Is Your Dog Losing Weight? Common Causes and When It’s Time for a Vet Visit

Whether your dog is already thin or you have an overweight dog at home, weight loss in dogs can be a sign of an underlying health issue.  

In this article, you’ll learn potential answers to these questions: Why is my dog losing weight, and what should I do about it? 

Why Is My Dog Losing Weight?

Your dog could be losing weight for several reasons. Assuming that they haven’t been put on a weight-loss plan, it’s important to rule out medical causes.  

In puppies, the most common causes of weight loss include: 

• Gastrointestinal parasites: Parasites such as roundworms, hookworms, coccidia, and giardia are all common in puppies and can lead to weight loss. It can occur because the parasites are stealing nutrition from the puppy or causing diarrhea. 

• Viral infections: Parvovirus and other gastrointestinal viruses can cause poor appetite, vomiting, and diarrhea, all of which contribute to weight loss. 

• Poor diet after weaning: Some puppies struggle to transition from milk to solids. It’s also possible that the pet parent isn’t feeding a food formulated for puppies or isn’t feeding often enough. 

• Congenital defects: Though congenital defects are less common than the previously listed causes, it’s worth noting that some, like portosystemic shunt, can cause poor weight gain or weight loss.  

In adult dogs, common causes of weight loss include: 

• Poor nutrition: Low-quality diets, pickiness with eating, competition for food between dogs, and underfeeding can all lead to weight loss. 

• Gastrointestinal diseases: If your adult dog is having diarrhea or vomiting along with weight loss, it’s important to rule out conditions like inflammatory bowel disease (IBD), exocrine pancreatic insufficiency (EPI), food sensitivities or allergies, and gastrointestinal cancers. 

• Metabolic or endocrine conditions: Systemic (whole body) health issues outside of the gastrointestinal tract—such as diabetes mellitus, Addison’s disease, chronic kidney disease, and liver disease—can cause weight loss. 

• Dental disease: If your dog has fractured teeth or periodontal disease, both of which can make eating painful, they may lose weight.  

• Cancer: Cancers like lymphoma can cause weight loss because of an increased metabolic rate, decreased appetite, or organ dysfunction. 

• Stress or anxiety: Dogs with severe anxiety may lose interest in eating. This should be considered in dogs who are often destructive, struggle to relax, attempt to escape, pace, or have accidents in the home.  

• Cognitive dysfunction: Senior dogs with dementia may lose interest in food or forget to eat. 

When To Call Your Vet About Your Dog Losing Weight

It’s a good idea to call your veterinarian if you notice: 

• Any weight loss in puppies 

• Your adult dog is losing weight despite a normal appetite and food intake  

Other symptoms that may require a trip to the vet include: 

• Vomiting, diarrhea, or loose stools 

• Excessive thirst or urination 

• Dropping food while trying to eat 

• Lethargy or weakness 

• Muscle loss 

• Pot-bellied appearance 

• Heavy breathing, coughing, or exercise intolerance 

While weight loss itself is not an emergency, some conditions that cause weight loss—such as parvovirus—can be.  

If your dog has severe gastrointestinal symptoms, is struggling to move or breathe, collapses, or has jaundice, take your pet to an emergency veterinarian immediately. 

How Vets Diagnose the Cause of a Dog Losing Weight

After doing a thorough physical examination of your pet, your veterinarian will likely need to run diagnostics to figure out the cause of their weight loss.  

These diagnostics may include: 

• Blood work: This will test your dog’s organ function, look for signs of systemic infection, and check thyroid levels. 

• Urinalysis: Results can help rule out kidney disease and diabetes. 

• Fecal analysis: Your veterinarian will rule out fecal parasites. In puppies and unvaccinated dogs, a parvovirus test may also be done. 

• X-ray or ultrasound of the abdomen: Your veterinarian can look at your dog’s internal organs for abnormalities in size and shape. 

Depending on the test results, more advanced testing may be needed. 

You’ll want to give your veterinarian your dog’s complete diet history. This should include what food your dog eats, how often they eat, and any recent dietary changes. Make sure to consider treats and table scraps in their diet history. It’s a good idea to bring in food packaging or take photos of nutrition labels.  

You may also consider bringing a fresh fecal sample to the vet’s office. Fecal samples can usually be tested if they were collected within the last 24 hours and were refrigerated, but you should check with your veterinarian for specific instructions. 

Make sure to mention any symptoms—like loose stools—that you’ve noticed along with weight loss. 

Treatment for a Dog That’s Losing Weight

Treatments for a dog losing weight will depend entirely on their diagnosis, but they could include: 

• Dietary change: If you are feeding an inappropriate diet or your dog has food sensitivities, a new diet may be recommended. Hill’s z/d may be suggested for food sensitivities. A dietary change may also be recommended for certain systemic health conditions such as diabetes or kidney disease. 

• Supportive care/hospitalization: Dogs with weight loss due to severe illness may need hospitalization. Treatments could include IV fluids, tube feeding, anti-nausea medications, or pain medications. 

• Antibiotics: Antibiotics may be given if an infection is suspected or if your dog has a severe gastrointestinal condition, like parvovirus, that may increase their risk of sepsis. 

• Steroids: Some conditions, like IBD or certain cancers, may improve with steroids like prednisone. 

• Parasiticides or dewormers: If your dog tests positive for a parasite, they’ll need treatment. One option is NexGard Plus, which treats several types of parasites. A dog who tests positive for giardia is usually treated with fenbendazole and metronidazole.  

• Dental cleaning with or without tooth extractions: This is the standard treatment for dogs with dental disease. In some cases, a dental specialist can give specialized treatments like root canals to keep your dog’s teeth. 

• Additional treatments, like insulin for diabetes, will be recommended if a specific health condition is diagnosed. 

How To Prevent Your Dog From Losing Weight

Not all causes of a dog losing weight are preventable, but there are steps you can take to help keep your dog healthy and safe. They include: 

1. Keep your dog on parasite preventatives year-round.  

2. Make sure your dog stays up to date on vaccines. 

3. Say yes to annual labs to look after your pet’s systemic health. 

4. Attend wellness exams, as recommended by your veterinarian, to catch conditions early. 

5. Get any symptoms you notice in your dog checked out early rather than taking a wait-and-see approach. 

6. Feed a diet that is appropriate for your dog’s life stage and meets Association of American Feed Control Officials (AAFCO) standards. 

7. Keep your dog at a healthy weight to avoid systemic conditions like diabetes that can contribute to weight loss.