Before puberty the testicles may be too small to be seen, but can be felt. Testosterone, the hormone responsible for male breeding behavior and some forms of aggression, diminishes to minimal levels within 48 hours of surgery. It is possible for geldings to exhibit stallion-like behavior, including breeding mares. If the horse is extremely aggressive, hormone tests may be indicated to determine whether or not a retained testicle is present. Most stallion-like behavior in the gelding is attributed to a small amount of testosterone secretion by the adrenal glands near the kidney.
Management usually involves separation from mares, if necessary, and sometimes hormone treatment.
Since the adrenal glands are necessary for life, they cannot be surgically altered.