Influence of diet-mediated maternal thyroid alterations on hatchability and metabolism of turkey embryos

Large White turkey breeder hens from a strain exhibiting poor hatchability were fed thyroid-altering diets. The following dietary treatments were fed to randomized groups of hens for 15 wk of egg laying: 1) 16.5% protein turkey breeder diet (control), 2) the control diet containing 2.1 ppm supplemental iodine, 3) the control diet containing .1% thiouracil, and 4) the control diet containing .5 ppm triiodothyronine (T3). Blood samples were taken from hatching embryos from hens fed each diet. Embryonic hearts and livers were weighted prior to and during pipping as well as after hatching. Blood plasma was analyzed for thyroxine (T4), T3, and glucose. Livers were assayed for glucose-6-phosphatase activity. Supplemental maternal dietary iodine elevated embryonic T4 concentrations prior to pipping. Dietary T3 and iodine increased hepatic glucose-6-phosphatase activity and blood plasma glucose concentration prior to pipping. Feeding thiouracil increased embryonic liver weights but decreased heart and body weights. Blood plasma T4 was elevated in embryos from hens fed thiouracil but blood glucose levels were depressed because of a lack of increased glucose-6-phosphatase activity. Feeding iodine decreased the enzyme activity at internal pipping. It is suggested from the data that maternal thyroid metabolism may influence hatchability via embryonic thyroid and carbohydrate metabolism during hatching.