Overly fat or obese horses have become the number one nutritional problem in horses kept in affluent societies and continues to grow toward the overall number one health problem of horse owners. We define obesity not by any particular weight of a horse but by body condition score which is a rough measure of how much fat the horses is carrying. Horses are healthiest when they are carrying a Henneke body condition score of between a 5 and a 6. This will vary a bit depending of the type work a horse does ...more on body condition scoring.

Horses tend to eat the amount of feed needed to meet its energy needs but also has some amount of chewing time requirements and fullness feeling requirements that control their desire to feed. There are several reasons horses under modern management regimens may become obese:

• If the feed is very palatable or has high energy density horses easily eat more than required to meet their energy needs.
• The amount of exercise low so caloric needs are low.
• The horses metabolism is unusually energy conserving. Though this is related to exercise it is also a factor unto itself with a almost 300% range in energy requirements in similar horses.

Even mature (stemmy) cultivated pasture and hays represent much better than average that occurs naturally and simply restricting access to pasture may not be enough. With restricted access to forages horses speed up their rate of consumption and can consume a whole days forage in as little as 6 hours as opposed to the more leisurely 16 hours when offered free choice.

If a horse chronically takes in more energy than he expends, weight gain occurs and if it continues the horse becomes obese with a body condition score greater than a 7. There are serious medical and psychological effects from chronic excessive feeding. This article discusses the causes and health consequences of obesity and how to go about correcting it while keeping your horse happy.

Simply put horses are obese because we feed excessively rich feeds in excessive amounts and we ride our horses to little. It is important to understand there are both important physiological and psychological effects from excessive feeding that lead to medical problems:

• increase weight
• excess body heat
• while in positive energy balance the horse may be excessively high spirited as demonstrated by a tendency to buck, shy, and run away. Once obese the horse becomes lethargic.
• in growing horses the increased growth rate and possibly increased occurrence of developmental orthopedic diseases

Over time excessive feeding the result is obesity with the following medical effects:

• decreased performance ability
• a decreased ability to cool
• increased sweating with physical activity.
• increases respiratory difficulties
• increased strain on the laminae of the hooves, predisposing to founder

Decreased performance is due to the increased weight the horse has to carry and to a decreased ability to cool the body because excess subcutaneous fat provides increased insulation. An obese horse in moderate to hot conditions with twenty minutes at a rapid trotting speed produces sufficient heat to cause hyperthermia-induced fatigue and even death. Respiratory difficulties probably also contribute to decreased physical activity and performance in the overweight horse. These effects are reversed by weight loss.

A condition that shadows the human condition of type 2 diabetes is now recognized in horses. Called Equine Metabolic Syndrome it is characterized by obesity and founder and may be the result of feeding excessive energy. These horses are hard to get weight off of and the founder difficult to manage, ...more.