Reproductive problems of stallions (Proceedings)


Reproductive problems of stallions occur frequently and may be related to physiologic, pathologic, and management processes. Relatively few colts are kept as stallions in the equine industry, and veterinarians may not have a great deal of exposure or experience with stallions.

Reproductive problems of stallions occur frequently and may be related to physiologic, pathologic, and management processes. Relatively few colts are kept as stallions in the equine industry, and veterinarians may not have a great deal of exposure or experience with stallions. There is a need to be familiar with the parameters, measurements and expectations for average fertility in stallions. Practitioners who work in the breeding industry need specific knowledge of the possible differential diagnoses for fertility problems, and must have an understanding of and be able to recognize common: fertility problems, injuries and neoplasms of stallions. This paper will discuss fertility parameters, etiology, diagnosis, treatment, and prognosis of common reproductive problems of stallions.

Stallions may be afflicted by a long and varied list of differentials that impact a stallion's fertility. The horse may have psychological, mechanical, or reproductive problems. A short list of common reproductive problems includes: Poor intrinsic fertility, Testicular Degeneration, Partial Ejaculation, Spermiostasis, STD's, Hemospermia / Urospermia, Trauma, Torsion, Tumours, and other infections (Ball 2008). Other conditions are also listed that may or may not influence fertility.


What is the average Fertility rate of Horses? Lessons from feral horses suggest that under good nutritional conditions horses may be very successful breeders, indeed in some circumstances, such as pasture breeding, they may achieve a greater than 90% pregnancy rate in 60 days rivaling fertility in beef cattle. On the other hand the typical domestic horse has not had a great deal of selection pressure to have high fertility. Feral stallions are typically paired with small harems of around 3 mares, that they would have the opportunity to breed over 1-2 estrus cycles (Feist and McCullough 1975). Feral horses therefore likely did not have intense evolutionary pressure to be exceptional breeders. Today the selection of commercial equine breeding stock is often based on the animals athletic performance, and with the exception of some Warmblood breeds, the focus is usually not fertility (Dowsett and Knott 1996; Einarsson, Dalin et al. 2009). Not focusing on fertility in the equine industry has resulted in per cycle pregnancy rates of 45 - 55% in a general population of mares, which is similar to the dairy industry. Calculations of per cycle and seasonal pregnancy rates need to include all mares, and it is not correct to exclude less than "normal mares." In terms of accuracy first cycle pregnancy rates are the best to use because they avoid the negative effects of the repeat breeding subfertile mares on a stallion`s apparent fertility. Average stallions breed relatively few mares (10 or less) so a per cycle pregnancy rate is usually used for the sake of a having a reasonable number of cycles in the calculation. Usually at least 25 cycles are required to estimate a stallion's fertility. Some choose to break down the results into mares with foals at foot versus barren mares. Seasonal pregnancy rates in horses should be above 85% in well - managed herds. The notable exception is the Thoroughbred breed where the seasonal pregnancy rate is 50 - 55%. Stallions are generally considered problematic and not suitable for commercial use if their per cycle pregnancy rate (PR) falls below 30%. The reason for this is that mares are rebred many more times and most mare owners are reluctant to breed their mare more than twice, due to later foaling dates

Poor intrinsic fertility

Young stallions may also have poor intrinsic fertility, which may be generally identified by a BSE. These stallions have no history of illness or trauma. Characteristics include: small soft testis, small total scrotal width (TSW) < 7 cm, low testicular volume, poor spermatozoa morphology, and low motility. They may have a specific morphologic defect that is present in a high percentage of sperm. If the stallion has no history of illness, injury etc., all medications such as anabolic steroids are discontinued, and a number of serial semen examinations spaced 2 months apart show the same results, the stallion probably has inherited genes that do not support good fertility. The stallion is an inefficient breeder but is not usually infertile (Brito 2007).


