Mounting exhibited between cows is not associated with sexual motivation

Females of various species exhibit mounting behavior toward other mature females, i.e., female–female (f–f) mounting. Cows exhibit f–f mounting, which is commonly considered a sexual behavior based on a few similarities with male sexual mounting. Here, we hypothesized that the degree of f–f mounting exhibited by cows in estrus would increase when they are sexually motivated by sexually relevant stimuli. To test this hypothesis, two groups of four cows each were prepared. First, estrus was induced in one of the cows in each group by injecting estradiol in the presence of a non-sexually active male steer as a stimulus animal (steer-stimulus condition), and all f–f mounts were recorded. Estrus induction was repeated until induced in all cows. We then changed the stimulus animal from the steer to a sexually active bull (bull-stimulus condition), and the estrus induction procedures were repeated as before. We confirmed that estrus was induced successfully in cows injected with estradiol and that they were sexually motivated by switching the stimulus animal from steer to bull, as they spent relatively more time with the stimulus animal in the bull-stimulus than in the steer-stimulus condition and when not in estrus. However, f–f mounting frequency in the bull-stimulus condition showed no significant difference to that in the steer-stimulus condition. We observed that six of the eight subjects exhibited f–f mounting when not in estrus, which accounted for 44.6 % of f–f mounting we observed (n = 668). These findings suggest that f–f mounting in cows is not associated with sexual motivation.