A gelding is a castrated male horse or other equine, such as a pony, donkey or a mule. The term is also used with certain other animals and livestock, such as domesticated camels. By comparison, the equivalent term for a castrated male bull would be ox (or oxen), or a wether for rams and billy goats.
Castration (in addition to the elimination of hormonally-driven behavior associated with a stallion) allows a male animal to be more calm, better-behaved, less sexually-aggressive, and more responsive to training efforts. Additionally, it is known for making the animal quieter, gentler and generally more suitable as an everyday working animal, or even as a pet (in the case of companion animals). The gerund and participle "gelding" and the infinitive "to geld" refer to the castration procedure itself.
The verb "to geld" comes from the Old Norse gelda, from the adjective geldr 'barren'. The noun "gelding" is from the Old Norse geldingr.
The Scythians are thought to have been among the first to geld their horses, as they valued war horses that were quiet and less defensive, as well as easier to keep in groups and less likely to be territorial, without the temptation of reproductive/mating urges. Aristotle is said to have mentioned gelding as early as 350 BC.
Horse behavior and Horse breeding
A male horse is often gelded to make him better-behaved and easier to control. Gelding can also remove lower-quality animals from the gene pool.
To allow only the finest animals to breed on, while preserving adequate genetic diversity, only a small percentage of all male horses should remain stallions. Mainstream sources place the percentage of stallions that should be kept as breeding stock at about 10%, while an extreme view states that only 0.5% of all males should be bred. In wild herds, the 10% ratio is largely maintained naturally, as a single dominant stallion usually protects and breeds with a herd which is seldom larger than 10 or 12 mares, though he may permit a less dominant junior stallion to live at the fringes of the herd.