Dietary Hyperthyroidism in Raw Fed Dogs- The "Dangers" of feeding certain raw meaty bones

June 6, 2021

Dietary induced hyperthyroidism/hypothyroidism in dogs & cats...
"Will feeding my dog chicken necks lead to thyroid issues? Are feeding necks in my dog's raw diet an issue? Is feeding poultry necks to my dog risky? Am I supposed to limit my raw fed dog's intake of poultry necks to prevent hyperthyroidism?"

These were all questions that kept popping up repeatedly from other pet parents who feed their pets a balanced raw diet, and it admittedly left me scratching my head (wait, feeding poultry necks can be problematic?? What am I going to do with the $h!t load of duck necks I just ordered from RFM??!!). Prior to these pet parents voicing their concerns, I wasn't actually aware of the potential link between feeding necks and dietary hyperthyroidism. 

If you are already a member of our private facebook group, Raw Feeding University, then you would already know we have a "File" that is shared with members and it discusses the topic of dietary hyperthyroidism. Because this file is only accessible to members of RFU, I wanted to be able to share what I found in my research on the topic, and make that information accessible to any raw feeding parents who find themselves in a situation like I was in- sitting with a freezer full of necks and wondering if you have to curry them and eat it for the next 2 years or if it would still be okay to feed to your dogs. I also wanted to see if there was any published scientific data to help me form my own opinions, irrespective of the files in our facebook group. 

What I was able to find on the topic of dietary hyperthyroidism has been shared below...

Hyperthyroidism in dogs caused by consumption of thyroid-containing head meat- F. K. Zeugswetter

“Two female spayed dogs belonging to the same owner were admitted for further examinations because of clinical signs and laboratory values compatible with hyperthyroidism. Sonography of the ventral aspect of the neck revealed small thyroid glands in both dogs.
The hypothesis that the dogs suffered from alimentary hyperthyroidism caused by feeding head meat containing thyroid gland tissue was confirmed by consultation of the slaughtering plant, determination of iodine concentrations in deep-frozen samples and hormone measurements in 5 other dogs receiving head meat from the same supplier. After changing the diet, thyroxine concentrations declined and clinical signs were no longer observed.”

“Frozen ground-beef samples were sent to the Austrian Agency for Health and Food Safety (Linz, Austria) for iodine determination. Iodine was measured using inductively coupled plasma mass spectrometry (ICP-MS) after alkaline extraction. The analysis revealed iodine concentrations (mean ± SD) of 9.43 ± 2.36 mg/kg (average iodine of muscle tissue ~ 0.02 – 0.15 mg/kg; Flachowsky et al., 2007). After selective removal of visible thyroid tissue during neck trimming, iodine concentrations dropped below the detection limit of 0.08 mg/kg. Thyroxine was additionally measured in 5 other dogs fed with head meat from the same supplier. This group consisted of 4 female Rhodesian Rhidgebacks [Fig.1 dogs 3 – 6] and one female Miniature Pinscher [Fig. 1 dog 7], ranging in age from 1 – 6 years. Four of these dogs also showed hyperthyroxinemia (Fig 1, dogs 3, 4, 5 and 7), but only 2 had shown mild clinical signs (restlessness and aggressiveness). TSH was below the detection limit of 0.03 ng/ml in all dogs.”

Given the ethical issues of inducing hyperthyroidism in dogs, there are no large sample-size cohorts to grapple with when investigating this issue. 

This article details a case study about 2 dogs from the same owner who exhibited symptoms and test results consistent with hyperthyroidism. It was determined that they developed hyperthyroidism from their diet after ultrasound analysis showed normal sized thyroid glands, indicating that the dogs did not develop thyroid tumours- which would increase hormone production, and confirmed by the lack of thyroglobulin, triiodothyronine and thyroxine autoantibodies from canine blood analysis. 

Going one step further to prove causation, samples of ground beef from the owner’s supplier were analysed and shown to have significantly elevated iodine levels consistent with high concentrations of iodine-containing thyroid hormones (see figure). 

Dietary hyperthyroidism in a Rottweiler- S. Cornelissen

“In this report, a clinical case of dietary hyperthyroidism in a dog is described. An eleven month-old, male, intact Rottweiler was presented because of panting, weight loss and increased serum total thyroxine concentration. A complete history revealed that the dog was fed a bone and raw food diet, which made dietary induced hyperthyroidism very likely. Other possible differentials were excluded after a thorough diagnostic work-up. Finally, after changing towards a traditional commercial maintenance diet, the clinical symptoms resolved and thyroid blood values normalized. In every dog with an increased serum total thyroxine concentration, with or without clinical signs of hyperthyroidism, a thorough dietary history should be obtained. Owners should be informed that raw food diets tend to be nutritionally imbalanced, carry the risk of bacterial contamination, and have other safety problems. Therefore, veterinarians should recommend against feeding these diets.”

“Dietary hyperthyroidism can occur in dogs fed raw food diets. The work-up of every dog with an increased serum TT4 concentration, with or without clinical signs of hyperthyroidism, should include a thorough dietary history. Owners should be informed and veterinarians should recommend against feeding these diets.”

This second case study on a single Rottweiler puppy details thoroughly how the vets were able to diagnose the puppy with dietary hyperthyroidism, yet did not investigate the source in the dogs diet. 

The article takes a much more partial stance than the one previously reviewed, dedicating the majority of the discussion section arguing against raw food diets and the health risks they present due to nutritional imbalances, bacterial exposure, and safety issues with ingesting bones. An investigation into whether the Rottweiler puppy had been ingesting neck-meat would have given more nuance to their critique of (improperly executed) raw food diets.

