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There are various clinical signs associated with excessive iodine intake including changes to the skin and hair, and bone abnormalities. Goitre – normally a feature of chronic iodine deficiency – may also occur because the prolonged intake of excessive iodine levels increases plasma iodine, which in turn has a negative effect on iodine uptake by the thyroid gland. In general, observations in dogs and cats are restricted to more subtle effects.
There are various clinical signs associated with excessive iodine intake including changes to the skin and hair, and bone abnormalities. Goitre – normally a feature of chronic iodine deficiency – may also occur because the prolonged intake of excessive iodine levels increases plasma iodine, which in turn has a negative effect on iodine uptake by the thyroid gland. In general, observations in dogs and cats are restricted to more subtle effects.
====Dog:====
====Dog:====
When dogs were given a single dose of potassium iodate delivering 100 mg iodine/kg bodyweight (BW) it caused anorexia and occasional vomiting. Higher doses of 200 and 250 mg iodine/kg BW caused anorexia, coma and death<ref>Webster, SH, Stohlman, EF, Highman, B (1966). “The toxicology of potassium and sodium iodates. III. Acute and subacute oral toxicology of potassium iodate in dogs”. Toxicol. Appl. Pharmacol. 8:185-192.</ref>. A lower (but still high) intake of iodine of 775 µg/kg BW/day in puppies was associated with bone abnormalities. This intake is equivalent to a dietary iodine content of about 17-18 mg/kg DM<ref>Castillo, V, Pisarev, M, Lalia, J, Junco, M, Rodriguez, M, Cabrin, R, Marquez, A (2001). “Commercial diet induced hypothyroidism due to high iodine. A histological and radiological analysis”. Vet. Quart. 23:218-223.</ref>.
When dogs were given a single dose of potassium iodate delivering 100 mg iodine/kg bodyweight (BW) it caused anorexia and occasional vomiting. Higher doses of 200 and 250 mg iodine/kg BW caused '''anorexia, coma and death'''<ref>Webster, SH, Stohlman, EF, Highman, B (1966). “The toxicology of potassium and sodium iodates. III. Acute and subacute oral toxicology of potassium iodate in dogs”. Toxicol. Appl. Pharmacol. 8:185-192.</ref>. A lower (but still high) intake of iodine of 775 µg/kg BW/day in puppies was associated with bone abnormalities. This intake is equivalent to a dietary iodine content of about 17-18 mg/kg DM<ref>Castillo, V, Pisarev, M, Lalia, J, Junco, M, Rodriguez, M, Cabrin, R, Marquez, A (2001). “Commercial diet induced hypothyroidism due to high iodine. A histological and radiological analysis”. Vet. Quart. 23:218-223.</ref>.
====Cat:====
====Cat:====
There are conflicting reports of the effects of excessive iodine in cats. For example, Kyle et al. fed a diet containing an iodine content of 21 mg/kg DM to cats for 5 months and observed no clinical abnormalities or changes in serum free thyroxine levels<ref>Kyle, A, Tartellin, MF, Cooke, R, Ford, HC (1994). “Serum free thyroxine levels in cats maintained on diets relatively high or low in iodine”. New Zealand Vet. J. 42:101-103.</ref>. In contrast, another study reported a significant depression in serum free thyroxine when cats were fed a dietary iodine level of 13.8 mg/kg DM for only two weeks<ref>Tartellin, MF, Ford, HC (1994). “Dietary iodine level and thyroid function in the cat”. J Nutr. 124:2577S-2578S.</ref>. Perhaps this was a temporary effect that eventually would have reverted to normal. It has also been suggested that excessive dietary iodine is a potential cause of feline hyperthyroidism but epidemiological studies have yet to identify a causal relationship<ref>Scarlett, JM (1994). “Epidemiology of thyroid diseases of dogs and cats”. Vet. Clin. North Am: Small Anim. Pract. 24:477-486.</ref>.
There are conflicting reports of the effects of excessive iodine in cats. For example, Kyle et al. fed a diet containing an iodine content of 21 mg/kg DM to cats for 5 months and observed no clinical abnormalities or changes in serum free thyroxine levels<ref>Kyle, A, Tartellin, MF, Cooke, R, Ford, HC (1994). “Serum free thyroxine levels in cats maintained on diets relatively high or low in iodine”. New Zealand Vet. J. 42:101-103.</ref>. In contrast, another study reported a significant depression in serum free thyroxine when cats were fed a dietary iodine level of 13.8 mg/kg DM for only two weeks<ref>Tartellin, MF, Ford, HC (1994). “Dietary iodine level and thyroid function in the cat”. J Nutr. 124:2577S-2578S.</ref>. Perhaps this was a temporary effect that eventually would have reverted to normal. It has also been suggested that excessive dietary iodine is a potential cause of feline hyperthyroidism but epidemiological studies have yet to identify a causal relationship<ref>Scarlett, JM (1994). “Epidemiology of thyroid diseases of dogs and cats”. Vet. Clin. North Am: Small Anim. Pract. 24:477-486.</ref>.