Means low sperm numbers. Many causes such as genetic, incomplete ejaculation, immaturity, small testis size, hypoplasia may explain low sperm numbers. Measure testis and determine his calculated Daily Sperm Output DSO based on testicular mass (LxWxH cm3) and compare it what he is producing. Necrospermia – high proportion of dead sperm, may be due to genetics, anabolic steroids, toxins, injury etc. Best to determine trends over time to determine if the problem is persisitent or transient.Teratospermia – high proportion of abnormal sperm, especially with bizarre shapes. May be anabolic steroids, genetics, toxins. Best to determine trends over time after removing any possible causes. Asthenospermia – immotile sperm live sperm, usually due to ultrastructural problems with dynein arms, or microtubular structure of the sperm. Need electronmicroscopy (TEM) or testicular biopsy to confirm. If immotile and dead then you have 2 problems. One error is that spermicidal lubricants are used, be sure that lubricants etc are non-spermicidal! Azospermia – no sperm. Rule out primary causes, such as failure of spermatogenesis (severe degeneration) versus secondary obstruction (ampullary blockage) and retrograde ejaculation into the bladder. Combinations of problems are sometimes noted together such as teratonecrospermia

Testicular degeneration

The cause of testicular degeneration may be traumatic, nutritional, toxic, genetic, parasitic, thermal, immune, or idiopathic. The most common type of testicular degeneration in the stallion is the idiopathic form. Older stallions are usually affected, however in some family lines an early senescence occurs. The process of degeneration has a variable time frame, where some stallions become subfertile (per cycle pregnancy rate less than 30%), and others rapidly become infertile. The Sertoli cells fail to function normally. Typically there are >10% germinal epithelial cells, and greater than 30% head, and 25% midpiece defects (Blanchard, Varner et al. 1992; Turner 2005).

Partial ejaculates

One of the main problems identified in older stallions include a loss of breeding vigour due to health related problems. Stallions are often neglected in terms of their health care, partly because people do not like to handle them. They are often overweight, out of shape, or foundered. They may suffer from chronic arthritis, chronic obstructive pulmonary disease, cardiac disease or hypothalamo pituitary dysfunction (adenomas). The desired number of urethral pulses is around 7. Stallions that are uncomfortable will deliver around 4 pulses. A thorough physical examination is warranted in older stallions. If trouble or reluctance to mount is a problem it will likely be worth looking for signs of laminitis, sore backs, etc. or using flexion testing of the hocks or possibly evaluating the stallion using radiography of the limbs. Many stallions require their hocks treated, or attention to previous athletic injuries such as carpal joint disease. They may benefit from non-steroidal anti-inflammatory drugs, hyaluronic acid, glycosaminoglycan therapy or steroid treatments, nutriceuticals such as glucosamine, therapeutic shoeing or combinations of these to improve their joint health and comfort. Massage and acupuncture may help manage pain in certain horses.


This condition is generally an acquired, dysfunction but may be found at the first BSE in a young stallion. This is a condition in horses where the stallions experience intermittent or complete obstruction of the ampulla on one or both sides. The effected stallions may intermittently ejaculate from one side or both sides. Less commonly spermiostasis may be noted as a transient condition. In spermiostatis the sperm accumulate in the ampulla. The ampulla may be enlarged and corded (>1.0 cm) on palpation. The lumen of the ampulla may appear corrugated and edematous on ultrasound examination. The stallion may have irregular spermiograms, such that when one of the occluded sides unblocks enormous numbers of senescent spermatozoa are released. The senescent sperm are dead sperm cells with detached heads. The treatment for this condition is frequent collection, manual massage, and/or exogenous oxytocin (20IU IV) given 10 minutes prior to collection. Alkaline phosphatase is elevated in the semen of stallions that are ejaculating.

Std's infectious causes of infertility

Infectious causes of infertility include seminal vesiculitis, orchitis, and epididymitis. These conditions usually cause pyospermia. Seminal vesiculitis is an infection of the glands typically from ascending bacterial infection. Local delivery of antibiotcics is required for treatment. The incidence of orchitis and epididymitis is very low and may be from ascending infections, or through external puncture wounds. Rarely parasite migration may cause problems in these tissues. Sexually transmitted diseases (STD's) have Bacterial, Viral, and Protozoal Causes.


