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Lethargy in dogs can be a scary thing for pet owners to see. A lethargic dog may have some sort of stomach bug, or something else less serious — but there’s also a chance your pet could be suffering from one of many potential health problems. These are important to know, because some of these illnesses may need immediate attention from a veterinarian.

Here are some of the reasons why lethargy happens. Knowing these reasons could be critical to your dog’s health:

Kennel Cough and Lethargy in Dogs

One common cause of lethargy in dogs is kennel cough, or infectious tracheobronchitis. This affects the respiratory system, leading to a cough that often sounds like a honk. A dog with kennel cough may also have appetite loss, sneezing, and a fever.

Kennel cough is highly contagious. It can be spread through direct contact through the air, or from another dog’s food or water. Given this, it’s no surprise that kennel cough often spreads in places where dogs are together, like daycare or boarding facilities.1

Canine Heart Disease

lethargic dog | Ultimate Pet NutritionHeart disease can develop over time in dogs, and could also be caused by some sort of birth defect. Along with lethargy, there are several other signs of heart disease, including shortness of breath and a loss of appetite. If your lethargic dog won’t eat, get them to the vet to be checked out.

Weight gain, due to fluid accumulation in your dog’s stomach, is another one of the symptoms of heart disease, because a lack of proper blood circulation due to heart problems can cause fluid to build up in the stomach of a sick dog. If your dog’s behavior has changed in any way, that could also be a warning sign.2

Hemorrhagic Gastroenteritis

Hemorrhagic gastroenteritis (HGE) is an illness that can come on suddenly. In addition to lethargy, signs also include bloody diarrhea and vomiting. Our dog vomit color guide can be a great help when your dog is vomiting.

This illness can strike any type of dog, including puppies and older dogs. Certain breeds are more prone to problems, including:

  • Miniature Schnauzers
  • Yorkshire Terriers
  • Dachshunds
  • Poodles
  • Shetland Sheepdogs
  • Cavalier King Charles Spaniels

Potential causes of HGE include eating non-food items, stomach ulcers, stress, intestinal parasites, and intestinal bacteria.3

Liver Disease

A lethargic dog could be suffering from a disease affecting the liver — like leptospirosis. This can be caused by bacteria in stagnant water sources, such as puddles and ponds. Symptoms also include fever, red eyes, diarrhea, vomiting, coughing, and muscle pain.

lethargic dog | Ultimate Pet NutritionThis can be a life-threatening illness, so you may want to get to your vet as soon as possible if your dog is showing any of these symptoms.

Another disease affecting the liver that can lead to lethargy is hepatitis. There are different forms of this disease, just as in humans. Two of the most common are inflammatory and infectious hepatitis.4

Lyme Disease

Lyme disease occurs when an infected tick bites a dog. This disease causes microscopic bacteria known as Borrelia burgdorferi to enter the blood. It not only affects dogs and cats, but humans as well.

Ticks carrying Lyme disease can be found in just about any type of outdoor environment.

They live on tree branches, leaves, and even blades of grass. As a dog goes by, a tick will typically attach itself to the dog’s coat.

Lameness and lethargy are two common symptoms of Lyme disease. This illness can be very dangerous if not treated.5

Kidney Disease

Kidney disease occurs when the kidneys can’t properly filter waste products out of the blood. Some people think it means the kidneys can’t produce urine, but that’s not the case. Many dogs with the illness make plenty of urine. That urine just doesn’t carry waste out of the dog’s body as it should.

Kidney disease is usually associated with aging. In smaller dogs, it will typically begin between the ages of 10 and 14. In larger dogs, it could start as early as 7 years of age. It can take years before any sort of signs make themselves known.

Some of the other signs of kidney problems may include increased thirst, vomiting, diarrhea, mouth ulcers, and a loss of appetite.6

lethargic dog | Ultimate Pet Nutrition


This is one of the most severe, sudden illnesses that can strike a dog. Also known as gastric dilation-volvulus, bloat occurs when a dog’s stomach suddenly twists, closing off the openings to the organ. Bloat will typically occur when a dog exercises too soon after eating a large meal. Your vet can let you know how long your dog should wait to exercise after eating.

Signs of bloat include lethargy, vomiting, and restlessness. Often times, an affected dog will collapse. Get your dog to the vet as fast as you can if you have any reason to suspect bloat has occurred.7

How Does a Veterinarian Treat Lethargy?

Lethargy is a sign of an illness, and not an illness itself. In order to determine the best way to address this problem, vets must first find out what’s causing the problem. As you can see, there can be a lot of potential reasons for lethargy in dogs.

Expect your veterinarian to ask several questions about your pet. When did the lethargy begin? Has it gotten worse over time? Is your dog eating normally, or has he or she had a loss of appetite? Has there been a change in dog food?

There may be other tests needed in order to see if an infection is the cause of your dog’s lethargy, or if there is some other issue to blame.8

Don’t Panic, But Take Action

Dog owners never want to see their four-legged friends suddenly lose their zest for life. Most are used to them running around the yard, tails wagging, enjoying a perfect dog’s life. When a dog is lethargic, it can be easy to expect the worst. Just remember to stay calm, and don’t hesitate to get your dog to the vet if you expect something is wrong.

In many cases, a dog might simply have an upset stomach or something else that’s relatively minor. If your pet isn’t eating like normal, they might just have a temporary bug. But sometimes, it’s better to be safe than sorry. Your vet can get to the root of the problem, and help get your dog’s health back on track.

Learn More:
Dogs and Milk – Not a Great Combination
Why is My Dog Scratching So Much?
Why is My Dog Breathing Fast?