Maternal dietary iodide influences turkey embryonic thyroid function

An experiment was designed to examine a mechanism to improve embryonic surv ival following maternal thyroid hormone manipulation. Commercial turkey bre eder 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 (T-4) co ncentrations in a time-dependent manner. Dietary iodide depressed maternal blood 3, 5, 3'-triiodothyronine (T-3) levels across all times examined. The maternal dietary treatment increased embryonic blood concentrations of T-4 at 25 to 28 d of incubation but depressed blood concentrations of T-3 only at 27 d of incubation. In a second trial, the same response was noted in m aternal blood when the hens were fed additional iodide with no correspondin g effects on T-3 concentrations. The iodide treatment decreased embryonic T -4 concentrations in the second trial as well but in a time-dependent manne r. Iodide accelerated the increase in T-4 concentrations coincidental with earlier pipping in eggs from iodide-fed dams compared with controls. The da ta indicate that the embryonic thyroid function during hatching is dependen t upon the maternal thyroid in turkey dams, even though the embryo develops outside the maternal body.