Castor & Pollux, Merrick Dog Treats Recalled For High Thyroid Hormone Levels, Hyperthyroid Dog Alerted Authorities

Merrick Pet Care is announcing a recall for three of its Merrick brand beef dog treats and two of its Castor & Pollux brand beef dog treats because they could contain elevated levels of beef thyroid hormone. Merrick was alerted to the problem after the FDA notified the company that a dog was diagnosed with diet-related thyrotoxicosis due to the consumption of beef jerky dog treats that were made using the thyroid glands of cows. The dog’s health has since improved according to the company press release, and the pup has fully recovered.

According to the company statement, “Dogs consuming high levels of beef thyroid hormone may exhibit the following symptoms: increased thirst and urination, weight loss, increased heart rate and restlessness. These symptoms may resolve when consumption decreases. If a dog consumes high levels for a long period of time, these symptoms may increase in severity and may include vomiting, diarrhea and rapid or labored breathing. If your pet has consumed the product listed and has exhibited any of these symptoms, please discontinue feeding and contact your veterinarian.”

The recall covers the following beef treat products:


Typically, how these manufacturing problems occur is when bovine thyroid tissue had been introduced into the neck trimmings inadvertently during the process of “gullet trimming,” a procedure that harvests muscles from the bovine larynx. Because thyroid tissue contains the active hormone thyroxine, and it is not destroyed by a pet’s gastric acid or digestive enzymes, it is absorbed into their bodies and remains active.

Although thyroid glands are not permitted in human-grade meat, and the USDA prohibits the use of thyroid glands and laryngeal muscle tissue for human food, thyroid glands can be used in pet foods.


The FDA explains how the problem can occur: “Pet food with increased concentrations of thyroid hormones likely contains animal gullets (laryngeal tissue) obtained most often from beef and lamb slaughter establishments used in the manufacture of pet treats and pet food. If a thyroid gland is not completely removed from a gullet and that gullet is then added to pet food or treats, remnant thyroid tissue could be a source of thyroid hormones.”

Although there is no law preventing the use of thyroid tissue in pet food, the practice is discouraged. The FDA advises manufacturers to ensure that their suppliers have fully removed thyroid glands from gullets and to “assess their suppliers’ practices and take steps to ensure that they are receiving raw materials and ingredients that do not contain thyroid hormone secreting tissue.”

Despite FDA’s recommendations, a recent study published in the Journal of the American Veterinary Medical Association on exogenous thyrotoxicosis in dogs, suggest the problem of thyroid tissue contamination may be widespread in the pet food industry.


If you have the product, please contact Merrick at 1-800-664-7387 from 8 a.m. to 5 p.m. Central Time Monday through Friday or so the company can answer questions and provide a refund. Or, visit Merrick’s website and fill out a form:


If you believe your pet has become ill from consuming a pet food, please provide the FDA with valuable information by reporting it electronically through their Safety Reporting Portal or call your local FDA Consumer Complaint Coordinator.

If you and your veterinarian think a pet food or treat is the source of a problem – save it – because your state agricultural or veterinary diagnostic lab may want to do testing. If you need more help, find out how to report a pet food complaint to the FDA.


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Mollie Morrissette

Mollie Morrissette, the author of Poisoned Pets, is an animal food safety expert and consumer advisor. Help support her work by making a donation today.