Repeated copulations with individual ewes by rams differing in level of
sexual performance
E.O. Price1, R. Borgwardt1, M.R. Dally1 and P.H. Hemsworth2. 1University
of California, Davis, CA 2Victorian Institute of Animal Science, Victoria,
Australia
The purpose of this study was to determine if rams differing in levels
of sexual performance differed in their tendency to repeatedly copulate
with individual ewes. Rams exhibiting relatively high levels of sexual
performance do not necessarily have a reproductive advantage if they repeatedly
inseminate the same females while other receptive females go unmated. Thirteen
high and 11 low-performing rams were individually exposed to 10 estrous
ewes in a small arena for 30 min on three occasions. Trials were terminated
once the rams had attained six ejaculations. (The high and low-performing
rams averaged 29 and 77 min, respectively, to attain the required six ejaculations.)
The two groups of rams investigated and courted an equal number of ewes.
However, the high-performing rams copulated fewer times with individual
ewes than the low-performing males (P<.01). As a result, high-performing
rams mated with a greater number of different ewes than low-performing
males (P<.06). These results indicate that high-performing rams are
more likely than low-performing rams to direct their attention to different
ewes after a successful mating. This tendency together with a faster rate
of ejaculation further validates the superior mating ability of high-performing
rams and underscores the advantage of using high-performing males in sheep
breeding programs, particularly when the female- to-male is relatively
high.