Tristan Starr, AI Technician, B.Sc.Agr (Hons)

Reproductive problems in the stallion can be divided into two sections, reproductive behaviour and reproductive disorders. Obviously, the first is caused by adverse behaviour of the stallion, and reproductive disorders are typically due to anatomical problems in the stallion. Any stallion presented with reproductive problems should be evaluated and examined prior to the beginning of the breeding season to ensure maximum fertility.

The purpose of a reproductive examination is to assess the stallion's ability to get a mare in foal and to identify probable causes of fertility problems. Relevant reproductive history such as previous fertility figures for mares, number of services per conception, number of services per foaling, behaviour at service and any previous reproductive examinations will aid the assessor in finding a cause for the problem.

Evaluation of reproductive behavior is an essential part of the breeding examination. An understanding of the stallion's behavior he displays in preparation for, during and after mating is important to diagnose disorders such as poor libido, erection failure and ejaculation failure. Sexual behavior dysfunction has been long recognised as the chief cause of equine reproduction failure. Therefore, it is extremely important to identify the variety of behavioural problems that cause the dysfunction, low sexual arousal, preferences to certain mares, preference for handlers or handling techniques, aggressiveness toward the mare or handler, self-mutilation, abnormal copulatory behavior, failure of erection or ejaculation and unmanageable behavior during mating. This being said some behavioural disorders are actually secondary problems caused by physical or anatomical troubles.


Poor Libido

A stallion's failure to show sexual interest in a mare is quite common in equine breeding. It is is often found in young or inexperienced stallions, overused stallions, stallions with a previous injury or timid stallions. Experienced breeders may show a decrease in sexual behavior by taking a longer to react when introduced to a mare or they may display a particular preference for a mare, location, handler or technique. Treatment for these problems requires patience and positive reinforcement. Changes to environment (housing near mares), handlers or reduced frequency of mating can improve the stallion's performance during the breeding season. Testosterone administration is also often used to increase the stallion's libido. However, this method is often subject to debate due to the adverse effects these drugs have on testicular function and increased aggressiveness, all without improving normal sexual behavior.

Erection Failure

Inadequate erection or loss of erection on insertion occurs in a small percentage of stallions. In most cases, erection failure is due to lack of libido or an underlying physical disorder caused by trauma. Failure of the stallion to mount or insert his penis may be due to lameness, spinal injury or again previous penile trauma. Treatment for these problems is aimed at the underlying cause and may consist of administration of anti-inflammatory drugs, reducing the number of mares served or training a stallion to ejaculate unmounted (this requires artificial semen collection and insemination).

Ejaculation Disorders

Ejaculation disorders are relatively common in the stallion, these include absence of ejaculation, incomplete ejaculation, premature ejaculation and urospremia (elimination of urine at ejaculation). Affected stallions often have increased libido and normal service behavior, including urethral pulsations, but they fail to ejaculate semen.

Painful conditions (back pain, lameness, bladder pain, painful conditions of the penis, testis and accessory glands) may result in hesitation during thrusting and poor stimulation. These conditions must be ruled out before any attempt to diagnose purely behavioural or psychogenic problems (the effect is psychological rather than physiological).

Primary psychogenic causes of ejaculation failure in stallions is generally a result of handling errors or unpleasant experiences during breeding or semen collection. Overuse of bits and chains when handling and controlling the stallion during collection or serving, forcing him to dismount immediately after ejaculation, slippery ground or mounting without an erection may lead to these problems. Treatment of psychogenic causes involves a combination of positive reinforcement, treatment with non-steroidal anti-inflammatory drugs and if collecting with and Artificial Vagina (AV) changing temperatures and pressure until it suits the stallion.

While assessing reproductive failure due to behavioural problems observation of the stallion's awareness of the mare, interest in precopulatory activity (sniffing, licking, nipping, Flehmen reaction), time taken to expose the penis and develop an erection, and desire to mount should be noted. Once the stallion is allowed to mount, make a note of any indication of pain or lameness, stability on hind legs and maintenance balance, ability to locate the mare's vulva, competence of thrusting, number of ejaculatory pulses of the urethra and dismount behavior. All this information will assist the examiner in diagnosing an accurate cause of the reproductive problem.


