The effects of different maternal dietary iodine concentrations on Japanese quail I. Thyroid status of hens

Japanese quail Coturnix japonica were used as a model system for studying the effects of different levels of dietary iodine (I) supplementation (0–1200 μg I/kg of purified diet) on thyroid function and egg-laying in adult galliform birds. Quail have the ability to adapt their thyroid function to a wide range of dietary I intakes. We measured thyroidal 125I uptakes, stable I concentrations in serum and thyroid glands, and triiodothyronine (T 3) and thyroxine (T 4) concentrations in thyroid glands and serum. Body weights of the hens as well as egg production, egg hatchability, and yolk I content were monitored regularly throughout the 56 week study. With low dietary I (0–50 μg I/kg) and consequent low serum I, there is marked stimulation of thyroidal I uptake. Thyroidal stores of I and T 4 are reduced, but thyroidal T 3 and serum concentrations of both T 3 and T 4 are maintained. On dietary I regimes of 150–1200 gg I/kg, thyroidal I stores are regulated at essentially the same level despite a linear relationship between dietary I and serum I concentrations. Thyroidal hormone content and serum hormone concentrations also do not differ between dietary I regimes with >I50 μg I/kg. Egg production and egg hatchability are maintained on all dietary I intakes, a result consistent with the maintenance of serum T 3 and T 4 concentrations independent of dietary and serum I. In contrast to the thyroid, the ovaries do not appear able to regulate I in relation to I availability, and egg yolk I is proportional to serum I concentrations. These studies suggest that feed supplementation of 150 μg I/kg is sufficient to meet the needs of Japanese quail hens without requiring alterations in thyroid function. Quail adapt effectively to dietary I from 0–1200 μg I/kg; maintenance of thyroid status and egg production are favored while egg I stores vary with I availability.