Ewes prefer subordinate rather than dominant rams as sexual partners

The Social Dominance of the Rams Did Not Influence Their Sexual Behavior but Did Affect the Number of Lambs Sired and the Lambing Rates

The objective of this study was to evaluate the sexual behavior of rams based on their social dominance (SD) when paired into dyads consisting of dominant rams (DRams) and subordinate rams (SRams) across two breeding seasons (BS) and to assess its impact on the number of lambs sired and lambing rate. Twelve adult rams (six dyads per BS) were used and introduced to 17 and 18 ewes during the summer breeding (SumB) and winter breeding (WinB) seasons, respectively. There were no differences in SD, except for the flehmen response (p < 0.0001). Significant differences (p < 0.05) were found in body development and scrotal circumference, as well as in the sexual inspection traits between BS and ram group. The breeding week influenced each sexual behavior variable (p < 0.05). A higher percentage of single lambing was observed in WinB (46.2%) compared to SumB (27.4%) (p < 0.05). SD had an effect on the type of lambing (p < 0.05), with DRams exhibiting 35.6% twin lambing, while SRams showed only 10.6%. In conclusion, SD did not impact the sexual behavior of hair rams. SD influenced the lambing rate, with DRams producing a higher percentage of twin lambs compared to SRams in hair ewes during the breeding season.

Determinants of ram sexual behavior and its impact on sheep breeding

In sheep, anatomical characteristics of the cervix and animal value limit application of reproductive technologies; therefore, most breeding is natural service. Rams are selected based on desired physical traits and semen capacity, but their contribution to flock genetics is constrained by expression of sexual behavior. In 1964, it was first reported that approximately one-third of rams expressed limited sexual interest toward ewes in estrus. Therefore, if rams were evaluated for expression of sexual behavior, it is estimated that as many rams would be culled for the lack of behavior as are currently culled for semen quality or physical deficiencies. Sexual behavior is complex, requiring sensory recognition and processing, integration of ram cohorts and social dominance, female mate choice, and a physical response. This review of the literature aims to provide insights into factors influencing expression of ram sexual behavior.

Rams' reproductive status during a controlled breeding period: effect of social dominance

The aim of this study was to compare the variation in body weight, scrotal circumference (SC), and seminal quality during a breeding period in dominant and subordinate rams. Data were collected from 12 dyads of rams, each bred with 15 ewes for 7 weeks. Before joining, the dominance relationship between both rams from each dyad was determined. Body weight and SC were recorded weekly in the morning, and semen was collected by electroejaculation, determining the volume, sperm concentration, mass motility, and percentage of sperm with progressive motility. In addition, the total number of sperm and sperm with progressive motility ejaculated were calculated. Dominance had no direct effect or interaction with time on any of the variables analyzed. Body weight, seminal volume, sperm concentration, mass motility, percentage of sperm with progressive motility, and total ejaculated sperm varied with time (p < 0.05), and scrotal circumference and total ejaculated sperm with progressive motility tended to vary with time. In general, all indicators evaluated were affected in the first weeks, when most ewes were cycling, recovering as the breeding progressed. It was concluded that, at least under the conditions of this study, dominance position did not affect the profile of the reproductive variables evaluated, although all of them were affected during the breeding period.