From full-bodied Drafts to stream-lined Thoroughbreds, horses vary greatly in size and appearance. However, it is important to maintain all horses at an ideal body weight. When horses lose weight, it is easy to jump to the conclusion that a very serious problem is causing the weight loss. Fortunately, there are many simple, common causes that can explain a drop in body condition. A horse will lose weight when the calories that they are burning exceed the calories that they are eating.
There are many common causes of weight loss in horses. One is abnormal dentition. If a horse is unable to chew and grind its food due to a dental problem, the horse will not meet its caloric needs which will result in weight loss. Another common cause is parasitism by gastrointestinal parasites. If the horse is not dewormed using an appropriate deworming protocol, weight loss can result from an increased parasite burden. Other common causes include an inadequate diet, lack of fresh water, and competition for food or water with other horses. An inadequate diet includes situations where the diet lacks sufficient calories for the energy requirements of the horse or the type of diet is not appropriate for the particular horse. Competition for resources among a group of horses can be very subtle. Even minor changes in herd dynamics can lead to a horse not getting the food and water it requires to maintain its weight.
In addition to the common causes discussed previously, there are uncommon causes of weight loss in horses. These causes should only be considered after the common causes have been ruled out as the cause of the weight loss. These include an underlying chronic disease (for example recurrent airway obstruction or “heaves”), cancer, inflammatory disease of the gastrointestinal tract, infectious disease of the gastrointestinal tract especially in younger horses, and malabsorptive disorders.
If a horse seems to be losing weight, it should be examined by a veterinarian. The veterinarian will begin with a detailed history focusing on the common causes of weight loss for horses. This will include details such as what the horse eats, how often it is fed, where it is fed, whether it is housed in a group or alone, dental history, and deworming history. The veterinarian will then perform a thorough physical exam on the horse. The horse’s teeth should be examined and a fecal sample should be checked for internal parasites. These tests are focused on the common causes of weight loss in horses. If the cause of the weight loss cannot be determined through this information, additional tests can be pursued. These include bloodwork, a rectal exam, abdominal ultrasound, abdominocentesis (taking a sample of abdominal fluid), and glucose absorption tests. These tests will provide further information about the horse’s overall health, organ function, and abnormalities of the gastrointestinal tract. These tests will diagnose more uncommon causes of weight loss.
Initial treatments for weight loss usually begin with simple management changes for the horse to encourage weight gain. These include an appropriate diet for the horse. Factors to consider include age, intensity of exercise, pregnancy, lactation, and climate. This might include changing the type of feed, how much is fed, and how often feed is offered. If competition seems to be deterring the horse from eating or drinking, a change in housing might be necessary. The horse might need to be separated from the herd at feeding times or stalled individually to decrease competition and stress. A reduction in workload might be necessary for a short amount of time until the horse returns to an appropriate body condition. Routine dentistry and deworming protocols are recommended. A specific test (fecal egg count reduction test) can be used to determine if parasite resistance has developed to specific dewormers. This can aid in developing an appropriate deworming protocol for the horse. Body condition and weight should be monitored closely after these changes have been made. By instituting these treatments, the balance between calorie intake and expenditure will be balanced leading to a healthy, happy horse!