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.

Effect of Dorper Rams’ Social-Sexual Hierarchy on Their Sexual Behavior and Capacity to Induce Estrus in Ewes

“…For example, Bremner et al [30] mention that young men show a circadian rhythm in serum testosterone, with levels higher around 08:00 h and lower levels in the late afternoon, which would explain this difference in rams in the present study. High hierarchy rams have higher plasma testosterone concentrations [31], which is responsible for rams' sexual drive and smell, essential to generate a more potent stimulus to induce estrus in anestrus ewes [32].…”

Multiple matings modify the estrous length, the moment of ovulation, and the estradiol and LH patterns in ewes

“…The shortening of the period of behavioral estrus induced by repeated matings may have important implications in the sexual selection process. In polyandric species as sheep, rams compete for access to estrous females (Preston et al, 2001;Ungerfeld and Lacuesta, 2015). However, in competitive breedings, even in wild conditions or in farmed animals, the final individual progeny produced by different rams is influenced by their social behavior, but also by the direct impact of its mating dynamics.…”

Effects of testosterone administration and feeding level on reproductive activity in sexually inactive goat bucks

“…As it has been noted by Zarazaga et al (2009), in goat bucks, when the level of nutrition increased, sexual activity increased, too. Additionally, testosterone concentrations are directly linked to sexual and aggressive behavior in rams (Ungerfeld and Lacuesta, 2015).…”