What Is Dietary Hyperthyroidism (Thyrotoxicosis) in Dogs?

Hyperthyroidism in dogs occurs where the thyroid gland produces excessive thyroid hormones. Hyperthyroidism in dogs is quite rare compared to cats.

When it does occur, it often stems from thyroid tumors, not diet and leads to to a sped-up metabolism and various health issues. Classic signs of dog hyperthyroidism may include weight loss despite increased appetite, vomiting, diarrhea, thirst, urination, and elevated heart rate.

By contrast, hypothyroidism (an underactive thyroid) is far more common in dogs, influenced by causes like autoimmune disease, atrophy, or breed predispositions. Aside from the normal triggers like cancer, atrophy etc, Dr Dobias has written a bit on the another unusual trigger for hypothyroidism in dogs.

Dietary hyperthyroidism is even rarer but has been documented, particularly in dogs fed raw animal parts that include thyroid tissue.

To learn more about how properly formulated raw diets are made and what ingredients reputable brands avoid, see our guide to best raw dog food in Canada and safe feeding practices. If you’re in Vancouver and ready to start, you can explore raw dog food for small dogs in Vancouver or choose bulk raw dog food in Vancouver for better value.

What the Research Shows: Raw Diets & Elevated Thyroid Hormones

As we mentioned earlier, dietary hyperthyroidism is even more rare. A few studies indicated that dogs fed raw animal parts contaminated with thyroid tissue had exogenous thyrotoxicosis and one paper was able to confirm that the slaughter facility included head meat. However, the other paper, which we couldn’t fully access didn’t explain whether head meat was fed or whether the dogs ate a commercially prepared raw dog food.

• The paper that was able to confirm exogenous thyrotoxicosis from head meat was from Vienna, Austria. We don’t know the standards of raw pet food in Austria but it seems to allow head meat.
• A case study published in the Journal of Small Animal Practice examined dogs with elevated plasma thyroxine (T4) who were fed raw meat diets or fresh/dried animal gullets. After changing their diets, thyroid hormone levels returned to normal and clinical signs resolved. This study was from Britain. Again not a Canadian or North American source, which could help indicate standards e.g. human grade.

To our knowledge, reputable commercial raw food manufacturers in Canada do not intentionally use head meat for their food although we’ve seen some Instagram posts from raw feeders when they go to the butcher. There is an important distinction between head meat and the neck below the thyroid.

• Normally, CFIA inspected human-grade processing requires removal of thyroid tissue. As most commercial raw food manufacturers in Canada purchase human grade meat, this lowers the likelihood of intentional inclusion of thyroid tissue. Contamination risk increases when the neck below the thyroid is included.
• The studies on exogenous thyrotoxicosis, focus on only beef and bison being the culprits. Nothing on kangaroo. The potential reason for beef and bison being culprits likely related to the size and hormone content of their thyroid glands.
• Although, kangaroo meat is exported from Australia, certain parts including the head and organs are likely not exported.

Why Raw Meat or Gullet Chews Can Be a Risk

The thyroid gland stores iodine and secretes thyroid hormones that remain stable even after freezing or drying, meaning thyroid tissue in raw meat can be active biologically. Gastric acid does not destroy thyroid hormone, and it can be absorbed in the intestine similarly to levothyroxine (a thyroid medication).

Parts like beef guts, neck meat, or head meat that are not properly trimmed can contain residual thyroid tissue. In commercial slaughterhouses, thyroid glands are generally removed during processing — but raw pet food ingredients sourced from local butchers, smaller suppliers, or non-human-grade meat may inadvertently include thyroid tissue.

Clinically Observed Cases vs. Practical Risk

Research suggests that continuous exposure to contaminated diet or untrimmed gullet chews (rather than an occasional bite) is what leads to thyrotoxicosis. In documented cases, dogs eating these contaminated diets long-term developed elevated T4 and clinical signs; when the diet was replaced, hormone levels and symptoms normalized.

Importantly, dietary hyperthyroidism in dogs is not as common as in cats, and most dogs with elevated thyroid hormones have underlying thyroid disease or tumors rather than diet-related causes.

Practical Tips to Avoid Dietary Hyperthyroidism in Dogs

Generally, we would recommend avoiding feeding head meat as the risk of contamination with thyroid glands is high. Small butcher shops and also some smaller pet food manufacturers might inadvertently risk contamination so we would avoid.

In terms of testing, we are not aware of any pet food manufacturer (kibble, can, raw or gently cooked) testing for thyroid hormones by batch. It will likely be super cost prohibitive and as such, as far as we know they just avoid head meat.

• From the papers on exogenous thyrotoxicosis, the animals that were affected were due to eating constantly contaminated products from beef. An occasional contamination did not seem to trigger this.
• Smaller animal parts appear to pose a lower risk potentially due to smaller thyroid glands.
  • We’ve worked with a holistic vet who fed his dogs, lamb necks every few days and none of his animals developed dietary hyperthyroidism with his oldest dog being 15 years for a Golden Retriever.
• Beyond raw red meats like beef and bison (which have larger thyroid glands), other sources can influence thyroid activity. For seafood vs land animals, generally kelp, seaweed and some fish will have high iodine levels and that can worsen hyperthyroidism.

Testing & Diagnosis

If dietary thyroid impact is suspected, the first step is a full thyroid panel (including T4, free T4, TSH), not just a single T4 measure. This helps differentiate between tumor-related disease and dietary or drug-induced hormone excess.

Veterinarians may also use imaging (ultrasound) to assess thyroid structure and rule out neoplasia. Once dietary hyperthyroidism is confirmed, then the food will need to be tested to confirm exogenous thyrotoxicosis.

Take your pet off the food and that should help the hormone levels return to normal.

Conclusion

Dietary hyperthyroidism in dogs is rare but has been documented in cases where raw diets were contaminated with thyroid tissue. Most affected dogs returned to normal thyroid levels after the contaminated food was removed, suggesting the condition is typically reversible.

The greatest risk is associated with larger animal parts such as beef or bison necks, head meat, and gullets when thyroid tissue is present. Diets very high in iodine, including those containing kelp or seaweed, may also influence thyroid hormone activity and should be used cautiously.

If you’re in Vancouver and worried about which raw dog food is safe, you can explore raw dog food for small dogs in Vancouver or choose bulk raw dog food in Vancouver for better value. Visit us for more in-depth chat at Moonlight Natural Pet Store.

References

1. Broome, Michael R., et al. “Exogenous Thyrotoxicosis in Dogs Attributable to Consumption of All-Meat Commercial Dog Food or Treats Containing Excessive Thyroid Hormone: 14 Cases (2008–2013).” Journal of the American Veterinary Medical Association, vol. 246, no. 1, 2015, pp. 105–111. https://pubmed.ncbi.nlm.nih.gov/25517332/
2. Köhler, B., C. Stengel, and R. Neiger. “Dietary Hyperthyroidism in Dogs.” Journal of Small Animal Practice, vol. 53, no. 3, 2012, pp. 182–184. https://pubmed.ncbi.nlm.nih.gov/22931400/
3. Government of Australian Government Department of Agriculture, Fisheries and Forestry. “Exporting Kangaroo Meat.” Department of Agriculture, Fisheries and Forestry, https://www.agriculture.gov.au/biosecurity-trade/export/controlled-goods/kangaroo#kangaroo-meat-supply-chain