Abstract
Objectives The objective was to compare the effect on thyroid function in healthy, adult cats fed a limited-iodine food or conventional diet for 24 months. Methods Cats in the limited-iodine group (n = 14) were fed a commercial, dry food containing 0.2 ppm iodine on a dry-matter basis (DMB). Cats in the conventional diet group (n = 12) were fed an identical diet except that the iodine content was 3.2 ppm on a DMB. Both groups were maintained on their respective diets for 24 months. The median age of the cats at baseline was 3.2 years (interquartile range 2.4-4.3). Diagnostic samples were obtained for measurement of serum biochemistry parameters, thyroid hormone concentrations, complete blood count and urinalysis, and thyroid ultrasound examination was performed at baseline, 6, 12, 18 and 24 months. Results Median serum concentrations of free and total thyroxine and thyroid-stimulating hormone were within respective reference intervals for both test groups at all sampling intervals. Median urine iodine concentrations in the limited-iodine group declined significantly ( P = 0.0001) from baseline and were significantly different than conventional diet ( P ⩽0.0007). Ultrasound examination revealed no significant change in median thyroid height in the limited-iodine group at any time point. Conclusions and relevance Normal serum thyroid hormone concentrations and results of urinalysis and routine biochemical testing confirmed that the limited-iodine food was safely fed for 2 years to healthy, adult cats. Ultrasound examination showing that cats on limited-iodine did not develop a change in thyroid gland height was a further indication of the absence of iatrogenic hypothyroidism in the limited iodine diet group. These results support the lack of obvious side effects associated with feeding a limited-iodine diet for 2 years to healthy, adult cats, a situation that may occur in multi-cat households where healthy cats have access to a limited-iodine diet being used to manage cats with feline hyperthyroidism.