Maternal Thyroid Hormones in Japanese Quail Eggs and Their Influence on Embryonic Development

We addressed the relationship between the thyroid status of hens and the thyroid hormone content of their eggs, as well as the influences of egg hormones on embryonic development. Methods for measuring thyroid hormones in egg yolk were verified by demonstrating consistency in the recovery of yolk thyroid hormones following a methanol/chloroform extraction and in the measurement of thyroid hormones by RIA for a range of hormone concentrations in yolk extracts. Untreated hens produced eggs with yolk thyroxine (T4) concentrations that were low relative to plasma T4, but yolk triiodothyronine (T3) concentrations comparable to those of plasma. Hens dosed twice daily with T4(1 or 3× the daily thyroid secretion rate, TSR, of T4per dose) had significantly higher plasma and egg yolk T4concentrations than did control hens dosed with saline. In general, the T4concentration of egg yolk varied with the thyroid status of the hen. When the relationship between each hen's plasma T4and the yolk T4concentration of her eggs was examined, hens appeared to regulate T4deposition into yolk at “levels” characteristic of the “levels” of thyroid status produced by the different doses of T4. Embryonic pelvic cartilage, a thyroid hormone-responsive tissue, showed enhanced growth and differentiation in embryos from eggs of hens given the highest dose of T4. Specifically, alkaline phosphatase activity (a marker of differentiation) and pelvic cartilage wet and dry weights were significantly greater in embryos from high T4eggs (hens on the 3× TSR dose) than those in controls. However, embryos from high T4eggs did not differ in general body growth (body weight, length, and general morphology) or hatchability compared to controls. In a single T3experiment, hens were dosed twice daily with 1 μg T3. The embryos from eggs of these hens had accelerated differentiation/maturation of pelvic cartilages (sampled at Day 12) compared to those from control eggs; body growth did not differ from that of controls.