Spontaneous Erection and Masturbation in Equids

INTRODUCTION Spontaneous erection accompanied by an activity thought to be and referred to as masturbation occurs in stallions. Spontaneous erection involves extension of the penis from the prepuce with engorgement to its full length and rigidity, in a solitary, rather than heterosexual, context. The activity known as masturbation involves rhythmic bouncing, pressing, or sliding of the erect penis against the abdomen achieved by rhythmic contraction of the ischiocavernosus muscles and/or pelvic thrusting (Fig. 1). With such stimulation, the glans penis usually enlarges as during copulation, and presperm fluid may drip from the urethra. This behavior in horses seems analogous to spontaneous erection and masturbation noted in several other mammalian species. I-’ The significance of spontaneous erection and masturbation in horses, as in other species, is not well understood. Traditional views of spontaneous erection and masturbation in domestic horses follow those held for similar behavior observed in other domestic and captive wild animals. One theme is that these are aberrant behaviors, similar to other stable vices, resulting from regimentation or restricted activity of captive or domesticexistence. 4-6Another theme is that spontaneous erection and masturbation represent an expression or “venting” of sexual frustration resulting either from inherent hypersexuality or from thwarted access to heterosexual activity. 6v7Further, it has been asserted that masturbation limits the potential fertility of an individual stallion by depleting semen reserves and sexual energy. Accordingly, spontaneous erection and masturbation in horses are often discouraged. An array of management schemes and devices such as stallion rings, brushes, and cages have been employed to inhibit spontaneous erection and disrupt masturbation.8 Attempts to inhibit spontaneous erection and masturbation involve considerable management effort as well as risk of genital injury to the horse. This paper summarizes some of our recent studies as well as work in progress designed to characterize the frequency of occurrence and characteristics of spontaneous erection and masturbation in equids, from which are emerging convincing evidence that these activities represent normal equid behavior.