Some studies of comparative aspects of sexual behaviour in ponies and donkeys

Abstract

The external manifestations of oestrus are said to be characteristic of the species. A comparative study of the cyclic sexual behaviour of eight pony mares ( Equus caballus) and five donkey mares ( Equus asinus) demonstrated significant differences in the signs of oestrus in the two species. A scoring system was designed to quantify the intensity of oestrus. In the pony, a maximum positive score was obtained when the mare showed an obvious interest in the stallion, adopted an acceptance stance with the tail held away from the perineum, and repeatedly retracted the vulval lips to evert the clitoris, often squirting out small amounts of urine or mucus. Aggressive or threatening behaviour, with the tail swishing or clamped against the perineum, received a negative score. This scoring system was then adapted to the sexual behaviour of the donkey. The most significant difference was that during oestrus the donkey mares exhibited a characteristic facial expression, involving a repeated raising and lowering of the mandible with the neck extended and ears depressed, when stimulated by the sight or sound of the stallion.