Glucocorticoid administration during incubation: embryo mortality and posthatch growth in chickens

The effects of glucocorticoids (GC) on embryonic mortality and posthatch BW were studied. Cortisol hemisuccinate or corticosterone in 0.1-mL vehicles were injected into the albumen of 7-d-old White Leghorn chicken embryos. Embryonic mortality rates and the age after injection at which death occurred were determined. When 0.02 to 20 microg cortisol per egg were injected in saline, total embryonic mortality rate increased in a doseresponse manner, with a median lethal dose (LD50) at 10 microg. Saline injection alone caused a similar mortality rate to that caused by injection of 2 microg cortisol (around 35%). However, whereas mortality among the cortisol-treated embryos was greatest on Days 16 to 18, most of the saline-treated embryos died around the time of injection. The lethal effect of corticosterone, which is endogenous GC in adult chickens, was compared to that of cortisol by injecting both in the same vehicle (a saline:ethanol mixture) and was found to be similar. However, when 2, 10, or 20 microg of corticosterone was injected in oil, mortality rates were lower than those caused by the matching doses of cortisol in saline, probably due to the lower diffusion rate of the steroid out of the oil carrier. Hatch weight was significantly lower in chicks treated with 10 and 20 microg cortisol, and BW of the latter was lower compared with control throughout the 3-mo observation. In conclusion, cortisol and corticosterone are equally active in causing embryonic mortality. Posthatch BW is affected only by GC doses that are equal to or greater than the LD50.