Can raw diets cause hyperthyroidism?

Neck meat and bone, trachea, and gullet products have grown in popularity in the pet food industry, fed as treats or as part of a raw diet. Chicken and turkey necks may be some of the most popular raw meaty bones due to their accessibility and low price. Pork, lamb, goat, and duck necks are also commonly used in raw diets. Trachea and gullet are advertised by treat manufacturers, raw food companies, and DIY raw feeders as ingredients that are great for their glucosamine and chondroitin content and as snacks that provide mental stimulation and prevent boredom.

But did you know that feeding too much neck meat, gullet, or trachea may put your pet at risk of developing hyperthyroidism?

Hyperthyroidism, also known as thyrotoxicosis, is a condition in which the body experiences an overproduction of a thyroid hormone called thyroxine. This condition is typically seen in elderly cats, and is rare in canines. In dogs, it is usually caused by a tumor on the thyroid gland, but it can also be caused by ingesting excess thyroid hormone in the diet.thyroid-gland

The thyroid gland that produces this hormone is located near the top of the neck, below the jaw.

When an animal consumes neck, gullet, or trachea products that contain thyroid hormones, the hormones are not destroyed by gastric acid or enzymes during digestion, so they get absorbed by the body. This means that a diet that contains an excessive amount of thyroid hormone can result in hyperthyroidism.

Hyperthyroidism causes the body’s metabolism to go into hyperdrive, resulting in weight loss, excessive water consumption, excessive urination, and increased heart rate [source]. Left untreated, it can eventually result in kidney failure or heart failure.

There have been multiple documented cases of dietary thyrotoxicosis in dogs that consume treats or raw diets containing too much thyroid hormone [source], including homemade raw diets [source], commercially available raw diets, and even commercially available treats and chews [source].

I was recently contacted by a fellow raw feeder whose two dogs both developed abnormally anxious and restless behavior. Tests revealed heartbeat irregularities. Further testing on one dog with a holter monitor revealed that the dog experienced 222 premature ventricular contractions (PVCs) in only 13 hours. PVCs are extra, abnormal heartbeats which, when seen in large quantities, can be a sign of cardiomyopathy and decreased oxygenation to the dog’s heart [source]. This owner identified the diet as a potential cause, realizing that they had been feeding more goat and lamb neck trim than usual over the past two months. After eliminating the neck trim from the diet for 5 days, the dog was tested again and they found zero PVCs in 24 hours of recording. Another test performed a month later confirmed that the dog was no longer experiencing high PVC counts. These results strongly support the idea that the dog’s issues were being exasperated by excess amounts of thyroxine in the goat and lamb neck trim.

Susan Thixon with TruthAboutPetFood.com wrote of another dog owner’s experience with dietary hyperthyroidism [source]: “…I heard from a pet food consumer whose healthy dog started to have a dry, ragged coat and showed some aggressive tendencies towards other dogs. This pet owner sent Dr. Jean Dodds some blood for testing and the results showed the dog’s thyroid levels were nearly 4 times normal. […] Dr. Dodds suggested to the pet owner to remove the current pet food […], and in two months time this dog’s thyroid went back to normal.”

To prevent this issue, raw feeders and any owners that feed chews made from neck, gullet, or trachea must be aware of the potential side effects of the ingredients they are feeding. These ingredients are perfectly fine in moderation, but it is important to monitor how much and how often they are fed. If you feed a commercial raw diet, check the ingredient list and/or contact the manufacturer to find out if the product contains neck, gullet, or trachea – and if so, how much.

If you feed a homemade raw diet, you must remember the importance of variety. For example, while relying on turkey necks as the sole source of bone content may be convenient and inexpensive for many raw feeders, introducing more variety can greatly limit the potential health issues that may be caused by excessive consumption of products that may contain thyroid hormones.

While there are occasional discussions on this subject in raw feeding groups and forums, there seems to be a myth that poultry necks are unaffected, and that raw feeders should only have to worry about restricting neck meat from beef, lamb, goat, or other larger animals. However, poultry necks still have thyroid glands on them too. Click here for a labelled photo of a chicken neck’s anatomy.

Owners feeding homemade diets should also be sure the diet they are feeding contains sufficient amounts of other nutrients that promote healthy thyroid function, such as iodine. Iodine is not present in adequate amounts in meat, bone, and organ alone, thus, many “prey model” raw diets that are not supplemented commonly do not contain the minimum requirement of iodine. But too much iodine can also cause an overproduction of thyroid hormone, so it is important to be aware of how much iodine your supplement contains, and to not exceed the recommended dosage instructions.

It is also important to keep up with your pet’s annual vet check-ups, including bloodwork. Annual bloodwork allows you to be proactive about your pet’s health and catch potential health issues that may pop up, with or without symptoms, before they become detrimental.

There is no research that suggests a specific amount when it comes to how much neck meat, gullet, or trachea can be fed to a dog or cat without developing hyperthyroidism. But by being aware of what and how much you’re feeding your pet, you will greatly decrease the risk of your pet developing thyrotoxicosis.

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