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Examination of the sheath, penis and testicles can be likened to a “well man check” for horses. Just like dental checks, foot care, vaccinations and worm control, it’s an essential part of routine healthcare.

But many horses are not co-operative enough to allow a thorough and safe check inside the sheath (sometimes called the prepuce) without sedation, so vet assistance is advisable to allow early disease detection and treatment.

Unless an owner has specific concerns, a once-a-year check should be sufficient for horses less than 15 years old — or every six months for the older horse.

Infections of the sheath
Smegma is an accumulation of secretions, dead cells and debris inside the sheath.

Although older geldings will produce more smegma, most male horses do not need regular sheath and penis cleaning. Overzealous cleaning can cause detrimental changes to the protective microflora of bacteria that live in the sheath, increasing susceptibility to infections that can be hard to treat.

Some horses develop excess foul-smelling smegma that causes a dark-coloured discharge, sometimes seen on the inside of the horse’s thighs due to the sheath catching the legs when he lies down. This warrants initial veterinary examination to identify any underlying or associated conditions, and a programme to control the problem, often involving regular sheath cleaning.

For routine cleaning, use warm water only or a proprietary non-bactericidal, soap-based sheath cleaner.

An accumulation of smegma, referred to as a bean, can occur inside the end of the horse’s penis. If it reaches a size sufficient to cause discomfort, it should be removed by a vet.

Horses that tend to urinate from the sheath without protruding the penis can develop urine scalding, making them more susceptible to sheath infections and possible predisposition to malignant (cancerous) changes. More frequent health checks should be carried out.

Tumours and swelling
The sheath can be the site of skin tumours — melanomas being one of the most common examples.

Melanomas usually occur in grey horses over six years old. Check for sheath melanomas at least every three months, and take prompt action if required. Surgical removal or laser surgery is advised at an early stage.

Other sites where you may find melanomas, alerting you to check the sheath, are the salivary glands at the base of the ears, or under the tail and around the anus.

The outside of the sheath is a relatively common site for sarcoids. These skin cancers can vary from the occult sarcoid, which looks like an area of de-pigmented skin, to the more obvious verrucose or warty type. Your vet will advise you as to the best way of managing each individual sarcoid.

A common cause of sheath swelling is insect bites, as midges and flies are attracted to this region.

Gentle cleaning of any dried blood caused by bites is advisable, while cold compresses or hosing can help reduce swelling.

Severe swelling from insect bites may need vet treatment and possibly cortisone injections or antihistamines. Fly and midge control using repellents, appropriate rugs and stabling at the worst times of the day in summer can aid prevention.

Another, often overlooked, reason for sheath swelling is fat deposition, as overweight male horses often have large sheaths. An enlarged, fatty sheath in an aged gelding can be associated with Cushing’s syndrome.

Swelling can also be due to serious systemic (general body) disease such as hypoproteinemia, a loss of proteins from the body caused by inflammation or damage to the wall of the intestines.

This is usually caused by small redworms or intestinal ulceration, or is a possible side effect of non-steroidal anti-inflammatory agents such as phenylbutazone (bute).

Reduced proteins in the blood can lead to fluid leaking from the tissues and gathering along the horse’s belly and in the sheath, causing it to swell.

Paraphymosis or penile prolapse can be a complication of hypoproteinemia and result in massive swelling of the penis. The penis must be put into a special body sling to prevent further swelling while the background illness is treated.

Problems with the penis
Some horses like to urinate in private or do not protrude the penis, making early detection of problems difficult. Short daylight hours in winter and rugs can also obscure the view of this area.

Squamous cell carcinoma (SCC) is more common in geldings and older horses and presents on the penis as a nodule or surface ulceration. A possible link between SCC and poor sheath hygiene with the accumulation of smegma remains under investigation.

The surface of the penis may change in appearance or colour or develop an abnormal growth on the end or side. A preputial discharge, possibly foul smelling and with blood, may be the first thing you spot.

Biopsy of the mass may be needed to confirm the diagnosis. In most cases, surgical removal with a wide margin around the tumour area is the treatment of choice.

Depending on the size of the lesion and how far along the penis the tumour extends, partial or complete penis amputation may be considered.

SCC can be malignant and metastasize (spread) to the local lymph nodes or to other parts of the body.  If the disease is extensive in an older equine, euthanasia at an appropriate time may be the most humane option.

Horses can show different patterns of urination, especially in association with competition, racing or hunting, so owners and trainers need to get to know an individual so that abnormal changes can be detected.

Difficulty or increased frequency of urination (dysuria) and any blood in the urine or at the end of urination requires vet investigation. While obstruction of the urinary tract is uncommon in horses, calculi (stones) — frequently associated with increasing age in geldings — are the most common cause.

This article was first published in Horse & Hound magazine (4 September 2014)