Further testing of Melatonin Receptor 1a for out-of-season reproduction in the Cornell flock and allelic frequencies compared with Romney sheep12

Abstract

Sheep are seasonally polyestrous breeders, meaning they breed when day length shortens in the autumn. Ewes respond to changing day length through chemical pathways involving melatonin receptors. Some breeds, such as Dorset, are known to be less seasonal with many ewes able to breed and lamb year-round. The Melatonin Receptor 1a () gene was identified as a candidate gene controlling out-of-season lambing. The first studies in the Cornell STAR accelerated lambing flock found that a allele was associated with a shorter time to first lambing and a shorter period between lambings. The favorable allele was denoted the allele and the unfavorable allele, the allele. This study evaluated additional data for the effect of the polymorphism on sheep reproduction. Genotypic frequencies among the 320 sheep in this study differed between Romney and breeds selected for accelerated lambing ( < 0.02), but they did not deviate from Hardy-Weinberg equilibrium. Using 228 ewes from the Cornell University flock, we found no association ( > 0.05) between the allele and success for out-of-season lambing and no significant differences were observed in several production measures, such as number of lambs delivered per yr or number of lambs weaned ( > 0.05). With few ewes in the flock, these results may be due to the high level of selection for accelerated lambing. This study shows that the allele may not be a beneficial marker for use within flocks seeking to improve production and the ability to lamb out-of-season. These findings warrant additional research on the genetics of aseasonality in sheep.

Seasonal Reproduction in Vertebrates: Melatonin Synthesis, Binding, and Functionality Using Tinbergen’s Four Questions

“…However, melatonin receptor subtype MTNR1A was not found to be expressed in kisspeptin neurons but MTNR1A was found in the ovine pars tuberalis to regulate prolactin, which has indirect effects on kisspeptin [ 204 ]. MTNR1A polymorphisms showed no significant relationship to “out-of-season lambing” [ 205 ]. When melatonin binds particular subtype receptors sheep, subsequent molecular and physiological responses are yet to be distinguished.…”

The effect of SNP rs400827589 in exon 2 of the MTNR1B gene on reproductive seasonality and litter size in sheep

“…Small Tail Han sheep, a local sheep breed in China, is characterized by high productivity and year‐round oestrus (Liu, Jiang, & Du, 2003), and the breed has been considered as a good source of ovine reproductive genes in China. In the early studies, studies reported that the relationship between polymorphism of MTNR1A and litter size and reproductive seasonality traits in different breeds of ruminants (Gunwant et al., 2018), such as sheep (Calvo et al., 2018; Chu et al., 2006, 2008; Mateescu, Lunsford, & Thonney, 2009; Notter et al, 2003; Pelletier et al., 2000; Posbergh, Murphy, & Thonney, 2017), goat (Abdolahi, Shokrollahi, Saadati, & Morammazi, 2019; Chu et al., 2007; Hua, 2006) and water buffalo (Gunwant et al., 2018). However, there are few reports about MTNR1B .…”