Cryptorchidism in the Male Horse

Nov 14, 2011
Chris Thomas

Stallion's can Require Special Management - C. Thomas

Commonly termed a rig, the cryptorchid has one or no descended testes. This can result in the appearance of a gelding, but stallion qualities.

When the foal is developing inside the mare, the testes of the colt live for a time in the abdomen. Later in the pregnancy, they travel a pathway through the inguinal ring and end up outside the horse’s body. An inconsistency in this process may result in one or both testes not descending and the horse being termed a cryptorchid.

Issues with the Cryptorchid

Although externally the horse may look like a gelding, he isn’t. This can result in the male horse having characteristics typical of a stallion. He will still have the effects of testosterone that result in:

a cresty neck
extra muscle
a raised awareness of other horses, especially mares

For a horse where neither of the testes has descended, the possibility of utilising him as a stallion is limited. The testes sit outside the body just below body temperature normally. The sperm are produced and stored in the testes. A horse that has its testes contained within the abdomen probably won’t be producing viable sperm for reproduction, due to the raised temperature negatively affecting sperm.

The rig with one descended testicle may still be a breeding prospect, although certain stud books will not allow registration of particular breeds if the horse is a cryptorchid. It is believed by some that there is a hereditary link between cryptorchids, and that not allowing such stallions to breed will help lessen the likelihood of this being passed on genetically.

In either case, surgery to remove the abdominal testes will assist in alleviating stallion like behaviour. For the rig that isn’t to be used for breeding, castration is worth considering.

Management of the gelding can be a lot more straightforward, generally resulting in a horse that is easier to handle, can be put out with any other class of horses and won’t be easily distracted by mares. Having the horse gelded can therefore save on having to house him in a separate paddock or yard and make it easier for any staff to handle the horse. For the male horse that won’t be used to breed and where height is desirable, it has also been suggested that early castration allows energy to be put into height, rather than increased muscle mass and tone.

A cryptorchid is worth inspecting to determine whether one or both testes are affected. A vet can assist in this process. Future plans with the horse will help to determine the best course of action.