In general STD's in horses are uncommon. The bacterial sexually transmitted diseases (STD's) arise from mostly Gram negative infections that cause seminal vesiculitis (Pseudomonas aeruginosa and Klebsiella pneumonia) or contagious bacteria that colonize the penile and preputial tissues (Taylorella equigenitalis). These represent persistent conditions with carrier states in the stallion.

The affected stallions with seminal vesiculitis shed bacteria into their semen with Pseudomonas aeruginosa and Klebsiella pneumonia being reported associated as common pathogens causing seminal vesiculitis other organisms include Streptococcus spp., Staphylococcus spp., Brucella abortus, and Acinetobacter calcoaceticus (Varner, Blanchard et al. 2000). Pseudomonas aeruginosa and Klebsiella pneumonia are ALSO often environmental contaminants and can be mistaken for pathogens. Therefore simply culturing them from a semen sample or the penile tissues may have no significance. It is significant when there are neutrophils in the semen, and mares bred with this semen develop signs of post breeding endometritis that MATCHES the organism obtained from the stallion. Cultures of a precollection urethral sample that does not have the pathogen, followed by a post collection sample of the urethra suggests the organism is being emitted with the semen. The history may also show that the mares bred to this stallion return to estrus early, or have a higher incidence of endometritis. These historical features are the indications that the stallion has a STD type problem. Best option is to refer the stallion or treat him using local delivery of antibiotics directly into the affected seminal vesicular glands using an endoscopic approach. Treating the semen with an extender that contains antibiotics effective against the organism is another option.

Another STD is caused by Taylorella equigenitalis, a Gram negative organism. This is a bacteria that causes a condition called contagious equine metritis (CEM). It may be spread from mares to stallions and vice versa. In stallions it colonizes the penile tissues, prepuce, and fossa glandis. It may be present in preseminal fluid. In mares it is present in the reproductive tract (uterus, cervix, vagina, clitoris) and particularly favours the clitoral sinus and clitoral fossae. This disease is present in Europe, was recently reported in the USA, but is not found in Canada. Infection results in a purulent endometritis in mares. Imported stallions from CEM affected regions should be quarantined and test bred to mares. A grey to creamy vulgar discharge mats the hair of the mare's buttocks and tail, although in many cases, the discharge is absent and the infection is not apparent. Most mares recover spontaneously, although many become carriers. Infected mares are usually infertile during the acute illness. However, the infertility only lasts a few weeks, after which pregnancy is possible. Stallions do not show signs of infection. The first indication of the carrier state is the appearance of Contagious Equine Metritis and/or lack of pregnancy in the mares covered by the stallion. The carrier state in stallions is usually eliminated with repeated treatment with topical treatment with 2% chlorhexidine of the stallion's penis/prepuce while aroused.

Viral std's

The viral STD's include EVA, and Equine Herpesvirus III.

Coital exanthema ehv iii

Coital Exanthema EHV III is a disease where stallions or mares may be carriers. In this disease the stallions develop blisters on their penis that when healed scabs and then depigmented non-raised spots that can be confused with precancerous SCC. In the acute blistering phase the stallion may refuse to breed and this prepuce may appear swollen.Transmission is not prevented by AI, and infections are self limiting in 1 – 3 weeks time. Infection of mares at the time of breeding doesn't interfere with pregnancy. Mares erupt a few days after breeding on the vulva and sometimes the anus with vesicles, which then rupture, and form scabs. Stress may cause a mare or stallion to recrudesce and shed the virus.

