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7 Causes of Weight Loss in Pets

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Sudden Weight Loss in Pets

By John Gilpatrick

 

While controlled weight loss, planned in conjunction with a veterinarian or veterinary nutritionist, is incredibly beneficial for pets that are overweight, there are certain forms of weight loss in animals that can be concerning.

 

“If a patient is on a weight loss plan for obesity, vets generally recommend about one to two percent loss of bodyweight per week,” says Lara Bartl, DVM, DABVP, assistant professor at the Virginia-Maryland College of Veterinary Medicine at Virginia Tech University, but unless you are trying to achieve weight loss, she adds, any weight loss should be considered significant and investigated.

 

Unplanned or rapid weight loss may be symptomatic of something serious. Here are the most common reasons for unwanted weight loss in pets:

Parasites

Cailin Heinze, assistant professor of nutrition at the Cummings School of Veterinary Medicine at Tufts University, says cases of weight loss related to parasites aren’t as common as they once were because many pets are on monthly heartworm protection drugs. However, not all products are equally effective against all worms.

 

“Whipworms, in particular, aren’t killed by a lot of products,” she says. These are more common in dogs than in cats and pets will contract these by ingesting contaminated food or water. Along with weight loss, symptoms of an intestinal parasite in pets can include include vomiting (intermittent or persistent), soft stool, diarrhea and/or decreased appetite. Using a broad spectrum de-wormer, Heinze says, is one of the first things vets might do to help a dog with these symptoms.

Cancer

Intestinal cancer (lymphoma and/or lymphosarcoma) is one that causes weight loss in both dogs and cats, Heinze says. While it’s more common in older dogs than cats, it’s a serious diagnosis. The tumor may appear in the stomach, intestines, or rectum and other symptoms include vomiting, poor appetite, and abdominal pain. Additionally, any type of cancerous process can cause weight loss, including cancer of the gastrointestinal tract, liver, gallbladder and kidneys. 

Kidney Disease

Unlike some of the other conditions for which weight loss is a symptom, pets with kidney disease won’t start dropping pounds right away. “If they’re only getting diagnosed after they’ve started losing weight, they’ve probably had the disease for a long time,” Heinze says.

 

The same is true for hyperthyroidism, a disease for which weight loss is a symptom in cats but not dogs, Heinze says. The difference: pets with kidney disease will drink and urinate a lot, while cats with hyperthyroidism eat to excess and have excessive thirst (polyuria). 

Advanced Heart Disease

Like kidney disease, pets with heart disease won’t start losing weight immediately. In fact, some dogs may gain weight, despite a loss of appetite (the cause: bloat).

 

Generally speaking, Heinze says loss of appetite is the easiest way to tell if your pet’s weight loss is concerning or not. If you’ve noticed a small amount of unplanned weight loss, try adding calories to their diet, she says. “If they eat more and gain weight, they’re probably OK.”

 

In addition, make sure you’ve isolated that pet’s food from the food of other pets in the house. The experiment must be controlled, which also means vigilance against feeding table scraps or too many treats.

Dental Disease

Oral pain, Bartl says, may lead to weight loss in pets, as dogs and cats will have a hard time chewing hard kibble when they’re dealing with an abscess or other gum problem. Treatment for the underlying condition should address the weight loss problem, but monitor your pet’s appetite closely to make sure it’s back on track. 

Changing Food

Not all cases of seemingly inexplicable weight loss are explained by a disease or a condition. Heinze says one of the most common explanations for weight loss is changing your pet’s food.

 

“I have had people come to me because their dog is losing weight. They had a complete work-up done and no one could find anything wrong,” she says. “It turns out the dog’s food was changed. The owners were feeding it the same amount every day, but the new food had 20 percent fewer calories.”

 

Heinze says it’s easy to miss this because foods are marketed in seemingly haphazard ways when it comes to nutrition. “Sometimes, a food that is marketed for overweight pets – it might say ‘healthy weight’ or ‘weight maintenance’ or ‘reduced calorie’ – might have more calories than ‘regular’ food,” she says.

 

If you plan to change your pet’s food, check the ingredient labels of both brands and make the swap based on calories. Heinze says that if you’re looking for food that’s truly meant to help your dog lose weight, look for the word “light” on the label.

Stress

This is not as common as medical causes, Bartl says, but stress can cause changes in a pet’s appetite and should not be overlooked. She lists changes in the household and the addition of a new pet as possible sources of stress-induced weight loss.

 

Concerned your pet is stressed? Look for these five signs of stress in cats or find out how to calm an anxious dog.

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