The penis of a male horse is contained in a loose double fold of skin called the sheath. Muscles keep the penis retracted within the sheath except when the horse stands to urinate or becomes sexually excited.
A sheath with a bumpy mass may be the accumulation of smegma, a pasty substance that lubricates and protects the sheath. However, a sheath with multiple lumps and growths needs further evaluation by the veterinarian.
Length
The length of a horse penis when erect is on average 24-32 inches. This is comparable to other mammals, including lions and humans. The long penis is essential to sexual reproduction in male horses. It allows sperm to travel deep into female horses’ extremely large vaginas.
The urethra protrudes into a distinctive central fossa (fossa glandis) at the free end of the corona. Dirt, sweat and secretions will often accumulate in this groove (Fig. 4.9). This accumulation of debris is commonly known as the “bean.”
During ejaculation, the sheath opens at the glans and the urethra ejects into the mare’s uterus through the cervical canal. The ejaculate may also be discharged through the anal orifices during copulation. The ejaculate contains only a small number of spermatozoa and does not stimulate further production in the epididymis.
The sheath is a difficult area to examine for lesions and abnormalities. Some stallions are reluctant to be examined in this area and may cow kick or kick backwards. Therefore, this region should be carefully manipulated to avoid injuries to the examiner and the animal. During routine vaccinations, the veterinarian can carefully check for sheath conditions such as summer sores and bacterial infections. Also, it is important to regularly observe the penis and sheath for changes in skin texture and size. This will allow you to recognize abnormalities early and take appropriate action.
Width
The glans penis is shaped like a mushroom with a distinctive central fossa (urethral fossa). The urethra passes through this opening and exits from the sheath. The sheath itself may be a little larger than other parts of the genital tract due to the smegma it carries, which lubricates and protects the glans penis and the sheath.
Testosterone plays a critical role in the growth of the penis and other male reproductive organs, especially during sexual activity. It is also the hormone that causes a man to have an erection. The sheath is a thick and viscous substance that helps to carry the smegma. It also provides a protective layer against irritation and infection.
Stallions are particularly prone to trauma and injuries to the sheath and penis, especially when they are covering mares. Consequently, it is important to regularly examine the penis and sheath for signs of abnormality. This examination can be done easily while grooming or saddling your horse, or by simply observing the sheath as the horse stands to urinate.
A large swollen sheath that does not drain normally should be examined by a veterinarian immediately. A swollen sheath is often a sign of disease, and squamous cell carcinoma (SCC) is the most common lesion that can affect the penis and sheath. SCC is more likely to develop on light-coloured horses, including Appaloosas, greys and palominos, as well as older horses.
Thickness
A horse’s penis is incredibly thick compared to other animals, including lions. The thickness is a key reason why horses are able to quickly retract their gonads (the term used for the horse’s penis and sheath) when stressed or threatened. This allows the animal to hide its genitals from predators and also protect it from heat or cold.
The shape of the equine penile glans is similar to that of a mushroom, with the urethra protruding into a distinctive central fossa at its free end. This increases in size during erection, allowing the mare’s cervical canal to dilate and deposition of the spermatozoa directly into the uterus in copulation.
At birth, each testis is very small and weighs 5 to 10 grams. A slight growth occurs between the age of 11 and 16 months, but the testes don’t reach full maturity until a stallion is 12 to 13 years old.
As the most important part of the reproductive system, the gonads are prone to disease. The most common neoplasm that affects the equine glans, prepuce and sheath is squamous cell carcinoma. Squamous cell cancer is most likely to occur in light-coloured horses, including Appaloosas, greys and palominos. It is not uncommon for a gelding or stallion to develop pink tissue on his sheath and penis, so if you notice anything unusual in this area it is important that you get the problem checked out by your veterinarian.
Weight
A horse’s penis can be as much as 36 inches long when erect. It’s not an unusual size, but some stallions have much longer ones than others.
The horse’s penis and sheath are lubricated by sebaceous glands within the sheath. The lubrication mixes with sweat, dirt and natural bacteria and forms a thick waxy substance called smegma. This smegma accumulates in the urethral fossa, which is the opening at the end of the penis (fig. 4.9). As it builds up, it can block the free end of the penis or cause pain.
As a result, regular visual examination of the penis and sheath should become a part of your horse’s care routine. This can be done by exteriorising the penis while he is urinating or extremely relaxed and by running your hand over the sheath to feel for a smegma bean.
If a smegma bean is present, it needs to be manually removed as it can get larger and block the penis. Cleaning the sheath and penis is also important as it can reduce gravitational oedema that can lead to trauma and paraphimosis. It is possible to manage many cases of paraphimosis and avoid the need for phallopexy or phallectomy with good sheath care. This includes examining the sheath and penis on a daily basis, cleaning as needed and regular massage (3 to 4 times per day). A veterinarian should direct early treatment for paraphimosis and priapism.
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