Equine viral arteritis

Cause by Equine Arteritis Virus (EAV), this virus infects young and mature horses. Not all exposed stallions will become chronic shedders of the virus in the semen. Infection in some breeds is widespread (standardbreds and warmbloods). The EAV is shed from the accessory sex glands of the shedder stallions and testosterone is needed for secretion, therefore gelding the shedding stallion stops venereal shedding. An infected stallion will have an EVA titer. There are no lesions present in the stallion. Common equipment and holding stalls may result in spread between stallions. Infected semen or AI equipment can spread the virus to mares. Virtually all naïve mares will seroconvert with 14 – 30 days if bred with EAV positive semen. The mares may shed the virus after the primary infection for weeks in bodily secretions. Infection does not prevent pregnancy. To determine if a stallion sheds EAV his semen must be tested. Presently there is a serologic test (titer) and pcr test available for blood. The venereal form of EAV is not usually associated with abortion, but the flu-like respiratory form is associated with abortion in naïve mares. Frozen semen may be one means of bringing the virus to a farm. There is a vaccine (killed) available in North America.

Protozoal – Dourine

Dourine is caused by Trypanosoma equiperdum. The disease affects horses, donkeys and mules. The disease is found in Europe, Asia, African and parts of the Middle East. Serology may be used to identify infected animals. T. equiperdum is found in the vaginal secretions of infected mares and the seminal fluid, mucous exudate of the penis, and sheath of stallions. Periodically, the parasites disappear from the genital tract and the animal becomes non-infectious for weeks to months. Non-infectious periods are more common late in the disease. Male donkeys can be asymptomatic carriers. Dourine is characterized mainly by swelling of the genitalia, cutaneous plaques and neurological signs (shifting weight, incoordination, facial paralysis). Genital edema and a mucopurulent discharge are often the first signs. Mares develop a mucopurulent vaginal discharge, and the vulva becomes edematous; this can be found in the vaginal secretions of infected mares and the seminal fluid, mucous exudate of the penis, and sheath of stallions. Pathognomonic lesions include raised plaques over the ribs 'silver dollar' lesions. Chronic debilitation and lymphadenopathy are common. Rarely, infected mares pass the infection to their foals, possibly before birth or through the milk. Infections


Smegma is a waxy secretion that is comprised of exfoliated skin and debris and is normally present in the sheath of stallions. Loose skin and debris also collects at the preputial ring, prepuce and on the penile shaft. Discharge from the sheath may be noted in some stallions or geldings and be evident on the horse's hind legs. Some discharge is attributed to normal preputial secretions, but excess secretion may accompany overzealous cleansing, bacterial overgrowth, balanitis, coital exanthema, foreign bodies, habronemiasis, and squamous cell carcinoma. Pruritis, inflammation and a hot moist dermatitis may be present in some cases. Bedding materials such as fine saw dust may be a problem. Treatments for bacterial balanitis include cleansing, antibiotics therapy, NSAIDs and in resistant cases immunomodulators and smegma transplants.


This is a condition where pure blood appears in the ejaculate. With live cover the history is that the stallion is covered with blood at the time of dismount. The stallion is asymptomatic when not aroused, but may drip blood with his preseminal fliud. Hemospermia afflicts Quarter Horses idiopathically, and others due to penile urethral injury (jumping over the fence with an erection, breeding through a fence). Arousal increases urethral pressure and the stallion emits blood from an urethral tear or granulomatous lesion. Endoscopic exam of the urethra is used to obtain a diagnosis, and especially to evaluate the severity of the condition. The stallion is sexually rested for 3 weeks if blood is still present wait 3 months. If blood is present after 3 months consider a perineal urethostomy.


May be a sporadic or persistent problem. Generally the stallion is trained to urinate immediately before breeding or AI collection to prevent the problem. Urine and sperm do not mix. Urospermia has been reported in stallions homozygous for Hyperkalemic Periodic Paralysis (HYPP). Urospermia may be noted clinically in stallions with COPD, where it is exertion related in these horses. Urine crystals or sediment are present in the semen. Stallions in the early stages of renal failure or those with other causes of PU PD may also have urospermia.


