Horse Side Vet Guide ®

Equine Health Resource

Weight Loss, Thin, Losing Weight

Code Orange - Call Your Vet at Their First Available Office Hours

Code Yellow - Contact Your Vet at Your Convenience for an Appointment

Code Orange - Call Your Vet at Their First Available Office Hours

  • If this problem seems severe and has come on suddenly.

Code Yellow - Contact Your Vet at Your Convenience for an Appointment

  • If you consider this a chronic and relatively mild problem that is not changing rapidly.
  • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.

Weight loss in horses can result from a few causes. A primary consideration is whether a horse’s energy expenditure exceeds their nutritional intake- simply not enough nutrition. Weight loss is commonly seen in an individual horse that is fed in a group. In this case, a dominant horse prevents another from eating their full ration. Dental issues can reduce a horse’s ability to properly process feed. Internal parasitism, the presence of intestinal worms can reduce efficiency of digestion and utilization of nutrients.

Older horses tend to be hard keepers due to a combination of dental issues and a reduced ability to absorb and utilize nutrients. Other somewhat less common causes include chronic diseases of many types: endocrine disease like PPID, cancer, chronic respiratory issues and especially chronic pain.


Know the common causes of weight loss and try to determine whether any of them may be affecting your horse. Especially consider your feeding program and whether the horse may not be getting access to enough feed. Assess your horse’s general health using the Whole Horse Exam (WHE), and share your findings and concerns with your vet.


A veterinary history and physical exam (including a dental exam) can go a long way toward identifying a cause. To rule out underlying disease, your vet may offer to perform diagnostic tests to examine blood cells, look for parasites and assess organ function.

Identify or Rule-Out Possible CausesDIAGNOSES

Dental & Oral Conditions, Generally
Tooth or Teeth Absent or Missing
Recurrent Airway Obstruction, RAO
Intestinal Parasitism (in Adult)
Equine Gastric Ulcer Syndrome, EGUS (in Adult)
Stress or Anxiety, Generally
Aging Changes, Generally
Periodontal Disease
Abscessed or Infected Molar, Periapical Abscess
Geriatric Dental Disease
Malabsorption Syndromes, Generally
Dental Overgrowths, Sharp Points
Pituitary Pars Intermedia Dysfunction, PPID
Chronic Systemic Disease, Generally
Ulcer, Gastro-Duodenal, Glandular Antral or Duodenal Ulcer (in Adult)
Protein-Losing Intestinal Diseases, Generally
Within Normal Limits, Normal for this Horse
Ascarid Worm Impaction
Right Dorsal Colitis
Equine Motor Neuron Disease, EMND
Retained Caps, Deciduous Teeth
Anemia, Generally
Equine Proliferative Enteropathy, EPE
Bastard Strangles
Abdominal or Internal Abscess, Generally
Tooth or Teeth Loose
Neoplasia, Tumor or Cancer, Intestine
Lymphosarcoma, Generally
Chronic Hepatitis
Liver Disease, Acute Hepatitis
Intestinal Lymphosarcoma
Pneumonia, Pleuropneumonia & Pleuritis, Generally
Neoplasia, Tumor or Cancer, Thorax
Liver Failure, Generally
Pyrrolizidine Alkaloid Plant Toxicity
Kidney Failure, Chronic Renal Failure
Locoweed Toxicity
Adhesions, Intra-Abdominal
Neoplasia, Tumor or Cancer, Stomach
Stomach Outflow Obstruction
Jimsonweed Toxicity
Neoplasia, Tumor or Cancer, Liver
Horsetail or Bracken Fern Toxicity
Neoplasia, Tumor or Cancer, Guttural Pouch
Leukemia, Cancer, Blood or Bone Marrow
Neoplasia, Tumor or Cancer, Kidney
Smoke Inhalation, Pneumonitis
Bastard Strangles
Intestinal Motility Disorder, Generally
Equine Infectious Anemia, EIA
Equine Herpesvirus 1 & 4, Rhinopneumonitis
Lyme Disease, Borreliosis
Equine Piroplasmosis, EP
Eastern, Western & Venezuelan Equine Encephalomyelitis
Trypanosomiasis, Surra, Mal de Caderas
Hepatic Encephalopathy
Moldy Corn Toxicity
Morning Glory Toxicity
Neoplasia, Tumor or Cancer, Brain
Neoplasia, Tumor or Cancer, Sinus or Nasal Passage
Multiple Myeloma
Cestrum Diurnum or Day Blooming Jessamine Toxicity
Besnoitia, Besnoitiosis
Clover Toxicity
Equine Grass Sickness
Lead Poisoning
Multisystemic Eosinophilic Epitheliotrophic Disease, MEED
Yellow Star Thistle or Russian Knapweed Toxicity
Diabetes Mellitus

Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health

Author: Doug Thal DVM Dipl. ABVP


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