Feeding of biologically appropriate raw food (BARF) including gullet is popular: Due to the close anatomical position of the thyroid gland and the respective muscle tissue such diets are likely to be contaminated with thyroid gland tissue and may cause alimentary thyrotoxicosis. However, as controlled studies are missing, it is unclear which effect the absorbed total thyroxine (T₄) and triiodothyronine (T₃) may have on the thyroid hormone status. Because T₄ levels are still routinely checked in the elderly dog and commonly in dogs suspicious of behavioral issues it would be of high diagnostic interest, if potential thyroid gland feeding may interfere with the diagnostic approach. Therefore, the present study aimed in investigating the short term effect of thyroid gland feeding on the thyroid hormone concentration in dogs. Bovine thyroid gland from the slaughterhouse (0.5 g/kg body weight) was fed after 12 h fasting together with a complete dry diet. Blood samples were taken 19 days before the experiment in order to verify euthyroidism in the healthy beagle dogs (n=5). On the day of the feeding experiment blood was taken before (0 and 4, 8, 24, 52 h as well as 6 days after feeding. In the samples T_4-, free T_4-, T₃ and thyroid stimulating hormone (TSH) as well as thyroglobulin autoantibodies (TgAA) were measured either using an automated chemiluminescence immunoassay (Immulite® 1000 System, Siemens Diagnostics, USA) or a commercially available TgAA assay (Oxford Laboratories, MI, USA). No dog had TgAA. After feeding thyroid gland there was an increase up to 7.8 fold basal levels of T₄, free T₄ and T₃ serum concentrations. Serum levels returned to basal levels after 52 h, however, three of five dogs showed T₄ and fT₄ concentrations below the reference range 52 h and 6 days after single controlled thyroid gland feeding. TSH levels were suppressed after feeding for 52 h. None of the dogs showed any clinical symptoms of hyperthyroidism. Feeding of thyroid tissue to healthy dogs resulted in distinct effects on the thyroid hormone blood concentration. Initially single feeding of thyroid gland lead to considerably higher T₄ levels but afterwards also to lower T₄ and fT₄ concentrations. Therefore, if euthyroidism should be diagnosed, administration of dog food containing thyroid gland should be carefully ruled out for the last seven days.

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