By Larry R. Bramlage, DVM, MS

Castration is normally performed on colts to make them more tractable and easier to handle. When the horse has minimal breeding value, the procedure normally takes place once the horse is skeletally mature. In horses with potential breeding value, the decision to castrate is delayed to determine if the horse has enough athletic ability to make it attractive as a future sire. If the horse is not a potential sire, castration increases the longevity of its race career by making the horse easier to train. The mature, intact male horse becomes progressively more difficult to train and more aggressive as it gets older.

In some horses, the timing of the castration procedure is accelerated because they will have one testicle or sometimes both testicles partially undescended, which leaves the testicle in the flank of the horse between the leg and the abdomen. Sometimes this causes discomfort during training. If the horse has one testicle normally descended and one retained or undescended, the proper medical term is “cryptorchid” or the horseman’s term is “ridgling.” Non-descended testicles have much-reduced fertility or are sterile, as their retention in the inguinal canal makes them ineffective at producing sperm because of the increased temperature exposure of being adjacent to the body wall. In horses with high breeding potential, the non-descended testicle may be removed and the normal testicle will be left in place. This horse is called a “monorchid.” Monorchids can be fertile stallions. In horses whose pedigree does not indicate that they are likely to be a stallion, a unilateral cryptorchid is often castrated on both sides, normal and abnormal, during the same surgical procedure to facilitate the horse’s race career. 

The castration of a horse, once it is decided that it will not be a stallion, makes them much more tractable in training and a much more effective athlete. Many of the famous geldings of the past were totally ineffective racehorses as intact males and became stars once gelded.