One of the more common presentations to veterinarians is trauma associated with breeding where mares injure stallions, often in the external preputial lamina. They often present with dramatic swelling to the point where the skin of the penis, prepuce and scrotum may crack, bleed and peel away. In examining these stallions it is important to determine the extent of the physical injury, swelling, trauma, hematoma formation, bruising etc. Determine if the sensory function of the penile and preputial tissue is within normal limits (hot then cold water test, noxious stimulation by pinching with forceps etc. Does the stallion have normal penile sensation? Does he withdraw his penis in response to pinching or cold water hosing? Determine if you have an injury that results in mechanical factors preventing penile or preputial retraction. Is the swelling preventing the penis from retracting? Or is the penis physically able to be replaced in the sheath but the stallion is unable to keep it that way? Injuries to the penis may result in chronic penile deviations (phallocampsis) when the stallion has an erection. Stallions with Phallocampsis are taught to mount in a fashion that aids intromission or collection.


Hematoma of the scrotum or testis results in a concern over damage to the "Blood Testis Barrier," Antisperm antibodies if produced could harm the stallion's sperm. The anti sperm antibodies opsonise the sperm make them easier to phagocytose. Symptomatic care of the exposed tissue is required. This includes hydrotherapy, emollient treatment (Zincofax) and tissue protection (kling and tensor type wraps).

Paraphimosis is when the penis cannot be retracted within the prepuce. In stallions the condition is usually caused by a breeding injury is more correctly termed Balanoposthitis (inflammation of the penis - prepuce). The swelling mechanically prevents the penis from retracting. The condition is treated by symptomatic care. This includes therapy to decrease tissue edema and hematoma formation. The goal is to replace the penis into the internal and external preputial cavity as fast as possible. Therapy for injured stallions usually includes: daily or twice daily exercise 10 – 15 minutes at a canter or trot, Hydrotherapy SID or BID to encourage circulation and aid in wound healing, NSAID phenylbutazone 1 – 4 grams daily as needed, SID BID, pressure wrapping – apply an emollient then tightly wrap using a tensor (reuseable elastic bandage) from the glans penis up the shaft. Use 3 layers of tensors, applied very tightly. Leave wrap in place for 15 – 20 minutes SID to BID. Repeat over a number of days. Mechanical support (stretchy porous material) mesh, or lingerie fabric, pantyhose, along with application of wound creams or DMSO, rest from sexual arousal and >3 weeks time for recovery. Occasionally diuretics, antibiotics and surgery are used.

Testicular torsion

Dynamic rotation of the testis occurs in some stallions, and is considered an unsoundness during a BSE. Testicular torsion maybe an incidental finding during a BSE, cauda epididymides is/are located cranially. Excessive torsion causing vascular compromise, results in acute pain, colic like signs, and infarction of the testis. The stallions have colic like signs. Severe torsion requires surgery as it results in infarction, prophylactic orchipexy has been described.

Tumours of the penis and prepuce

Squamous cell carcinoma is the most common tumour of the external genitalia in horses. Breeds of horses with little skin pigment such as appaloosas, and paint horses, or light coloured horses such as cremellos, or buckskins are more commonly affected. Stallions and geldings are more commonly affected than mares. Typically there are multiple lesions located on the internal preputial lamina, penis and glans penis. Exposure to ultraviolet radiation from the sun is believed to be an inciting cause. Surgery including local excision, resection of the prepuce or penile amputation, cryotherapy, chemotherapy (topical 5-Fluorouracil), and radiation therapy have been used to treat lesions. Squamous papillomas often accompany squamous carcinoma. The invasive nature of this tumour may result in extensive tissue destruction, and malodorous bloody preputial discharge. These tumours have a low grade of malignancy and surgical excision is frequently used to treat the condition. Topical treatment of squamous papilloma lesions with 5-Fluorouracil has been successful. Tumours may be primary or secondary. Melanoma - Melanoma is an invariably malignant condition in horses often found in grey horses. The tumours are common in the ventral tail region, preputial tissues, and perineal (perianal) tissue areas of grey horses. They are found in the parotid salivary gland. Melanomas are usually firm nodular dermal masses that are locally invasive, and over time metastasize. They are dark on cut section. Surgical removal or debulking or histamine (H2) receptor blockers (cimetidine) have been reported to control the spread of the tumours. Due to their slow growth they are usually left untreated.


