Polymorphisms of the melatonin receptor 1A (MTNR1A) gene affect the sexual performance of Rasa Aragonesa rams without changing their social dominance

This study aimed to investigate whether a specific genotype of the MTNR1A gene influences social dominance and reproductive performance in rams. Thirty-one rams were genotyped for Rsal and Mnll polymorphism of the gene: CC (n=19), CT (n=5), and TT (n=7), and GG (n=20), GA (n=6), or AA (n=5), respectively. Maintenance (standing still, lying down, drinking, feeding, walking, or stereotyping) and social behavior (agonistic and antagonistic interactions among rams) were recorded by direct observations involving instantaneous scan sampling and continuous behavior sampling. For each animal, his Index of Success (IS) and Displacement (ID) were calculated. One week after the social-behavioral observations, rams were tested in individual serving-capacity tests involving three ewes that were synchronized into estrus in a 15-m2 pen for 20 min. The genotypes did not differ in the number of aggressions they performed (CC: 88.95±12.85; CT: 106.20±21.00; TT: 70.43±8.50; GG: 76.05±8.72; GA: 119.00±16.16; AA: 95.80±36.39) or received (CC:75.79±5.82; CT:92.40±8.68; TT: 86.14±15.05; GG: 79.25±6.58; GA: 86.83±11.51; AA: 79.80±12.74), and their active and passive behaviors were similar. The genotypes did not differ significantly in IS or ID, and the proportion of rams in each success category was similar among groups. For the Rsal and Mnll polymorphism, TT and GG rams were responsible for 54% and 56% of recorded sexual events (P < 0.05), respectively. Results of this study confirm that the best sexual performance of rams was among those that carried certain genotypes of the MTNR1A gene. Still, it was not correlated with differences in social dominance.

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

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.