Some horse owners feel that it is necessary to 'clean' a colt or gelding's prepuce (sheath) and penis on a fairly regular basis. While this may seem an innocent attempt to keep their horse 'clean', sheath washing is usually unnecessary and can result in the establishment of quite severe bacterial infection that can be very difficult to resolve.
What is normal?
In the relaxed, i.e., non-erect state, the horse's penis normally remains within its protective sheath where it is held in place by muscles. When these muscles relax and/or the penis fills with blood and becomes erect, it becomes exposed. At the tip of the penis (the glans) is the opening of the urethra. This is surrounded by a deep 'pocket', or fossa. Apart from the glans, that is covered by a thin sensitive membrane, the rest of the penis (shaft) is covered by smooth, supple, well-oiled skin, much of which is normally folded within the prepuce. Debris from the normal secretions of the skin glands and normally-dying cells from the surface of the skin within the sheath may accumulate in these folds and in the urethral fossa and sinus. This accumulation of waxy material is called 'smegma'. It may be black, grey or cream colored in normal horses and has a slightly greasy feel. It occasionally forms into bean-shaped lumps that lodge in the urethral fossa and sinus. Some horses produce very little smegma whereas others produce large quantities. In such horses, smegma can often be seen staining the opening of the sheath and on the inside of the thighs and hocks.
The penis and sheath have a permanent population of normal bacteria on their surface, just as all skin surfaces do. These bacteria do not cause disease; they undoubtedly help maintain the health of the skin and may help prevent infection by controlling 'unwelcome' bacteria. The urethral fossa and sinus, in particular, can harbor potential venereal disease producing bacteria (specifically Klebsiella pneumoniae, Pseudomonas aeruginosa and Taylorella equigenitalis). Infection with these organisms can cause venereal disease in mares following mating but rarely cause signs or symptoms of disease in the carrier stallion, who is usually infected by a carrier mare. When stallions become infected, these organisms may survive on the penile skin alongside of the 'normal' bacterial population and can then be very difficult to remove.
What harm can sheath cleaning do?
Although sheath washing sounds like a good idea and has been recommended by horsemen universally over the years as an important routine equine management procedure, it can have a detrimental effect if the normal 'ecological' balance of skin bacteria is disturbed. Washing the penis and sheath with strong detergent solutions can remove the natural skin oils, resulting in dry penile skin that cracks as it folds and unfolds, causing irritation and damage followed by inflammation and secondary infection. If this infection is caused by bacteria that are easy to treat, the problem may resolve spontaneously once washing with detergent has stopped. Local (creams or ointments) or systemic (by injection or by mouth) antibiotic treatment may be necessary.
Repeated washing with antiseptic, i.e., antibacterial washes or detergent solutions can result in alteration or removal of the normal penile skin bacterial population. This may result in colonization by unwelcome bacteria that are not normally present, either from the stable environment or following mating with a venereal disease carrier mare, and severe penile skin and sheath infections can result. The infection results in inflammation, swelling of local tissues and a profuse foul-smelling discharge that is much more unpleasant than smegma.
These infections can be extremely difficult to treat due to the resistant nature of some unwelcome bacteria. In such cases, prolonged treatment with specific systemic and topical antibiotics may be necessary, followed by a period of rest and then the application of a specially-prepared 'normal' penile skin bacterial broth culture to re-colonize the area. In some cases even this treatment may be unsuccessful and chronic infection may result in thickened cracked penile skin and extreme discomfort.
How should sheath cleaning be performed?
If your horse appears to have a healthy penis and sheath there is almost certainly no need to wash it at all. In horses that produce large amounts of smegma and appear uncomfortable, and in show horses or others where this would be considered unsightly, excess smegma can be wiped or rinsed away with warm clean water using simple soap that contains no antiseptics or detergents. A small amount of light mineral oil (such as baby oil) may help to loosen lumps and make excessive smegma easier to remove. It is important to be gentle and not abrade the skin and to rinse all trace of soap away. For healthy breeding stallions, rinsing the relaxing penis with warm clean water immediately on dismount is all that is required.
Edited by Kim McGurrin BSc DVM DVSc Diplomate ACVIM © Copyright 2010 Lifelearn Inc. Used and/or modified with permission under license.