EFFECT OF MATERNAL DIETARY TRIIODOTHYRONINE ON EMBRYONIC PHYSIOLOGY OF TURKEYS

The objective of the present experiment was to feed triiodothyronine (T3) to lines of turkey breeders selected for egg production and growth, and an unselected control line. The data were collected to determine a genetic basis for thyroid-mediated maternal effects on embryonic physiology and livability. At 30 wk of age, turkeys of the three lines were photostimulated and half of each line was fed a diet containing .5 ppm T3. Maternal dietary T3 increased egg weight, reduced yolk solids and eggshell conductance constants, and increased albumen solids and water in eggs in all lines compared with control eggs. Hatchability in all lines was not affected by the dietary treatment (Control = 72.2%; T3 treatment = 70.7%), but there was a significant interaction between dietary T3 and line of turkey for the time of embryonic mortality, time of hatching, and carbohydrate metabolism of the embryo. The T3 increased mortality of the Egg line and unselected line during pipping, increased mortality of the Growth line in the plateau stage, but decreased its mortality during internal pipping. Reduced glycogen in liver as well as a reduced gluconeogenesis were evident in embryos of the two selected lines fed T3. It is concluded that genetic lines may have different metabolic patterns based on their genetic constitution in order to compensate for variations in egg solids and eggshell conductance constants. The metabolic patterns are reflected in different levels of embryonic blood plasma glucose; glycogen, and gluconeogenesis.