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.

中文翻译：

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MTNR1A基因的新多态性及其与sarda品种羊繁殖恢复的关系

本研究的目的是表征 Sarda 绵羊品种中的 MTNR1A 基因座，以确定与繁殖恢复相关的潜在单核苷酸多态性 (SNP)。对200头3-5岁、体况评分（BCS）2.5-4.0的泌乳母羊的繁殖性能进行了连续两年的监测。在这两年中，登记的母羊都与 10 只成年可育公羊接触 100 天。记录每只母羊的交配、怀孕和产羔，以根据分析的基因型评估繁殖性能的差异。从个体血液样本中提取 DNA 以对启动子、编码区、部分内含子和 MTNR1A 基因的 3' 非翻译区 (3' UTR) 进行扩增和测序。总共发现了 29 个 SNP（命名为 SNP1 到 SNP29），其中五个也引起了氨基酸变化。在位置 g.17355452C > T (SNP16, rs430181568) 和 g.17355358C > T (SNP17, rs407388227) 发现的多态位点是连锁的（D' = 1 和 r2 = 1），并显示出显着的关联（与 DRIL 的距离）从公羊引进到产羔的天数）。在这两年中，与其他基因型相比，在这两个多态性位点携带 C/C 基因型的母羊显示出最低的 DRIL（P < 0.05）。携带 C/C 和 T/C 基因型的母羊在 170 天出现产羔高峰，在公羊引入后 180 天出现产羔总数的约 60%。相反，携带 T/T 基因型的母羊在引入公羊后 200 天左右显示产羔高峰。已鉴定出六种单倍型，最常见的单倍型也与较低的 DRIL 相关（P < 0.05）。窝产仔数在基因型之间或单倍型之间均无统计学意义。该研究提供了 Sarda 绵羊品种中 MTNR1A 基因的主要部分，并证明 SNP17 与较短的 DRIL 相关。获得的结果强调了这种多态性在提高 Sarda 绵羊繁殖效率中的作用，并为改进遗传选择提供了合适的信息。