Competition Between Different Social Ranked Rams has Similar Effects on Testosterone and Sexual Behaviour Throughout the Year.

Abstract

Dominant rams have preferential access to females, as they frequently interrupt sexual behaviour from subordinated. Testosterone concentrations are directly linked to sexual and aggressive behaviour and have important variations along the year. Therefore, it may be expected that the effects of dominance relationships on reproductive behaviour differ according to testosterone concentrations, and thus to the period of the year. The aim of this study was to compare the effects of dominance relationships on testosterone and sexual behaviour in different moments of the year in rams. Twelve rams were maintained in a single group. Social rank was determined in January (maximum reproductive development), May (regression of the reproductive status) and August (lowest reproductive activity), and the four rams with higher (HR) and the four with lower (LR) success index were used. Testosterone serum concentration was weekly measured four times during each experimental period. Sexual behaviour was evaluated in each period with an oestrous ewe, and with the oestrous ewe and another ram from the other social rank (each HR with each LR ram). Testosterone concentration was greater in HR than LR rams in January (p = 0.03), and all the behaviours were displayed more frequently in non-competitive than in competitive tests (p < 0.05). Rams modified their sexual strategy in competitive environments decreasing the display of sexual behaviour independently of their social status. This effect was observed consistently throughout the year: high-ranked rams have greater testosterone concentrations than LR rams only during the pre-rut, when they naturally compete to join the groups of ewes.