Exogenous thyrotoxicosis in dogs attributable to consumption of all-meat commercial dog food or treats containing excessive thyroid hormone: 14 cases (2008–2013)- Michael R. Broome

“Two recent reports of thyrotoxicosis in dogs secondary to consumption of diets containing raw meat or dried gullets, presumably contaminated with thyroid tissue, have also been published. To the authors’ knowledge, there are no other published reports of thyrotoxicosis in dogs secondary to consumption of commercially available dog foods or treats. The purpose of the study reported here was to describe the clinical, laboratory, and scintigraphic findings in dogs with exogenous thyrotoxicosis attributable to consumption of commercially available dog foods or treats.”

“All 14 dogs were being fed all-meat or meat-based varieties of commercially available dog foods or treats at the time of diagnosis of exogenous thyrotoxicosis. All samples or descriptions of the suspect foods or treats provided by clients were of a similar form (sliced or rolled jerky style). Owners of the first 3 dogs identified in this series provided descriptions of the suspect products, including form, predominant color of the bag, and the store from which the product was purchased, but without sufficient brand information to ensure confident identification of the specific product involved... 
Analysis of the 7 samples of food or treats that were tested revealed that the median concentration of immunoreactive T4 was 1.52 µg of T4 /g, whereas that for samples of commercial dog food used as controls and for beef and liver samples was 0.38 µg of T4 /g and 0.30 µg of T4 /g, respectively (Figure 2). Differences were not compared statistically because independence of all samples could not be confirmed... All 14 dogs of this report developed a reversible thyrotoxicosis following consumption of various commercially available meat-based dog foods or treats that were known or suspected to contain high concentrations of T4, presumably secondary to contamination with thyroid tissue.
The small number of cases of exogenous thyrotoxicosis that we identified over a 5-year period suggests that the problem of contamination of commercial dog food or treat products with thyroid tissue may be sporadic. Alternatively, the number of dogs identified could be limited by the nature of the products identified as containing high concentrations of thyroid hormone (ie, most were labeled as dog treats). The risk of thyrotoxicosis caused by consumption of meat-based products contaminated with thyroid tissue should be proportional to the percentage of the dog’s caloric intake of the T4 -containing product.”

In this article, cases of dietary thyrotoxicosis were found as a result of ingesting commercial dog food/treats rather than from a raw food diet as we’ve previously seen. 

While the brands of treats are not explicitly discussed or compared with jerky/treats with normal levels of T4 hormone, comparing hormone levels with beef muscle and beef liver furthers the point that the body part from which the meat comes from determines whether it is contaminated with thyroid hormone (see figure below). 

Although rare, dietary hyperthyroidism can occur in dogs regularly consuming food contaminated with high levels of thyroid hormone. While data on the matter is limited to case studies on dogs admitted to animal hospitals with clinical symptoms, promising causation was demonstrated by full resolution of symptoms after changes in diet. 

The dietary items that caused thyrotoxicosis were found to be contaminated by thyroid tissue, which is normally separated from muscle tissue during processing of ground meat. In order to avoid inducing hyperthyroidism through diet, intact large-animal necks (namely bovine) should definitely not be fed on a daily basis. And as a precautionary measure, this should be extended to all species of animal necks/meats that stand a higher chance of being contaminated with thyroid tissue (including gullets & tracheas; see diagram below for placement of human thyroid gland to help w/ the visualisation).

(source; no copyright infringement intended)

It is not recommended to feed your pets the bones of larger animals (ex. beef bones) within a balanced raw diet, as they pose a major tooth fracture risk. This includes weight bearing bones in general. The exception would be when the bones are ground into premade balanced mixes, or when they have been turned into powdered supplements like bone meal. 

So can I still feed poultry necks, including, but not limited to, chicken necks, duck necks, goose necks etc, to my dogs?
Any meat contaminated by thyroid tissue will pose a risk, as it is directly linked to an increase in thyroid hormones present within the meat. This is why the safest practice, and what I personally do, is to rotate the raw meaty bones being fed within a balanced raw diet for your dogs. 

This means, not feeding animal necks (or even those with heads still attached to the neck portion, gullets, and/or tracheas) on a daily basis. If you meal prep, prepare more than one recipe, making sure that your other recipes include a different raw meaty bone (like chicken/duck wings, duck feet, rabbit bones, chicken backs, lamb ribs etc...). Then rotate the recipes being fed throughout the week!

What I now do is, once prepping 2-3 recipes, on day 1, I'll feed a recipe containing neck as my raw meaty bone. Then on days 2 & 3, I feed a different recipe that does not contain any neck bones. On day 4, I might reach for the recipe containing neck bones again. This way, I am still able to utilise all the meat and bones I have in my freezers and nothing goes to waste, while still limiting the risk of inducing dietary hyperthyroidism in my dogs. 

How can I tell if there is thyroid tissue in the meat I am feeding?
Short answer is, you cannot tell if the meat or raw meaty bones you are feeding contain thyroid tissue by just looking at it, and you also cannot tell by the smell (unless you see the entire gland still physically attached). 

Thyroid tissue is referring to tissue coming from the thyroid gland, which also contains thyroid hormones because that is where the hormones are produced. 

Spectrometry is chemical analysis by measuring the mass-to-charge ratios of a molecule‘s characteristic bonds, and this is what is done in order to detect the presence of thyroid hormones. 

What should I do if my dogs are diagnosed with dietary hyperthyroidism?
If your dog or dogs do in fact develop a case of dietary hyperthyroidism, you should immediately remove the source of meat containing thyroid tissue from their diet. 

Eliminating the source should allow for your dog or dogs to rebound fairly quickly. It is also important that you feed a balanced raw diet, as over-feeding these contaminated portions of meat, coupled with an unbalanced diet, will only exacerbate the issue. 


Please consult physicians/veterinarians, and/or other trustworthy science-based sources for advice on human and animal dietary questions.

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