Causes of chronic weight loss
Chronic weight loss can be multi factorial and a list of possible diagnoses can be
haunting to the owner. A methodical evaluation along with focusing on the most
common causes is the recommended approach to determining the inciting cause of
the weight loss.
Common causes of chronic weight loss in horses include reduced caloric intake,
inability to utilize nutrients, or increased exercise with more metabolic demands
(increasing work load). Careful monitoring of eating habits daily is a good way to
rule out caloric intake problems. If your horse seems to have a good appetite and
still continuously shows significant weight loss, the next approach is to evaluate
feeding management issues, such as quality and/or quantity of the feed offered.
Having hay tested for nutrients is one way to evaluate this. It is also important to
remember that horses belong to a social hierarchy and in some feeding situations
the horse that is lower in the social order may have difficulty getting all the calories
needed while getting chased away from the food source.
The next common cause of chronic weight loss is dentition problems. If the horse in
unable to chew efficiently or comfortably, his/her caloric intake may be decreased.
Having your horse’s teeth checked routinely will aid in ruling out dental issues as a
common cause of weight loss.
Decreased ability to utilize nutrients effectively results from conditions that alter
absorption or digestion of nutrients. Common examples of this include parasitism,
chronic diarrhea, and infiltrative disease altering absorption in the gastrointestinal
Increased metabolic demand, a cause of weight loss, also results from normal
conditions such as growth, exercise, pregnancy, and lactation, as well as illnesses.
Initial evaluation of the horse should be conducted by your veterinarian. A
thorough history from the owner is helpful in pointing the veterinarian in the right
direction. Information that is important includes de-worming protocol, feeding
environment, amount and type of feed including supplementation and medications.
A complete physical exam including an oral exam is helpful in ruling our your most
common problems. Blood work and a fecal parasite analysis are important tests
to have performed to obtain all information regarding overall health status of the
Routine blood work help recognize originators of weight loss and issues secondary
to poor body condition. A complete blood count (CBC) can determine if there is
evidence of infection or inflammation as can abnormalities found on physical exam.
Biochemistry parameters are used to assess liver and kidney function, altered
protein levels, muscle disorders, and electrolyte abnormalities.
If the initial tests do not appear abnormal, additional diagnostic tools are
recommended. The following are additional tests that are performed in no specific
order. These tests help analyze portions of the GI system that may be affected.
Abdominocentesis (sampling of abdominal fluid) and cytologic evaluation of the
sample can identify the health of the fluid within the abdomen and determine if
peritonitis (infection within the abdomen) or cancer is present. Rectal mucosal
biopsy samples can be analyzed by histopathology (looking at the architecture
of the tissue to further characterize infiltrative disease of the GI tract). Glucose
absorption tests can be performed to evaluate gastrointestinal absorption. A
veterinarian administers a specific quantity of glucose orally and tests blood
samples to identify the glucose levels over a period of time. Decreased absorption
is consistent with malabsorptive or infiltrative intestinal disease. Additional
blood testing can be done to further evaluate liver function, kidney function and to
diagnose metabolic disease. Vitamin E and selenium and other muscle tests may also
be considered when there is muscle wasting and increased muscle enzymes present
on the biochemistry panel.
If diagnostic tests and evaluations in the field fail to yield a diagnosis, more
extensive testing is recommended. Referral to a large animal veterinary practice
for advanced testing using gastroscopy, abdominal radiography, ultrasonography,
echocardiography, and organ biopsies for histopathology is recommended. An
attentive diagnostic approach to most chronic weight loss cases will reveal a cause,
although some cases will remain undiagnosed even after extensive testing.
If you have questions regarding weight loss or other medical problems in general
or affecting your horse, please discuss them with your veterinarian or with the
veterinarians at New England Equine Medical & Surgical Center.
Katy Raynor, DVM
Jacqueline Bartol, DVM, DACVIM