Multiparous ewes have greater mating success when competing with nulliparous ones

The hypothesis of this study was that multiparous ewes are more attractive to rams than nulliparous ewes, leading to more intense courtship and mating displays by rams in competitive environments. Thus, this study aimed to compare the sexual interactions of multiparous or nulliparous estrous ewes tested together or individually with sexually active males. Seven sexually experienced Corriedale rams, 21 multiparous, and 21 nulliparous Corriedale ewes were used. Competitive and individual sexual behavior tests were performed for 3 consecutive days immediately after estrous detection. Seven rams were tested with seven different dyads of one multiparous and one nulliparous female daily, totaling 14 ewes per day. The competitive sexual behavioral test evaluated a ram together in a pen with one multiparous ewe and one nulliparous ewe for 10 min. In the individual sexual behavioral test, each ram was tested twice for 10 min, with the same multiparous and nulliparous females used in the competitive sexual tests. The sexual behaviors of rams were recorded in both tests, and ewes' behaviors were registered in the competitive sexual tests. During the competitive sexual tests, rams approached, mated, and tended to sniff the multiparous ewes before the nulliparous ewes (p=0.03; p=0.01; p=0.056, respectively). In those tests, rams mated the multiparous ewes more efficiently than nulliparous ones (p=0.002), meaning that rams mounted multiparous fewer times to ejaculate. The number of flehmens and their length were greater in nulliparous than in multiparous (0.01 and 0.002, respectively). The nulliparous ewes urinated more times and tended to do it in greater duration and tended to walk more than the multiparous (p=0.01; p=0.06; p=0.08, respectively). During the individual sexual behavioral tests, rams showed no differences in the sexual behaviors displayed toward multiparous and nulliparous females. In conclusion, multiparous ewes were preferred as sexual partners over nulliparous ewes, with rams showing greater efficiency in ejaculating with multiparous ewes. This increased sexual attractiveness was primarily due to the ewes' attractive signals rather than their proceptive behaviors. However, multiparous and nulliparous ewes were courted and mated similarly when rams had no choice, increasing the likelihood of reproduction in both groups. While nulliparous ewes signaled their reproductive status more frequently through urination, this signal did not compensate for the other signals provided by multiparous ewes, which contributed to their higher sexual attractiveness. These findings offer practical insights, emphasizing the importance of separating multiparous and nulliparous ewes to optimize reproductive outcomes in collective breedings.