 A > G of the MTNR1 A gene. Ram placements occurred between the early and late spring and there was analysis of whether this polymorphism is associated with other nucleotide substitutions. In each of the eight farms where the study was conducted (named F1-F8), 150 ewes (50 with A/A, A/G and G/G genotypes) were selected. In each group of 150 ewes, eight males were joined with ewes on the following dates: 25 March (T1) for F1-F2, 15 April (T2) for F3-F4, 5 May (T3) for F5-F6, and 1 June (T4) for F7-F8. The lambing dates and number of new born lambs were recorded until 220 days after joining rams with ewes. The ewes with G/G or A/G genotypes had a greater fertility rate compared with those with A/A in T1, T2 (P < 0.01), and in T3 and T4 (P < 0.05). The duration of time in days from the time of ram joining with ewes to lambing was less in the ewes with G/G and A/G compared with those with A/A (P < 0.01). The g.15099485A>G variation was always associated with that at position g.15099391G>A. Results indicate there is a positive effect of the g.15099485A>G variant on reproduction when males were joined with ewes in March or April. The association that was ascertained in this study between the g.15099391G>A and g.15099485A>G polymorphisms for the MTNR1 A gene, could provide new insights to clarify the mechanism of action of melatonin.

Melatonin treatment in winter and spring and reproductive recovery in Sarda breed sheep.

This study aimed to evaluate the effect of melatonin treatment carried out between late winter and early spring on reproductive response in Sarda breed sheep and whether the photo-refractoriness can influence this reproductive response. The study was conducted on 3200 adult ewes, aged 3-6years old, with body condition score (BCS) 2.5-4.0, from 16 commercial sheep farms in Northern Sardinia. In each farm 200 animals were enrolled and subdivided into 2 groups (n=100 each): Group M (treated with one 18mg melatonin implant), and group C (untreated). The melatonin treatments were performed on 10th February; 10th March; 10th April and on 10th May each time in 4 different randomly selected farms. Adult males, treated with 3 melatonin implants 1 week before females, were introduced in each flock 35days after ewes' treatment, and removed after 45days of cohabitation with females. Pregnancy was determined by transabdominal ultrasonography examination between 45th and 90th day after ram introduction. Data showed that melatonin treatment increased the fertility rate significantly (P<0.05), with the higher fertility rate in the ewes treated in April and May. The average time in days from male introduction to lambing was shorter in treated than in control ewes (P<0.05). Further, at the 160th and 170th day after male introduction the group M showed a higher number of lambed ewes compared to C (P<0.01). This effect was observed at 180th and 190th days after ram introduction, also, but with lower significance (P<0.05). In conclusion, melatonin treatment improved reproductive efficiency and advanced breeding season in Sarda sheep, especially when ewes were treated in spring.