Effect of dietary soy on serum thyroid hormone concentrations in healthy adult cats.

OBJECTIVE: To compare effects of short-term administration of a soy diet with those of a soy-free diet on serum thyroid hormone concentrations in healthy adult cats. ANIMALS: 18 healthy adult cats. PROCEDURE: Cats were randomly assigned to receive either a soy or soy-free diet for 3 months each in a crossover design. Assays included CBC, serum biochemical profile, thyroid hormone analysis, and measurement of urinary isoflavone concentrations. RESULTS: Genistein, a major soy isoflavone, was identified in the urine of 10 of 18 cats prior to dietary intervention. Compared with the soy-free diet, cats that received the soy diet had significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations. The T3/fT4 ratio was also significantly lower in cats that received the soy diet. Although the magnitudes of the increases were small (8% for T4 and 14% for fT4), these changes resulted in an increased proportion of cats (from 1/18 to 4/18) that had fT4 values greater than the upper limit of the laboratory reference range. There was no significant effect of diet on any other measured parameter. CONCLUSIONS AND CLINICAL RELEVANCE: Short-term administration of dietary soy has a measurable although modest effect on thyroid hormone homeostasis in cats. Increase in T4 concentration relative to T3 concentration may result from inhibition of 5'-iodothyronine deiodinase or enhanced T3 clearance. Soy is a common dietary component that increases serum T4 concentration in cats.

Spontaneous pneumothorax in two cats with small airway disease.

Two adult domestic shorthair cats were examined because of pneumothorax. Neither had a history of trauma, and spontaneous pneumothorax secondary to small airway disease was diagnosed. In both cats, treatment consisted of thoracocentesis for evacuation of air and administration of anti-inflammatory agents. One cat had multiple episodes of pneumothorax and eventually died; the other had only a single episode of pneumothorax. Small airway disease should be considered as a potential underlying cause in cats that develop spontaneous pneumothorax. Additionally, the potential for pneumothorax should be considered in cats with small airway disease, particularly when clinical signs suddenly become much worse.