Ewes express increased proceptive behavior toward high-sexually active rams

Abstract

Variable expression of male reproductive behavior has been observed in all species studied. Approximately 25% of male sheep exhibit low sexual interest, but usually mate and have limited numbers of offspring. In domesticated, promiscuous species like sheep, the female may have mate preference, but mate choice is usually constrained by breeding strategies. It was hypothesized that when mate choice is limited, ewes would exhibit more proceptive behavior toward rams with low sexual interest to ensure reproductive success. Recorded serving capacity tests (n = 56) were utilized for this analysis. Rams were individually exposed to two ewes in estrus with behavior recorded for 20 min. From those recordings, a 10 min time period was utilized to assess ewe proceptive behavior. Ram anticipatory and consumatory behaviors were recorded. Anticpatory behaviors included ano-genitial sniffs, vocalization, fore-leg kicks, head butts, and nudges. Consumatory behavior included mount attempts, mounts, and ejaculations. Rams were categorized as high performing if they achieved two or more mounts during the 10 min period. Ewe behavior was determined by the number of solicitation looks and movements toward and away from the ram. During the 10 min of observed behavior, time spent in close proximity (less than 0.3 m) to the ram was determined and considered time in affiliation with the ram. Percent of time spent in affiliation with high sexually performing rams was greater (P < 0.001) 57.7% (±3.3) than when exposed to rams exhibiting low sexual behavior (23.8% [±3.4]). Affiliation time was highly correlated (P < 0.001; r2 ≥ 0.6) with ram behaviors: number of mounts, total anticipatory, and consummatory behavior. High sexually performing rams garnered more (P < 0.001) solicitous looks from ewe than did low performing rams. Ewes exhibited increased number of purposeful moves toward (P = 0.02), but not away (P = 0.58) from, high performing rams. These data indicate that ewes express more proceptive behavior toward rams expressing greater sexual interest. In conclusion, ewe behavior does not compensate for low sexual interest from the ram and would not be expected to contribute to the reproductive success of rams expressing low sexual interest.