Maternal Dietary Iodide Influences Turkey Embryo Thyroid Function

Abstract

An experiment was designed to discover a mechanism for improved embryonic survival resulting from supplemental maternal dietary iodine. Commercial turkey breeder hens were fed diets containing 4 ppm supplemental iodide during a 20 wk egg production period (32 to 48 wk of age). Dietary iodide treatment depressed maternal blood thyroxine (T₄) concentrations as the hens aged. Dietary iodide depressed maternal blood 3, 5, 3`- triiodothyronine (T₃) levels at all times examined. The dietary iodide 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 iodide treatment decreased embryonic T₄ concentrations as well but in a time-dependent manner. When the hens were similarly fed additional iodide in Trial 2, no effects were noted in T₃ concentrations. Iodide also accelerated the increase in embryo T₄ concentrations and initiated earlier pipping in embryos compared with non-supplemented controls. The data indicate that embryo thyroid function during hatching is affected by the maternal dietary iodide in turkey dams even though the embryo develops outside the maternal body.