Many horses are overweight, but the health significance of this condition in horses is unknown. In other species, various medical problems are associated with obesity. Fortunately most obesity-related diseases are not commonly diagnosed in horses. Obese horses do seem to be less exercise- and heat-tolerant, and more prone to founder, than are horses of normal weight. Obesity also will increase the risks of surgery if it becomes necessary.
Although horses may become obese for a variety of reasons, the most common one seems to be lack of attention to the animal’s body condition, combined with access to large quantities of palatable feed, and inadequate exercise. Inexperienced horse owners often mistakenly believe that their animals should receive a fixed amount of food daily, regardless of the animal’s environment or level of exercise. Horses are more appropriately fed by adjusting intake to maintain the animal’s body condition at approximately 4 to 6, depending on one’s personal preference.
Inactive adult horses often are fed a variety of concentrated feeds and treats in addition to their usual roughage ration. These animals often need little more than access to fresh water, good quality grass hay, and an appropriately formulated trace-mineralized salt. Additional feed should be provided at the expense of a portion of this diet rather than in addition to it. Moreover, if highly palatable grains or concentrates are provided with relatively unpalatable forages, horses may consume them instead of the forage.
In other animal species, obesity is notoriously difficult to treat, often because it requires change of deeply entrenched habits and beliefs about diet and feeding practices. Obesity is a problem that is more easily prevented by feeding "to the eye of the master" rather than the fullness of the hayrack or grain bucket, and by avoiding a relationship with pet horses based largely on provision of large quantities of food treats and rewards in addition to the animal’s usual diet.