for breeding mares, greater certainty of what mares are bred when, less risk of escape or theft, and ease of access by humans. Some stallions are of such a temperament, or develop vicious behavior due to improper socialization or poor handling, that they must be confined and cannot be kept in a natural setting, either because they behave in a dangerous manner toward other horses, or because they are dangerous to humans when loose. The drawbacks to confinement vary with the details of the actual method used, but stallions kept out of a herd setting require a careful balance of nutrition and exercise for optimal health and fertility. Lack of exercise can be a serious concern; stallions without sufficient exercise may not only become fat, which may reduce both health and fertility, but also may become aggressive or develop stable vices due to pent-up energy. Some stallions within sight or sound of other horses may become aggressive or noisy, calling or challenging other horses. This sometimes is addressed by keeping stallions in complete isolation from other animals. However, complete isolation has significant drawbacks; stallions may develop additional behavior problems with aggression due to frustration and pent-up energy. As a general rule, a stallion that has been isolated from the time of weaning or sexual maturity will have a more difficult time adapting to a herd environment than one allowed to live close to other animals. However, as horses are instinctively social creatures, even stallions are believed to benefit from being allowed social interaction with other horses, though proper management and cautions are needed. Some managers attempt to compromise between the two methods by providing stallions daily turnout by themselves in a field where they can see, smell, and hear other horses. They may be stabled in a barn where there are bars or a grille between stalls where they can look out and see other animals. In some cases, a stallion may be kept with or next to a gelding or a nonhorse companion animal such as a goat, a gelded donkey, a cat, or other creature. Properly trained stallions can live and work close to mares and to one another. Examples include the Lipizzan stallions of the Spanish Riding School in Vienna, Austria, where the entire group of stallions live part-time in a bachelor herd as young colts, then are stabled, train, perform, and travel worldwide as adults with