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Key takeaways

Unplanned weight loss in dogs is a common finding associated with many medical conditions.

  • Any illness or injury can lead to weight loss
  • Weight loss may be sudden with an obvious cause or gradual, requiring deeper investigation
  • Diagnostics for a dog with unexplained weight loss focus on determining the root cause of a dog’s weight loss
  • Treatment depends on underlying cause
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A closer look: Weight Loss in Dogs

Any illness or injury can lead to weight loss, if the condition is severe enough to decrease appetite or if it increases metabolism. Numerous diseases ranging from cancers to parasitic infections cause unexpected weight loss, even without a change in the dog’s appetite. In these cases, dogs either burn more calories to support recovery, or the disease negatively impacts digestion and use of nutrients.

Sometimes weight loss happens suddenly and has an obvious cause, such as excessive vomiting and/or diarrhea. Other times, weight loss happens more gradually, as a result of chronic illness. In some cases weight loss may be related to environmental conditions, such as competition for resources between dogs in the same household.

There are two major causes of weight loss: inadequate nutrient intake, and inability to process or retain nutrients. Many conditions cause both types of weight loss, as dogs often reduce their food intake voluntarily when they feel ill.

Weight loss is a common symptom associated with many conditions, ranging from mild to severe. Some causes of weight loss are life-threatening. Dogs unintentionally losing more than 10% of their normal body weight, or losing weight rapidly, require prompt veterinary attention, even without other symptoms.

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Possible causes

There are many conditions that can lead to weight loss. Generally, weight loss occurs as a result of inadequate nutrient uptake, lack of appetite, or abnormal digestion/metabolism.

Conditions associated with inadequate nutrient intake include:

  • Autoimmune diseases, such as masticatory myositis
  • Any illness associated with nausea
  • Any illness associated with anemia
  • Tumors, particularly oral tumors
  • Insufficient or inadequate diet
  • Physical injury
  • Competition between household pets for a shared food source

Many chronic diseases, such as cancer or renal failure, cause a dramatic weight loss condition called cachexia. In this condition, the body’s high demand for calories to support recovery processes results in breakdown of muscle tissue. Affected dogs lose weight rapidly, despite having a normal or increased appetite.

Risk factors

The severity of weight loss varies depending on the root cause. Some conditions lead to rapid weight loss, such as severe vomiting and diarrhea. Rapid fluid loss and dehydration exacerbates this. Chronic conditions, such as liver disease, typically cause slow weight loss over a long period. In some conditions, the onset of weight loss indicates a progression of underlying disease to a more severe state.

Since unplanned weight loss is associated with so many different underlying conditions, it is a very common clinical finding in dogs.

Testing and diagnosis

Diagnostics for dogs experiencing weight loss include:

  • Physical exam
  • Fecal analysis
  • Urinalysis
  • Bloodwork, including heartworm testing
  • Diagnostic imaging

Treatment varies depending on the cause of the weight loss.

Similar symptoms

Rapid weight loss is typically self-evident and easily identified. Dogs with significant weight loss have visible protruding bones, such as the spine, ribs, and pelvis.

Slow changes in weight over long periods are more difficult to identify without consistent, regular weight measurements. Annual wellness check-ups are helpful in identifying and tracking any weight changes over long periods. In many cases, dogs with weight loss from underlying conditions maintain a normal appetite, and show few other symptoms.

Associated symptoms


Courtney Barnes, BSc, DVM; Krista Williams, BSc, DVM; Ernest Ward, DVM - Writing for VCA Animal Hospitals
Jennifer Coates, DVM - Writing for PetMD

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