The sheath is a large fold of skin which protects the penis when it is not extruded for urination or breeding.
A wax-like substance called smegma is produced by the inside of the sheath to help maintain healthy skin in this area and to make it easier for the penis to be withdrawn. The amount of smegma produced by an individual varies greatly, and it can be moist and sticky, or dry and flakey. Smegma can occasionally build up, leading to discomfort, swelling or infection. This is more common in winter, and some horses will need their sheaths gently cleaning from time to time, but it is important not to over clean it. A horse’s entire skin has natural bacteria living on it, and the sheath is no exception. You must avoid disrupting these normal bacteria, as their removal will allow fungal overgrowth. A cursory wash with luke warm water should be all that required. Proprietary sheath cleaners are also available. Do not be tempted to use any antiseptic, such as Hibiscrub, as these will remove the natural bacteria. The sheath can be safely cleaned standing next to the horse’s ribs and gently wiping inside the sheath with a warm wet sponge. If he resents this, a little KY Jelly smeared on the inside will loosen smegma flakes. Occasionally, a solid build-up of smegma occurs in the urethral fossa, a small cavity in the tip of the penis. This is known as a “bean”, and might be painful or even cause difficulty urinating. Sometimes sedation is necessary to allow its removal. Other problems that can occur within the sheath include a bacterial or fungal infection, or less commonly melanomas or other tumours of the penis or sheath.
Infected sheaths are hot and painful, very swollen and sometimes with visible pus build-up. Tumours are more common in the older horses. Older geldings frequently have mildly swollen sheaths in winter as they move around less and circulation in the sheath becomes poorer in the cold weather. If a horse is overweight, fat can be stored in the sheath, making it appear swollen.
Call us for phone advice or an appointment if you have any concerns about your horse’s sheath.