Weight Loss in Horses

What Is 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).

Weight loss is a problem most commonly seen in older horses, but can happen at any age. Some breeds, like Arabians and Thoroughbreds, are more prone to this medical condition.

Weight loss in horses is often a subtle and a symptom of an underlying disease. A thorough work-up by a veterinarian may be necessary to find the source of the problem.

Signs a Horse is Losing Weight

An underweight horse may have visible ribs, protruding hip bones or shoulders, and may appear sunken in along their topline. They may also develop a rough, dull hair coat and have brittle or weak hooves.

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

• Tailhead

• Ribs

• 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 to see if they’re at an appropriate weight.

Depending on the root cause of the weight loss, you may notice other symptoms that accompany weight loss in horses, such as:

• Poor appetite

• Quidding (dropping feed)

• Recurrent episodes of colic

• Lameness

• Decreased energy levels

• Diarrhea

If the horse in question is a part of a herd, it is important to observe the herd dynamics. An underweight horse may be at the lower end of the community hierarchy. Your horse may be having their food stolen by other horses, so be sure to watch herd behavior at feeding time. It’s also helpful to note if a single horse, or multiple in the herd are dealing with weight loss.

Causes of Weight Loss in Horses

Conditions that may lead to weight loss in horses include:

• Poor nutrition: quality, amount, access

• Dental issues

• Parasites

• Metabolic disease such as Cushing’s disease

• Neoplasia (cancer)

• Poor gastrointestinal absorption of nutrients, which can occur with senior horses or due to parasites or sand colic

• Infectious diseases such as bacterial digestive infections, internal abscesses, equine infectious anemia, Lyme disease, EPM, and many others

Diagnosing Weight Loss in Horses

Evaluating a horse for weight loss should start with a thorough history and clinical exam, with a rectal palpation to feel for potential internal masses and sand, and a fecal analysis.

Once the common conditions that lead to weight loss are ruled out, a systematic evaluation of less-common conditions should be pursued. This will require further diagnostics tests, such as:

• Complete blood work 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 such as abscesses in the thoracic (chest) 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.

How To Help Your Horse Gain Weight

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

Ensure Proper Nutrition

Ensuring your horse eats appropriate nutrition is an important initial step.

Forage is the ideal source of calories and energy for horses. Allowing your horse access to pasture or hay as much as possible is best. If increased volume of hay is not enough to correct weight loss in a malnourished horse, 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 can be added to the diet, such as:

• Rice bran oil

• Flaxseed oil

• Vegetable oil

• Dried granular fats

When making diet changes, always proceed gradually, ideally over a two to three week period to allow your horse’s digestive system to acclimate to the changes.

Watch for Dental and Digestive Issues

Some older horses no longer have the teeth quality required to chew hard forage. A horse with dental issues may drop feed or not eat their food due to pain.

Changes in a horse’s digestive tract can make it difficult for them to obtain the nutrients they need from forage. Signs of digestive upset may include colic, not eating, or changes in bowel movements.

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.

Treat Underlying Disease

Weight loss in horses with 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, the disease 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 such as dexamethasone or prednisone.

Monitoring Your Horse’s Weight

It is a good practice to routinely monitor your horse’s weight. Three ways to monitor your horse’s weight are:

1. Keeping tabs on their body condition score

2. Frequently tracking their weight through tape measurement

3. Calculating their 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.

Prevention of Weight Loss in Horses

An important 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 in horses is usually secondary to an underlying condition, it may sometimes lead to other conditions like:

• Behavioral changes (food aggression)

• Musculoskeletal problems

• Poor performance due to lack of energy

• Infertility