Most veterinarians and breed associations advise that only the best animals should be kept for breeding purposes. Adequate facilities and training are usual prerequisites to correctly handling a stud. Some stallions can be worked and ridden like other horses, but most exhibit more aggressive behavior and can be unpredictable. Stallions are often kept by themselves because they tend to be dominant over mares and geldings, and fights often occur unless they are separated. This necessary separation is the most difficult thing for animals that normally live in herds.
Castration is one of the most common surgical procedures performed in equine medicine.
Castrating at an early age makes sense because young colts are easy to handle, the testicles are smaller and the incision can be sutured closed. That means less swelling and a resultantly good cosmetic appearance. Horses castrated in their weanling year do not develop some of the musculature and neck and facial features associated with stallions. These early geldings keep finer features, thinner necks and lighter muscle mass, though they can grow taller than they might if left entire. Many castrations are performed on colts between one and two years old, and due to the larger size of the testicles, the incisions must remain open.