Weight Loss

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Also Known As

Failure to thrive, Underweight


Weight loss in a horse can be a complex problem to solve. Certain situations in the life of the horse, such as pregnancy, lactation, breeding season, high performance levels during racing season, and other events lead to natural weight loss.

Once circumstances change, the horse usually goes back to, essentially, the same weight as before.

The weight loss that truly should concern horse owners, handlers, and veterinarians is weight loss, either subtle or dramatic, that may be related to career-ending or life-threatening diseases and conditions.


  • Horse has visible ribs, a ridge down its back, and a prominent tail head
  • Withers, shoulders, and neck are accentuated
  • Horse is emaciated, with prominent bone projections through skin
  • No fatty tissue can be felt
  • Lethargy and dullness affect behavior
  • Exercise intolerance is noticeable
  • Depression is apparent


Equine weight loss has many causes. Those that most concern owners, handlers, and veterinarians usually relate to diseases, both primary and secondary, parasites, the condition of teeth, mouth and gums, nutritional deficiencies, metabolic disturbances, malabsorption problems, chronic, painful conditions, chronic infections, neoplasia, aging processes, and stereotypies or vices.

Some horses develop anorexia, which is loss of appetite or lack of desire for food, usually as a secondary condition related to a primary disease. Acute anorexia results in a dramatic weight loss, whereas partial anorexia leads to subtle weight loss over a longer time period.

Conditions that cause a horse to lose its appetite include trauma, sepsis, parasitism, injury, neoplasia, organ failure, inadequate feed quality or quantity, and/or deficiency of essential nutrients, such as copper, Vitamin B-12, or Vitamin A.

Horses that have to compete for feed may appear to be anorexic, but, in reality, cannot eat quickly enough or compete with other horses for sufficient feed to keep them well-nourished.

Dental and mouth problems may also lead to weight loss. Abnormal dental wear, leading to development of sharp points on teeth that cause abrasions and make chewing painful, will cause a horse to stop eating sufficient calories to maintain weight. Problems with swallowing caused by tumors or disease also lead to weight loss.

Chronic, painful conditions such as arthritis, chronic laminitis, non-healing wounds, invasive tumors, or other conditions that reduce the horse's mobility, desire for food, and ability to graze will lead to weight loss, as will chronic infections such as EIA, internal abscesses, chronic bacterial infections, and chronic obstructive pulmonary disease.

Tumors and cancers often cause reduced intake of feed as a result of pain from physical obstruction, maldigestion, or malabsorption. Large tumors or cancers make significant metabolic demands on a horse's system. Lymphosarcoma is the most common internal cancer in horses and often affects the liver, spleen, and lungs, leading to loss of weight.

Chronic diarrhea and parasitism of the large intestine, granulomatous enteritis, and ulcerative lesions lead to loss of body fluids, competition for nutrients in the gastrointestinal tract, inflammation, micronutrient deficiencies, and loss of appetite and weight in stricken horses, with serious consequences if not diagnosed and treated.

Another cause of serious weight loss in horses relates to insufficient feed, poor quality feed, or the wrong combination of feed for the horse's energy or nutrient requirements. In addition, the energy density of feed may not be adequate as work or performance demands increase.

Some stereotypies cause a horse to engage in behaviors that either demand more energy than feed intake meets or cause the horse's appetite to diminish, as a form of anorexia develops.


Much of the prevention of weight loss is based on sound horse management, quick and accurate diagnosis of diseases and conditions, careful attention to the demands for nutritional intake based on exercise and performance levels, and knowledge of each particular horse's ongoing physical condition.

Some horses are thin by nature, so it is mainly when a horse loses weight combined with a loss of condition that owners and handlers should be concerned.


First and foremost, treatment of weight loss depends on accurate diagnosis and treatment of the disease or condition that is causing the horse to lose weight.

In the case of nutritional deficiencies, evaluation by a veterinarian, with additions and changes to the horse's diet to increase nutritional value and make sure the horse is getting all the nutrients required by the exercise/work level and age of the horse, usually works well.

A good parasite control program should be in place to keep the horse healthy. Horses should be examined on a regular basis to determine dental health and correct any problems.

If the horse has a tendency to be thin in spite of being healthy, switching to a commercial feed or putting the horse on pasture containing an abundance of high-quality forage will help. Cereal grain may be added to the daily ration to help the horse maintain proper weight.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.