Cutaneous lymphosarcoma may cause firm dermal masses in horses either focally or in a disseminated fashion. Diagnosis is made by biopsy and or aspiration.


Sarcoids are tumours that have 5 classifications: occult, verrucous, fibroblastic, nodular and mixed. They frequently occur on the head, limbs, and ventral abdomen of horses. They have been described on the prepuce of horses. Exposure to cattle or areas where cattle have been is a risk factor. Repeated sublesional injection with immunomodulators, cryotherapy and excision have been described.

Testicular tumors

The list of primary testicular tumours in the horse is fairly short. The tumour that is most common in the horse is the seminoma. Other tumours that have reported include: teratomas, Leydig cell, Sertoli cell, Mastocytoma, and leiomyomas. Ultrasound examination of the testis is very helpful in differentiating tumours, from orchitis or infarction such as caused by testicular torsion. Fine needle aspiration may be used to confirm the diagnosis. Unilateral castration to excise the tumour may induce testicular degeneration in the remaining testis. In all cases stallions undergoing surgical removal of the testis bearing the tumour will have impaired fertility due to the loss of the testis and the additional damage from the surgery.


Most common testicular tumour – it is highly aggressive and metastasizes. Therefore it is advisable to check the regional lymph nodes. The tumour arises from germinal epithelium. Teratomas are the next most common, usually in cryptorchid testis, it arises from pluripotential germinal cells.

Other problems include Hydrocoele – fluid in between parietal and vaginal tunics, where. >1cm is considered abnormal. The testes are difficult to palpate and the scrotum may appear enlarged. There may be climatic, such as prolonged hot weather, and breed factors that increase the prevalence of hydrocoeles.


Vascular dilations, may enlarge and interfere with normal counter current heat exchange between the testicular artery and veins. They may be caused by verminous processes, congenital or acquired. They may accompany tumours or mimic tumours.

Flaccid penile paralysis

This is common following chronic debilitation. It does not resolve even after the horse is refed and he gains weight. Other causes include penile trauma (such as trying to breed through a fence or a breeding related injury) prognosis is guarded as up to a year may be required for nerve regeneration. The penis is edematous and is flaccid. Topical treatment should be used to keep the skin soft.


Priapism is non-natural penile tumescence. The penis in these cases is hard like a wooden baseball bat. Priapism occurs secondary to drug administration (acepromazine induced priapism, or general anesthesia while the penis is out resulting in a compartmentalization of blood). This is treated by benztropine mesylate (8mg IV/500 kg), and/or by removal of sludged blood using pressured 1 liter bags of saline and through and through needle lavage if the condition is recent. Flushing of cavernus spaces, and surgery have also been reported. Support the penis once it softens following benztropine mesylate 8mg IV (cholingeric blocker) administration.

Behavioural problems

Inappropriate negative reinforcement of stallion behaviour. Harsh handling and punishment of displays of sexual behavior may lead to psychogenic ejaculatory failure. Stallions that had intense negative reinforcement (management errors) of their sexual behavior are often afraid to show libido. They may exhibit anxiety and may be assisted by the an anxieolytic dose of – 10 mg of Valium IV before being introduced to the breeding environment. Make sure the handler who has metted out the negative reinforcement is not anywhere nearby. Some 2-3 yr old stallions may exhibit submissive behaviour "chawing" (opening and closing their mouth, similar to a frightened foal) when near mares. Low libido runs in some family lines The stallion's method / exposure to mares is important in determining if this is a libido, health, or social issue. A 24 time lapse video of a stallion in a stall may show the stallion is capable of spontaneous erection and masturbation. Pasture mated stallions may have no interest in mares that are not ready to ovulate. Older stallions may have had a bad breeding accident, or they may be worn out by the breeding season. Some stallions develop pain, such as from sore hocks, and learn to associate it with the breeding act, so they may refuse to breed mares. Behavioural Abnormalities include poorly socialized stallions that do not respect limits when being handled by people or when around mares. Turn out of poorly socialized stallions with an aggressive group of pregnant mares usually is effective in readjusting their attitude. Going back to basics on ground manners is also very important.

