Maternal dietary iodide influences turkey embryonic thyroid function.

An experiment was designed to examine a mechanism to improve embryonic survival following maternal thyroid hormone manipulation. Commercial turkey breeder hens were fed diets containing supplemental iodide to mimic changes in the maternal thyroid output during an egg production cycle (32 to 48 wk of age). Dietary iodide treatment depressed maternal blood thyroxine (T4) concentrations in a time-dependent manner. Dietary iodide depressed maternal blood 3, 5, 3'-triiodothyronine (T3) levels across all times examined. The maternal dietary treatment increased embryonic blood concentrations of T4 at 25 to 28 d of incubation but depressed blood concentrations of T3 only at 27 d of incubation. In a second trial, the same response was noted in maternal blood when the hens were fed additional iodide with no corresponding effects on T3 concentrations. The iodide treatment decreased embryonic T4 concentrations in the second trial as well but in a time-dependent manner. Iodide accelerated the increase in T4 concentrations coincidental with earlier pipping in eggs from iodide-fed dams compared with controls. The data indicate that the embryonic thyroid function during hatching is dependent upon the maternal thyroid in turkey dams, even though the embryo develops outside the maternal body.