Why is My Old Dog Getting So Skinny?

A dog, just like a person, can lose weight for any number of reasons. Each dog has different nutritional requirements based on its age, breed, size, activity level, as well as other factors.

Some dogs can be skinny due to external factors like how active they are, or the quality of their food, while other dogs may get skinny due to internal factors like age or a health condition. Common reasons include:

1. Not getting enough calories

This is an external factor characterized by the dog simply not getting enough calories to fuel their body. Some reasons may be because another pet in the household is eating more than its share, the dog is unhappy with its food, or they do not have adequate time to eat everything in their bowl.

Dogs that have increased caloric demand like excessive physical activity, extended exposure to cold, pregnancy, or lactation, may benefit from some extra calories. These issues can easily be solved by ensuring the dog has privacy and time to eat, as well as enough food to meet their caloric demand.

If the dog does not seem interested in its food, it may be a good idea to switch them to something else. Remember that dogs’ stomachs are easily upset by sudden changes in diet, so changes should be made carefully and incrementally over a number of weeks.

2. Incomplete diet or deficiencies

Another external factor to a dog losing weight is an incomplete diet. This is a common issue for pets who are fed raw or homemade diets but can also be seen in dogs who eat a kibble diet that may not be nutritionally complete.

Although changing a dog’s diet may be in their best interest, it can be difficult to provide all the nutrients a dog needs in a raw or homemade diet. This is not to say that feeding your dog a homemade or raw diet is impossible, but it is more demanding and costly. Dogs require a delicate balance of essential nutrients for each meal, and even one missing ingredient can cause severe health consequences.

Even though it is less common, this can also be an issue when feeding normal dog food you find in the store. Cheap kibble brands and poorly packaged canned foods are both known to have less nutritional content, and can therefore lead to a deficiency in some necessary vitamins or minerals.

In both of these cases, it is necessary to ensure that your dog is receiving a complete diet so they will not lose weight. If a raw diet is still best for your dog, speak to your veterinarian and do plenty of research regarding your dog’s needs.

For nutritionally balanced kibble diets, make sure to buy a good brand and be aware of their ingredients. Many people choose to supplement their dog’s diet with commercial supplements or even tidbits of at-home ingredients like a raw egg or chopped-up fruits and vegetables.

3. Maldigestion

This is an internal issue where the body struggles to break down food. This is usually due to a lack of digestive enzymes and or bile acids and is often caused by a condition like exocrine pancreatic insufficiency.

Some other symptoms may include chronic diarrhea or even colitis. Because maldigestion is a bit more difficult to diagnose, it is best to see your veterinarian if you think this could be causing your dog to lose weight. It is usually easy to treat by supplementation of necessary enzymes and alteration of the dog’s diet, but more severe cases may require medication.

4. Malabsorption

Malabsorption is another internal issue and occurs when food is broken down by the body, but the nutrients cannot be absorbed. It can be caused by a number of health issues such as diseases that affect the pancreas, enzyme-related conditions, or intestinal disorders. Treating malabsorption will depend on its cause; so treatments can vary from dietary changes, supplementation of enzymes, or medication.

5. Illnesses or Diseases

Internal issues relating to the dog’s overall health are one of the primary reasons for weight loss. Some of the most well-known illnesses to cause weight loss are cancer, diabetes, and infectious diseases, all of which are related to weight loss due to the fact that they increase caloric demand.

With cancer alone, there are a multitude of reasons the dog may lose weight including loss of appetite, metabolic changes, direct effects of the tumor, chemotherapy, or radiation treatments. The best way to prevent weight loss in a dog with cancer is by feeding an energy-dense, high fat, moderately high protein, low carb diet.

Diabetes is another common reason for weight loss because the dog’s body is not producing enough insulin and cannot break down the sugars in the dog’s food. This forces the body to use its own fats and proteins for fuel.

Luckily, diabetes can be easily treated when managed properly. A good diet, plenty of exercise, and insulin injections are the suggested treatment plan for most dogs with diabetes.

Lastly, infectious diseases like distemper and parvovirus are both highly contagious and life-threatening. Other symptoms may include vomiting, and diarrhea, as well as difficulty breathing or coughing with distemper. Thankfully, these diseases are both easy to prevent through vaccination.

6. Hormonal imbalance

A hormone imbalance is an internal issue caused by a variety of conditions which create either an excess or lack of specific hormones. A common indicator for hormone imbalances is skin problems; the skin may be noticeably irritated, change in color, or consistency.

The dog’s weight, activity levels, and appetite are also likely to be affected by a hormone imbalance. Unfortunately, this is an issue which is difficult to recognize and diagnose, especially because it can be caused by many different conditions. If you notice any changes such as those listed above, your dog should be seen by a veterinarian or at your local animal hospital.

7. Intestinal Parasites

Parasites live in the dog’s body and steal nutrients from the dog. This is super common as the parasites can infect dogs in many different ways.

Hookworms are intestinal parasites that can be picked up through ingestion of the eggs, transferred from a nursing mother, and even burrow into the dog’s skin.

Another intestinal parasite is the roundworm, which looks similar to spaghetti, and can often be seen in the dog’s stool. Tapeworms are worms that look like pieces of rice and are usually picked up from ingesting a host carrying a tapeworm egg, like an adult flea.

Lastly, non-worm parasites like coccidia, giardia, and spirochetes are found in the intestinal tract and can come from infected soil, water, feces, food, other animals, and more.

Luckily, most intestinal parasites can be treated and even prevented with medications from your veterinarian. Regular flea preventatives and good hygiene are some of the best and easier ways to ensure your dog won’t have intestinal parasites.

8. Stress

Just like people, dogs can be affected by stress, and may even lose weight as a result of that. Changes in their home, routine, and environment are likely to cause some level of stress, and maybe even anxiety.

Fortunately, most of the stress will be eliminated as time goes on and the dog adapts to the new house, new baby or pet, new environment, or whatever has changed in their life.

If your dog still seems overwhelmed or uncomfortable after a few weeks, it may be beneficial to speak to a behavioral specialist about ways to alleviate their stress.

9. Old Age

Older dogs typically lose weight for one of three reasons. The first reason is that their body simply does not digest and absorb nutrients as well as it did when they were young. Secondly, is that a lack of appetite will cause them to eat less than they did during their prime.

Loss of muscle mass is the third reason, as older dogs tend to be happier to relax than run around all the time. This is not something that needs fixing like the other issues on this list, but just a natural part of their aging.


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Hannah Elizabeth is an English animal behavior author, having written for several online publications. With a degree in Animal Behaviour and over a decade of practical animal husbandry experience, Hannah's articles cover everything from pet care to wildlife conservation. When she isn't creating content for blog posts, Hannah enjoys long walks with her Rottweiler cross Senna, reading fantasy novels and breeding aquarium shrimp.

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