Weight Loss in the Adult Horse

There are innumerable potential causes of weight loss, many of the more common of which can be identified by detailed consideration of the history and physical examination. If further investigations are required a systematic approach should first attempt to localize the problem to one or more body systems.

The four major mechanisms of weight loss are:

1. Reduced intake: inappropriate feeding, unable to obtain feed, competition for feed, dental disorders, dysphagia.
2. Reduced digestion, absorption or assimilation of nutrients: dental disorders, malabsorption syndromes, infiltrative or inflammatory bowel disease (IBD), liver disease.
3. Increased losses: parasites, protein loosing enteropathy, nephropathy, or protein sequestration to body cavity i.e. peritonitis or pleuritis.
4. Increased requirements: sepsis, neoplasia, other systemic disease, pregnancy, lactation.

History

Clinical Approach
In addition to general information on the duration and nature of presenting signs, the history should focus on establishing whether the horse is being fed adequately and is able to swallow the feed it is offered and the anthelminitic regimen should be evaluated critically.

Physical Examination
Clearly it is important to first establish that the horse is truly under-weight and the physical examination should be careful and detailed as often, subtle clinical abnormalities may be important in weight loss cases. It can be useful to have the owner make a daily record of the rectal temperature as this may be more informative than a single measurement. Several of the infiltrative bowel disorders can have concurrent skin lesions and even fairly mild skin lesions can be important. A transrectal examination is mandatory in persistent weight loss cases and a full dental examination, under sedation and using a gag, should be performed before undertaking further investigations.

Haematology and Blood Biochemistry
An initial haematology and biochemistry screen may reveal evidence of infection, liver disease or renal disease and possibly provide supporting evidence of gastrointestinal (GI) disease. Biochemical abnormalities are not consistent in GI disease: low serum protein concentrations are most likely to be due to protein-loosing enteropathy although protein loss from the kidneys or sequestration into a body cavity is also possible. Intestinal alkaline phosphatase is sometimes increased but many cases of GI disease will have unremarkable findings.  [...]