Stallion Behavior Problems

By | 2012-10-25

This post briefly outlines several of the most common behavior problems of breeding stallions. These problems include self-mutilation, inadequate libido, rowdy breeding behavior, specific erection dysfunction, mounting and thrusting difficulties, frenzied hyperactive behavior, and specific ejaculation dysfunction. Also briefly outlined is the common problem of residual stallionlike behavior in geldings.

Inadequate Libido

Specific stallion libido problems include slow starting novices, slow or sour experienced stallions, and specific aversions or preferences. Although certain genetic lines tend to be shy or quiet breeders, the majority of inadequate libido in stallions is man-made in the sense that it is the result of domestic rearing, training, or breeding conditions. Stallions that have been disciplined for showing sexual interest in mares during their performance career, discouraged from showing spontaneous erection and masturbation, or mishandled during breeding under halter are at risk of libido problems. When exposed to a mare for teasing, stallions such as these may simply stand quietly, may appear anxious and confused, or may savage the mare.

Most stallions with such experience-related libido problems respond well to behavior therapy alone or in combination with anxiolytic medication. These stallions typically respond best to continued exposure to mares, initially with minimal human presence, and then with gradual introduction of quiet, respectful, patient, positive reinforcement-based handling. These stallions appear to respond favorably to reassurance for even small increments of improvement. Tolerance of minor misbehavior rather than punishment is often the most effective strategy with low-libido stallions. The anxiolytic diazepam (0.05 mg/kg through slow IV 5-7 min before breeding) is useful in about half of such cases as an adjunct to behavior modification.

Some libido problems are hormone-related, with androgens on the low side of the normal range. These stallions will likely improve with management aimed at increasing exposure to mares and reduced exposure to other stallions. This will typically increase androgen levels, general confidence, as well as sexual interest and arousal. Gonadotropin-releasing hormone (GnRH; 50 μg SQ 2 hr and again 1 hr before breeding) can be useful to boost libido in stallions, particularly in those with low normal levels. In rare cases when more rapid improvement is required to rescue a breeding career, treatment with testosterone can effectively jump-start a slow novice without apparent significant adverse effects on spermatogenesis. Current recommendations are 0.1 to 0.2 mg/kg aqueous testosterone SQ every other day for as long as 2 weeks, with frequent assay of circulating testosterone not to exceed 4 ng/ml.

Specific Erection Dysfunction

Libido-independent erection dysfunction is rare in stallions. The majority of erection dysfunction that does occur is related to traumatic damage of the corpora cavernosa that results in insufficient or asymmetric tumescence (lateral or ventral deviations) that impairs insertion. In some instances, penile injury appears to impair sensory and or proprioceptive feedback from the penis, delaying ejaculation, coupling, or organized thrusting. Common causes include stallion ring injuries, drug-related paralyzed penis and paraphimosis, kick injuries, and self-serve breeding dummy accidents.

An interesting and often confusing type of erection dysfunction involves the folding back of the penis within the prepuce. The behavioral hallmark of this situation is a stallion that appears aroused and ready to mount, without a visible erection. The stallion may also appear uncomfortable or intermittently distracted, pinning the ears, kicking toward the groin, and/or stepping gingerly on the hind legs. Close observation reveals a rounded, full-appearing prepuce, with the skin stretched taut. Resolution usually requires removal of the stallion from the mare until the penis detumesces. Once the penis is fully withdrawn, application of a lubricating ointment to the prepuce facilitates subsequent normal protrusion. This situation tends to repeat occasionally over time, particularly in stallions with profuse smegma production or with dryness of the penis and sheath from frequent cleansing.

Mounting And Thrusting Difficulties

A significant percentage of breeding dysfunction appears to involve neurologic or musculoskeletal problems that affect the stallion’s ability to mount and thrust. Many such stallions can continue breeding with therapy aimed to reduce discomfort and accommodate disabilities during breeding, including adjustments to the breeding schedule aimed at reducing the total amount of work. This author has found that long-term treatment with oral phenylbutazone (2-3 mg/kg orally twice daily) often works well to keep such stallions comfortable for breeding. Certain debilitated stallions can benefit from semen collection while standing on the ground.

Specific Ejaculation Dysfunction

Although any libido, erection, or mounting and thrusting problem can result in failure to ejaculate, stallions also exist in which the dysfunction seems to be specific to ejaculation. Specific ejaculation problems can include apparent

failure of the neural ejaculatory apparatus, physical or psychologic pain associated with ejaculation, and genital tract pathology. Goals of therapy are to address as many contributing conditions as possible, as well as to optimize handling and breeding conditions and maximize musculoskeletal fitness and libido to enhance the stallion’s ability to overcome ejaculatory difficulty. Imipramine hydrochloride (0.5-1.0 mg/kg orally 2 hr before breeding) can effectively reduce the ejaculatory threshold.