Ejaculatory dysfunction includes a spectrum of problems such as failure to get an erection or a full erection (psychological or shunt formation) where the stallion does not bell his glans penis during breeding, failure to ejaculate (blockage, inexperience, or spermatogenic failure), and retrograde ejaculation. A solicitous mare in heat, a 24 time lapse camera of a stallion`s activity in a stall (establishes if he is able to get an erection), and alkaline phosphatase measurement in the fluid help determine the nature of the problem (lower in ampullary or epididymal blockage, higher in primary spermatogenic failure). The nature of azospermia in a stallion may be determined by seminal plasma alkaline phosphatase (SPAP) activity quantitated using a diluted sample in a serum clinical chemistry machine. The results will be reported in IU/l, total SPAP activity then can be determined by multiplying the SPAP (IU/L) concentration by the volume of the ejaculate (L). When the SPAP is 1000 IU/l or total SPAP activity is 200 IU the result indicates that the sample contains fluid from the epididymides and testes signalling that a complete ejaculate has been obtained. Fertile stallions often have SPAP activities over 3000 IU/l, and total SPAP of 500 IU. If the SPAP activity is low, <100 IU/l, this indicates that the sample does not contain fluid from the epididymides and testis [eg, either a failure of ejaculation or a mechanical blockage (usually ampullary). When SPAP values are in between 100 and 1000 IU/L suggest either partial blockage, partial ejaculate, epididymal disease, or severe degeneration may be present (Turner 2005).

Anabolic steroid / glucocorticoid use

high percentage of abnormal spermatozoa, low motility. This may be confused with poor intrinsic fertility, poor sperm quality or with testicular degeneration. Serial examinations will show improvement if steroid use is discontinued and at least 3 months has elapsed. Full recovery may take up to 1 year (Danek 2008).

Habronemiasis – summer sores - of the prepuce or urethra.

Habronemiasis is a parasitic skin condition cause by the hatched larva or Drashia spp and Habronema spp. that result in a hypersensitivity reaction. Flies are attracted to moist tissue such as the prepuce and urethral opening where they lay their egss. The larvae invaid the skin. The lesions formed progress rapidly and are pyogranulomatous. Scrapings of the affected tissue may contain larvae. Biopsies have characteristic features such as a dramatic eosinophilic infiltrate, which is used to differentiate habronemiasis from squamous cell carcinoma. Yellow sulphur granules are present in the lesions. Complete blood counts may show systemic eosinophilia. Treatment is with ivermectin, organophosphate dewormers, or topical dewormers. Dexamethasone may be used to decrease the inflammation and response to larvae.

Unexplained subfertility. When the sperm looks good and mares still aren't getting pregnant, what now?

There are a number of causes of subfertility in the stallion including genetic, nutritional, degenerative, hormonal, parasitic, infectious, thermal, radiation induced, immune, neoplastic and idiopathic causes. Collection errors osmolarity and lubricants and Unexplained – semen looks good but doesn't get mares pregnant. Additional tests include: Special stains (Feulgen, acridine orange, chlortetracycline, PITC etc) to evaluate membrane function, Tranmission electron microscopy (TEM) of the sperm to evaluate the axoneme or the acrosome, Sperm chromatic structure assay SCSA, plasma membrane function tests (hyposmotic swelling test, sephadex glass wool), antisperm antibodies, acrosome reaction tests (A23187, progesterone, heparin), mitochondrial function tests, hormonal tests (FSH, LH, hCG response), testicular biopsy, and breeding trials.In vitro fertilization is used in other species but not the horse. Hyposmotic swelling test is used to evaluate membrane integrity. Sperm cells that swell are the ones with the intact membranes. Other fluorescent dyes are used to evaluate membrane integrity, chromatin, mitochondria etc. In the future genomics, proteomics, DNA microarrays may be used to identify problem stallions. Current in vitro tests only estimate fertility they do not predict fertility. There is no substitute for breeding mares. Tools such as cloning, and freezing/ harvesting of germ cells are used to circumvent male factor infertility in the future.


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