Polymorphisms of the melatonin receptor 1A (MTNR1A) gene do not affect sexual activity, plasma testosterone concentrations or testicular characteristics of 8-month-old ram-lambs born in autumn

Abstract

Thirty-nine autumn-born ram-lambs were used to study whether polymorphisms of the melatonin receptor 1A (MTNR1A) gene influence some reproductive parameters of Oct-born ram-lambs at 8 months of age. Animals were genotyped for their RsaI (CC, n=24; CT, n=6; TT, n=9) and Mn1I (GG, n=27; GA, n=6; AA, n=6) allelic variants of the MTNR1A gene. Liveweight (LW) was recorded bi-weekly until Jun, and scrotal perimeter (SP) was recorded once per month. From mid-Jan, blood samples were collected weekly to measure plasma testosterone concentrations. In mid-Jun, individual serving-capacity tests were performed. Testicular ultrasonography was performed at the end of the experiment. The effects of the week and gene polymorphism on LW, scrotal perimeter, and plasma testosterone concentrations were evaluated statistically by the GLM for repeated measures procedure. LW, SP, and plasma testosterone concentrations were significantly (P<0.001) affected by week, but neither of the polymorphisms of the melatonin receptor 1A (MTNR1A) gene affected these variables. In the serving tests, genotypes did not differ significantly in individual behaviors or the number of events (CC: 24.1±3.2, CT: 26.3±13.0, TT: 16.8±4.8, GG: 22.0±3.0, GA: 21.0±6.7, AA: 27.8±12.7). Testicular features assessed by ultrasonography did not differ significantly among genotypes. In conclusion, the polymorphisms of the melatonin receptor 1A (MTNR1A) gene did not have an effect on the reproductive characteristics of autumn-born ram lambs, based on serving capacity tests, testosterone secretion, and testicular measurements at 8 months of age.

Genotyping of rams based on melatonin receptor 1A gene polymorphisms: a tool in sire selection?

“…Previous research by our group has shown that the T/T or the G/G genotype for the RsaI and MnlI polymorphisms, respectively, has a positive effect on the sexual performance of young and adult Rasa Aragonesa rams (Abecia et al 2020). Specifically, autumn-born ram lambs that carried the T/T or the G/G genotype were considerably younger at first mounting, while adult T/T and G/G rams exhibited a more intense reproductive behaviour than rams without these genotypes (Abecia et al 2020) although it was not associated with differences in social dominance (Abecia et al 2022). Moreover, the polymorphisms of the MTNR1A gene of rams seem to affect field fertility after artificial insemination (AI) depending on season (Abecia et al 2023), although the reason for these differences remains unknown.…”

Association of melatonin receptor 1 A with litter size in sheep: A review

“… 19 This includes the nuclei that are responsible for reproduction. 20 Preceding studies have revealed that the polymorphisms in the MTNR1A gene sequence have an effect on the ability of Rasa Aragonesa rams to reproduce both when they are young and when they are adults. 6 In particular, the T/T or G/G genotype was shown to be connected with earlier ram-lamb mating activity, and adult rams that carried the T/T or G/G genotype exhibited the highest reproductive behavior in the spring.…”

“… 6 In particular, the T/T or G/G genotype was shown to be connected with earlier ram-lamb mating activity, and adult rams that carried the T/T or G/G genotype exhibited the highest reproductive behavior in the spring. 20 …”