Malnutrition is not the same as under-nutrition. Malnutrition is underfeeding, overfeeding or feeding of any nutrient in the wrong proportion. Under-nutrition, as described here, means underfeeding of energy or protein.

Under-nutrition is the most common cause of weight loss in the horse and results when an otherwise healthy horse receives fewer calories than it needs to maintain ideal weight. The amount of calories required for a particular horse to maintain weight depends on many factors including breed, age, individual genetic factors, stage of development, exercise (work) level, among many others.

Under-nutrition could mean that the horse is eating too little of a nutritious feed, eating feed that is of poor nutritional value, or both.

A common scenario is individual horses within a group that do not get as much feed as needed, because they are excluded from feed by more dominant individuals.

The most common sign of under-nutrition is weight loss, but undernourished horses often have a poor hair coat and hoof quality. Undernourished horses are also more likely to acquire infections and other illnesses.

Direct signs of vitamin and mineral deficiency may be also be seen, depending on the nutrients lacking.

Your vet will try to rule out other causes of these signs using examination and diagnostics, and carefully assess your feeding and management program. In cases of under-nutrition, accompanied by no other underlying cause, increasing the quality and/or amount of feed should result in the necessary weight gain and improvement.