Can Feeding Your Pet This Raw Food Cause Thyroid Problems?

Hungry Pet Dog

Story at-a-glance -

  • Hyperthyroidism is a very rare condition in dogs and when it does occur, is usually caused by an aggressive thyroid tumor. That’s why three recent studies linking the disease in a handful of dogs to their raw diets are worth mentioning.
  • Hyperthyroidism is a condition in which the thyroid glands over-produce thyroid hormone, causing a constant state of metabolic hyperactivity. Clinical signs include increased thirst and appetite, excessive urination, vomiting, weight loss, and increased heart rate. Left untreated, the condition can cause heart and kidney failure.
  • In three recent studies, a small number of dogs were diagnosed with dietary-related hyperthyroidism caused by ingesting active thyroid tissue contained in raw diets. Gullets, head meat, and animal necks were the suspected culprits.
  • While the studies involve a very small sampling of raw fed dogs, if you’re concerned about hyperthyroidism in your own pet, we recommend offering a variety of protein sources so that your dog isn’t eating a steady diet of foods that could contain active thyroid tissue.
  • We also recommend taking your dog in for regular wellness visits with your veterinarian, at which time his or her blood thyroid hormone levels can be checked.

By Dr. Becker

Hyperthyroidism is typically a condition seen in older cats. It is very rare in dogs, but three recent studies linking the condition in dogs to certain aspects of their raw diets are worth noting for all of you who also feed raw.

In most cases of canine hyperthyroidism, the cause is an aggressive thyroid tumor that over-produces thyroid hormone. The only other recognized cause is the ingestion of thyroid hormone from other sources, which seems to be what occurred in the recently studied dogs.

What Is Hyperthyroidism?

Your dog's thyroid glands are located just below the larynx, next to the trachea. (See illustration here.) The glands secrete thyroid hormone, which regulates metabolism. Decreased levels of thyroid hormone in the blood slow down the metabolism; increased levels speed things up. Your dog's body temperature, heart rate, food utilization, and other functions depend on the appropriate level of thyroid hormone in the bloodstream.

Hyperthyroidism means the glands are working overtime, secreting too much hormone, which causes a constant state of metabolic hyperactivity. Animals with the condition typically lose weight despite being constantly hungry, drink excessive amounts of water and urinate excessively, have increased heart rates, and also vomiting. Left untreated, hyperthyroidism can result in heart and kidney failure.

Three Recent Studies Reveal Components of Some Raw Diets Can Cause Hyperthyroidism in Dogs

In a 2012 study published in the Journal of Small Animal Practice,1 12 raw fed dogs were evaluated for elevated plasma thyroxine (thyroid hormone) levels. Six of the dogs had symptoms of hyperthyroidism, while six had no clinical signs. After a change in diet, 8 of the dogs' thyroxine levels returned to normal and their symptoms resolved.

The study authors concluded that:

"Dietary hyperthyroidism can be seen in dogs on a raw meat diet or fed fresh or dried gullets. Increased plasma thyroxine concentration in a dog, either with or without signs of hyperthyroidism, should prompt the veterinarian to obtain a thorough dietary history."

In a 2013 case study from Vienna, Austria,2 two dogs belonging to the same owner had clinical signs and plasma thyroxine levels suggesting hyperthyroidism. The dogs also underwent ultrasound imaging of their necks, revealing normal-sized thyroid glands. The veterinarians treating the dogs suspected diet-related hyperthyroidism caused by feeding head meat containing thyroid gland tissue. They confirmed their findings by talking with the slaughtering plant, measuring iodine concentrations in frozen samples of the same head meat the two dogs were fed, and testing thyroxine levels in five additional dogs fed head meat from the same source. After the diet of the two dogs was changed, their thyroid hormone levels dropped and symptoms disappeared.

According to Dr. Ken Tudor writing for PawNation, an unpublished 2014 study also confirms the presence of beef necks and thyroid tissue in raw dog treats. Since a dietary change (unspecified) resulted in normalized blood thyroid levels and disappearance of symptoms, it appears raw thyroid tissue was the root cause of the dogs' hyperthyroidism.

What Does This Mean for Your Raw-Fed Dog?

Many people don't realize the thyroid glands aren't the only place active thyroid hormone secreting tissue can be found. Studies have shown that minute amounts of active thyroid tissue are often located all along the trachea, even into an animal's chest. Dogs fed raw animal necks can absorb thyroid hormone from the still-attached thyroid glands or other pieces of active thyroid tissue in the neck. And as the three recent studies prove, the amount can be enough to cause symptoms of hyperthyroidism.

In raw diets for dogs, the most likely source for thyroid tissue is in meaty bones including the necks of chickens and other small prey animals like rabbits, as well as the necks of large livestock.

To avoid diet induced hyperthyroidism in your raw fed pet, my recommendation is to make sure you are feeding a variety of protein sources and cuts of meat (thigh meat, etc.) so that your dog isn't eating a steady diet of raw meaty bones/necks that could contain active thyroid tissue.

If your pet is a healthy, raw-fed dog, it's not necessary to go out of your way to avoid foods that may possibly contain thyroid tissue. The studies I mentioned above involve a very small number of dogs that I suspect were eating the same cuts of meat (necks) for a prolonged period of time. Thankfully, their hyperthyroid conditions were easily reversed with a simple dietary change, but this study reinforces my belief that pets need a variety of different meat sources (and body parts) for overall health and wellbeing. So if you've been feeding poultry necks regularly as the foundation of your dog's raw food diet, consider changing up your recipe to include other cuts (wings and backs) and diversify your protein sources.

I also recommend you keep an eye out for symptoms of hyperthyroidism (and any other possible illness) in your pet, and see your veterinarian for regular wellness checkups that should include measuring your dog's blood thyroid hormone levels.