Disorders of the Scrotum

A 'normal' scrotum is soft, thin-walled with freely identifiable and moveable testes. Trauma, due to breeding injury, accident or foreign bodies, are the most prevalent problems associated with the scrotum. Scrotal trauma may result in haemorrhage, oedema or broken skin. If trauma to the scrotum occurs this in turn will disturb the thermoregulation of the testes, and cause reduced sperm motility and quantity.

Treatment for scrotal trauma is aimed at reducing inflammation without causing irritation or impaired testes function. Consult a veterinarian as soon as possible if scrotal trauma occurs to lessen the damage to sperm function.

Disorders of the Testes

These types of disorders can result from genetic abnormalities, anabolic steroid use or again trauma associated with injury. Cryptorchidism is among the most common disorders of the testes. It is the failure of one or both testes to descend into the scrotum. Retained testes cause the horse to develop male sexual behavior and secondary sexual characteristics but fail to produce live productive semen. A thorough examination needs to be performed to determine a diagnosis of cryptorchidism. In majority of cases the horses must have the testes surgically removed to reduce ongoing problems.

Testicular lacerations, another injury that can occur during breeding or may be due to blunt trauma, normally results in extensive internal bleeding. The prognosis for the testicle can be poor without immediate veterinary attention, if allowed to clot and produce fibrous tissue a decrease of thermoregulation will occur and castration is usually performed as a result.

Torsion of the spermatic cord around the scrotum will usually be noticed with the stallion showing signs of colic and scrotal pain. On closer inspection enlargement of the scrotum, increased scrotal fluid and thickened spermatic cord will be observed. Torsion may be 180 degrees, in which the testicle has a better chance of survival than 360 degree torsion, which usually results in castration. An ultrasound of the testicle and rectal palpation will be performed to diagnose the degree of torsion. Usually castration of the affected testes is carried out however if the affected testicle is still viable it may be corrected surgically and prevented from doing so again.

Anabolic steroid use in stallions has been of great debate for many years. It is common knowledge that treatment with anabolic steroids suppresses spermatogenesis (production of sperm within the testicle) and results in testicular degeneration, decreased sperm production and decreased testicular size in stallions. However, some may argue that the effects of steroid use are considered temporary in adults and the effect of anabolic steroids in the prepubescent colt is unknown. In a study completed by Squires et al (1981) it took the stallions treated with anabolic steroids 90 days to recover and produce a 'normal' sperm count. This is just one of many studies to be performed involving anabolic steroid use with similar outcomes in each study.

Testicular degeneration (TD) is a common cause of acquired and progressive infertility in stallions. TD may be temporary or permanent and may affect one or both testes depending on the overriding cause. Clinical findings include decreasing fertility, a decrease in testicular size and a decline in semen quality. Known causes of TD include thermal injury, infection, trauma, ionizing radiation, malnutrition, sperm outflow obstructions, and neoplasia. In these cases the length and severity of the cause of TD will determine the extent of the degeneration. Treatment for TD is aimed at removing the initiating cause, once this is removed TD generally doesn't progress.

Age related degeneration may also occur, but this is typically progressive and results in a steady decline in fertility. In some studies successful use of GnRH has been used as treatment for age related TD. However, these successes haven't been replicated in controlled studies and it is suggested that treatment with GnRH should commence before the testis reach a severe state of degeneration.

General treatment for TD centers on stallion management, a semen evaluation is imperative to ensure the stallion will be able to breed any number of mares within the breeding season and intensive mare management will assist in resulting pregnancies.

Disorders of the Penis and Accessory Sex Glands

Penile prolapse, paralysis, priapism (persistant erection without sexual stimuli), bacterial infection, EHV-3 (Equine Herpes Virus 3) and trauma are not generally common in stallions. If any of these conditions are to occur timely treatment will result in a successful outcome. Delayed recognition of penile disease or disorder can result in the need for aggressive surgical treatment which can interfere with the stallions future breeding career.

Majority of reproductive problems in the stallion are a result of reduced sexual behavior. Luckily these problems are the easiest to overcome with correct handling and collection of the stallion and with efficient semen processing techniques. A breeding soundness examination at the beginning of the breeding season will help 'iron out' any problems before they become too severe.

Figure 1: Stallion Reproductive Organs

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Tristan Starr: 0400 816 072
Mathew Holz: 0417 409 029

105 Chambers Road, Modella Victoria 3816

About Us

Tristan and Mat run the Stallion & AI Center during the breeding season and break-in, train and compete their own and clients horses all year round. Read more...