Older yet more attractive: Multiparous ewes are preferentially courted, and elicit more mountings and ejaculations than nulliparous ewes in group breeding

Abstract

High ewe density in group breeding enhances ram selectivity and favors the most attractive ewes. This study aimed to compare the sexual attractiveness of multiparous and nulliparous ewes. We hypothesize that multiparous ewes will be ranked as more attractive. Forty-two ewes, 21 multiparous and 21 nulliparous, Santa Ines × Dorper in estrus were tested. Each ewe was observed for five minutes, and behaviour was recorded from live and video observations. After each 5-minute test, the ewe courted for the longest time was removed and ranked as most attractive (rank 1), and this procedure continued until all six ewes in a group were ranked (1 = most to 6 = least attractive). Ewe ranking, ram behavior, and the odds of mounting acceptance were analyzed using the Friedman test, generalized mixed-effects models, and mixed-effects logistic regression, respectively. Mean attractiveness ranks were higher for multiparous than nulliparous ewes (2 ± 0.17 vs. 5 ± 0.17, P = 0.008). Rams also exhibited longer mean mounting duration (2.46 ± 0.91 s vs. 1.59 ± 0.91 s, P = 0.045) and a higher number of ejaculations (0.90 ± 0.31 vs. 0.14 ± 0.31, P = 0.0015) with multiparous ewes. While odds of accepting mounts were similar between categories (odds ratio = 0.45; 95 % CI: 0.08–2.75; P = 0.369). All first-ranked ewes were multiparous, and last two ranks were nulliparous. These results indicate multiparous estrous ewes as more attractive to rams, suggesting separating breeding groups per parity may improve fertilization rates in nulliparous ewes.