Rowdy Breeding Behavior

Rowdy, misbehaved breeding stallions in most cases represent a human-animal interaction problem. Most problems can be overcome with judicious, skillful, respectful re-training. Even strong, vigorous, and misbehaved stallions can be brought under control by using consistent positive and negative reinforcement, with very little or no severe punishment. Re-training can be done in a safe and systematic manner without abuse or commotion, usually within a few brief sessions. Some of the most challenging, rowdy stallions may benefit from vigorous exercise under saddle or ground work immediately before breeding. This practice not only fatigues the stallion but also establishes a pattern of the stallion taking direction from a handler. For similar reasons, this author recommends an intensive schedule for breeding shed retraining, with as many as several breedings per day. With fatigue and reduced urgency to breed, many stallions seem more able to abide direction and learn a routine. With rapid repetition, stallions seem to more readily understand the routine. Tranquilization is generally not recommended. Levels of sedation that improve controllability without compromising musculoskeletal stability or ejaculatory function are difficult to achieve. Tranquilizing agents commonly used in stallions, such as xylazine or detomidine, can both facilitate and inhibit erection and ejaculation depending on dose.

Frenzied Behavior

Distinct from simple rowdiness, some stallions are hyperactive or even frenzied. This is typically greater during the breeding season. Some will spend nearly their entire time budget frantically “climbing the walls,” or running a fence line. In general frenzied breeding stallions can benefit from more roughage and less grain in the diet, organized physical work and pasture exercise, and consistent housing in a quiet area. Careful observation (particularly video surveillance) can be useful to identify environmental conditions and events that set off episodes or tend to quiet a stallion. In extreme cases, pasturing directly with mares can effectively quiet or sensibly occupy a frenzied stallion. L-Tryptophan supplementation (1-2 g twice daily in feed) can have a calming effect on such stallions. Tranquilization for this purpose is not recommended in breeding stallions because of risk of paralyzed penis and paraphimosis.


Although not unique to stallions, self-mutilation is a severe and relatively uncommon fertility limiting and/or life-threatening problem. This behavior typically takes the form of self-biting of the flank, chest, or limbs, with violent spinning, kicking, and vocalization. Self-mutilation in horses appears to occur in two distinct forms. One appears to be a severe reaction to irritation or pain, and would be similar in males or females. The self-biting is typically targeted toward the site of discomfort. Another form occurs in males and is reminiscent of stallion intermale aggression. The behavior is targeted at the typically intermale sites of aggression — the groin, flank, knees, chest, and hocks. The sequence of the behavior follows closely to that of two males fighting, with sniffing and nipping of the groin, vocalization, stamping with a fore leg, kicking out with a hind leg, and then taking occasional larger bites from anywhere on the opponent’s body.

Episodes often appear to be stimulated by sight, sound, or smell (feces or oily residues) of another stallion. For some stallions, episodes are set off by sniffing their own excrement or oily residues on stall walls or doorways. Current recommendations to control episodes are as follows: (1) physically protect the stallion from injury by padding walls or limbs, blanketing, and muzzling as effective; (2) aggressively evaluate the housing and social environment to identify exacerbating and ameliorating conditions that may be manipulated for greatest relief; (3) reduce concentrates and increase grass and hay in the diet to increase feeding time and eliminate highly palatable meals (feeding tends to distract and occupy the stallion; concentrate meals tend to increase stereotypic behavior); (4) apply odor-masking agents (Vicks or Acclimate) around the nares; and (5) provide as much organized exercise as possible, also to distract the stallion.

Residual Stallionlike Behavior In Geldings

Castration, regardless of age or previous sexual experience, does not always eliminate stallionlike behavior in horses. If given the opportunity, as many as half of geldings will show stallionlike behavior to mares, many will herd mares, and even mount and appear to breed. Similarly, although castration does tend to “mellow” most horses, it does not eliminate general misbehavior. Traditional behavior modification is usually much more effective in the control of sexual and aggressive behavior in a gelding under saddle or in-hand than it is with an intact stallion. Also, treatment aimed at quieting sexual and aggressive behavior, such as progesterone (e.g., altrenogest, 50-75 mg orally daily), is typically more effective in geldings than in intact stallions. Elimination of stallionlike herding and teasing at pasture is difficult. Separation from mares is recommended.