Incubation temperature affects plasma insulin-like growth factors in embryos from selected lines of turkeys

An experiment was conducted to test the hypothesis that incubator temperature may affect circulating insulin-like growth factors (IGF-I and IGF-II). In prior studies, growth of turkey embryos was altered by increasing incubator temperatures. Interestingly, the embryonic growth of a growth-selected line (F) was reduced, whereas embryos from an egg-production-selected line (E) did not alter embryonic growth but altered organogenesis. Growth of the F and E lines was altered experimentally in the current study by increasing incubator temperature from 36.8 to 37.2 C during the last 3 d of incubation. Embryonic blood samples were taken and analyzed for glucose, glucagon, IGF-I, and IGF-II concentrations. Increased incubator temperature elevated embryonic plasma glucose concentrations of all treatments compared to controls, which was accompanied by increased plasma glucagon concentration only in the E line embryos. Line and treatment interacted to affect IGF-I and IGF-II concentrations of embryo and hatchlings. Line E embryos increased IGF-I in response to the higher temperature, but controls did not; F embryos altered IGF-II in response to treatment, but controls did not. Alterations in IGF-I in E corresponded to growth responses, whereas IGF-II in F corresponded to metabolic responses. We concluded that changes in turkey embryo growth rates to incubator temperature involved changes in IGF-I. Additionally, IGF-II and glucagon are involved in intermediary metabolism during higher temperature exposure.