A colt can be castrated at any age as long as both testicles are descended into the scrotum. The testicles are usually in the scrotum at birth; however, it is not unusual for one or both to remain in the body cavity until ten months of age. Occasionally the testicles are not completely descended until the twelfth month of age. Many farms will castrate during either the winter or spring months prior to the colt’s first year of age. Insects are less of a problem at this time of year, and cooler weather should help prevent swelling.