Weight Loss in Horses

Weight loss, or ill-thrift, is a common problem in horses. Weight loss, by definition, is the reduction of total body mass. This reduction can be in the form of loss of fluid, fat, and/or lean body mass (which is comprised of muscle, bone, and connective tissue). It is a problem most commonly seen in older horses, but can be present at any age. Some breeds, like Arabians and Thoroughbreds, are more prone to this medical condition. Weight loss is often a subtle and subclinical symptom of an underlying disease. A thorough work-up by a veterinarian may be necessary to find the source of the problem.

Symptoms of Weight Loss in Horses

When determining if a horse is underweight, there are six main areas of the body to evaluate: along the neck, along the withers, the crease down the back, the tailhead, ribs, and behind the shoulder. These areas should be covered with a moderate amount of fleshy tissue and no bony sections should be noticeable. This evaluation will determine your horse’s body condition score.

Depending on the root cause of the weight loss, you may notice other symptoms that accompany ill-thrift, such as a poor appetite, quidding (dropping feed), recurrent episodes of colic, lameness, or diarrhea.

If the horse in question is a part of a herd, it is important to observe the herd dynamics. Is the underweight horse at the lower end of the community hierarchy? Are multiple horses underweight or just one individual? Your horse may be having their food stolen by other horses, so be sure to watch herd behavior at feeding time.

Causes of Weight Loss in Horses

Conditions that may lead to weight loss in horses include:

• Poor nutrition: quality, amount, access

• Dental disease

• Parasitism

• Metabolic disease

• Neoplasia (cancer)

• Infectious diseases

How Veterinarians Diagnose Weight Loss in Horses

Evaluating a horse for weight loss should start with a thorough history and clinical exam, with a rectal palpation and a fecal analysis. Once the common conditions that lead to weight loss are addressed, a systematic evaluation of less-common conditions should be pursued. This will require further diagnostics tests.

• Complete bloodwork and a urinalysis will help to determine if specific organ dysfunction is present, like kidney and liver disease, as well as chronic infection or inflammation.

• Specific blood tests that look for endocrine disorders, like Cushing’s disease or hyperthyroidism can be performed.

• Advanced imaging may be needed to diagnose the source of weight loss.

  • Ultrasound can be used to detect abnormal structures in the thoracic and abdominal cavities.

  • Endoscopy can be used to evaluate the stomach for disease like cancer or ulcers and to check the guttural pouches for infection.

• Tissue samples (biopsies) may be necessary for definitive diagnosis of some conditions, including some bowel diseases and cancers.

Treatment of Weight Loss in Horses

Treatment of weight loss varies significantly and will be determined by the cause of the weight loss.

Ensuring your horse eats appropriate nutrition is an important initial step. Forage is the ideal source of calories and energy for horses, therefore allowing access to pasture or hay as much as possible is ideal. If increased volume of hay is not enough to correct weight loss, a hay that is higher in calories and protein, like alfalfa hay or cubes, should be added to the diet. Adding a grain that is high in protein and fat to the diet will also be beneficial. If this is still inadequate to prevent or reverse weight loss, a high fat supplement like rice bran, flax seed, vegetable oil, or dried granular fats can be added to the diet. When making diet changes, always proceed gradually, ideally over a 2-3 week period to allow your horse’s digestive system to acclimate to the changes.

Some older horses no longer have the teeth quality required to chew hard forage. This, along with changes in their digestive tract can make it difficult for them to obtain the nutrients they need from forage. In these cases, they should be fed a complete feed which contains 100% of the horse’s fiber needs and is fed in larger amounts than regular grain.

Weight loss in horses with Pituitary Pars Intermedia Dysfunction, commonly referred to as Cushing’s disease, is due to a breakdown of muscle tissue. This specific form of weight loss requires special attention to diet (such as limiting carbohydrates) and exercise. Horses may also require medications like Pergolide.

If an infectious or inflammatory disease is found to be the cause of weight loss, it will need to be treated accordingly. Abscesses that are caused by infections with Corynebacterium or Streptococcus equi, may need to be surgically removed and followed up with antibiotic therapy. Some inflammatory diseases may be treated with steroids.

Recovery and Management of Weight Loss in Horses

It is a good practice to routinely monitor your horse’s weight. Three ways to monitor your horse’s weight are 1) body condition scoring 2) weight tape and 3) calculate a body weight equation. No matter which method you use, it is important to be consistent and perform the measurements the same way each time.

A good equation to use to monitor your horse’s weight is:

(Weight=(Heart girth (in) * Heart girth (in) * Length (in))

The length is the distance from the point of the shoulder to the point of the rump, and the girth is the circumference of the horse at the base of the withers, down the belly just behind the elbow and back around.

Another preventative measure of weight loss includes a routine parasite control program prescribed by your veterinarian and based on fecal egg counts. Sometimes, eggs may not be found in fecal material. In cases of tapeworms and encysted small strongyle larvae, deworming may be recommended despite not detecting parasite eggs from a fecal test. Additionally, routine dental exams and teeth floating will help make sure dental issues are not causing weight loss.

Though weight loss is usually secondary to an underlying condition, it may sometimes lead to behavioral changes (food aggression), musculoskeletal problems, poor performance due to lack of energy, and infertility.