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What is Underweight?

Even if you believe your dog looks fine, you may take him to the veterinarian and be surprised to find that he is underweight. Or, you may already know he is underweight even though you feel you feed him enough food. Some dogs eat much more than others and still have difficulty gaining weight, and several different breeds are simply smaller than others. The only way for you to know if your dog does not have enough weight on him is to take him to the veterinarian. 

There are many different reasons why your dog may be underweight, and several are typically not anything to be worried about. There are, however, conditions that may be more serious if you see your dog losing weight, especially rapidly. Reasons can include:

  • Insufficient diet
  • Underfeeding
  • Parasites
  • Diabetes
  • Teeth conditions
  • Disease
  • Medications

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Why Underweight Occurs in Dogs

If your dog is underweight, there are several reasons why this may occur. Oftentimes when dogs are adopted from unkempt environments or unhealthy previous lifestyles they may already be underweight. If your dog is losing weight even though you feel you are doing everything correctly in terms of diet, there may still be some reasons why it is happening. Reasons include:

Insufficient Diet

If a dog is consuming a diet that is insufficient for their dietary needs, such as a medium or large breed dog being fed small breed dog food, then that could cause a dog to be underweight. In addition, if you are feeding your dog a home-cooked diet, or raw diet, you may be unknowingly missing out on some key nutrients your dog needs to gain weight.


If your dog is underweight, you may not be feeding him enough at mealtime or enough times per day. Upon talking to your veterinarian, you will gain the knowledge of how much and how often to feed your companion.


Parasites, namely worms, can invade a dog’s gastrointestinal organs and prevent a dog from gaining weight. If your dog has intestinal worms, he may also be showing other symptoms, such as bloating.


Diabetes can cause a dog to be underweight. When a dog has an insulin shortage, he doesn’t get any nourishment from the cells. Therefore, the energy comes from fat and muscle.

Teeth Conditions

If your dog has painful teeth, such as abscessed teeth or inflammation of the gums, he may not want to eat much due to the pain in his mouth. Also, if a dog has a painful jaw or jaw muscles, this could cause painful chewing.


There are many diseases that can cause a dog to be underweight. Cancer, pulmonary conditions, abdominal diseases, and other illnesses can cause a dog to have trouble keeping weight on.


If your dog is taking certain medications, side-effects from the medications can cause him to lose weight and have trouble gaining it back. Consult your veterinarian for a possible change of prescription.

What to do if your Dog is Underweight

If you feel your dog is underweight, make an appointment with your veterinarian so this can be verified. Your veterinarian will perform a complete physical examination on your companion while asking you several questions about his diet. He will want to know how much food he eats and what type of food he enjoys. He will also ask questions pertaining to his lifestyle, such as how much he exercises and if he has an adequate amount of energy. He will also want to know if your dog is on any medications that may cause a side effect of lack of appetite.

If he feels you are not feeding your dog enough, he may have you take a little time to see if he gains weight after increasing his caloric intake. If this does not work, you will need to go back to your veterinarian for a more detailed examination. Your veterinarian may choose to perform blood work, a biochemistry profile, urinalysis, and possibly an ultrasound of the abdomen to check for any abnormalities in his gastrointestinal tract. He may also perform an endoscopy to take a closer look at his esophagus and his stomach. These various tests, as well as other tests as determined by your medical professional, will find any type of disease or other medical condition which can lead to your dog not gaining enough weight. 

Your veterinarian will also take a look at your dog’s mouth, teeth and throat area. He will be looking for inflammation of the gums or any teeth abnormalities. Once the test results come in, your veterinarian may have an idea of what is causing your dog to remain underweight.

Once your veterinarian comes to a diagnosis, he will explain treatment options for your companion. Once these treatment options begin to take hold, hopefully your companion will begin to gain weight.

Prevention of Underweight

In order to prevent your dog from becoming underweight, be sure to monitor his diet and always be observant of your dog. Keeping routine veterinary visits is very important in order to keep an eye on his weight. Being around your dog all of the time may make it difficult to see for yourself if he is losing weight over time, and a veterinarian visit on a regular basis can check that.

Some dogs have a lack of appetite and that prevents them from gaining weight. You can consult your veterinarian on diet advice and he may recommend home cooked meals or another non-traditional method of getting calories into his system.

If your dog has been diagnosed with an illness or disease, be sure to treat him as the veterinarian advises you to do so. He may be put on a special, high-caloric diet in order to help him have a healthy weight.

Cost of Underweight

If your dog is underweight, there are several different diagnoses as to why this may occur. The cost of treating intestinal parasites may be $300. The cost of treating an abscessed tooth may be approximately $1200. Treatment of diabetes mellitus may cost, on average, $3000.