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. Em bryonic mortality rates and the age after injection at which death occurred were determined. When 0.02 to 20 mug cortisol per egg were injected in sal ine, total embryonic mortality rate increased in a dose-response manner, wi th a median lethal dose (LD50) at 10 mug. Saline injection alone caused a s imilar mortality rate to that caused by injection of 2 mug cortisol (around 35%). However, whereas mortality among the cortisol-treated embryos was gr eatest on Days 16 to 18, most of the saline-treated embryos died around the time of injection. The lethal effect of corticosterone, which is endogenou s 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 mug of corticosterone was injected in oil, mort ality 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 t he oil carrier. Hatch weight was significantly lower in chicks treated with 10 and 20 mug cortisol, and BW of the latter was lower compared with contr ol throughout the 3-mo observation. In conclusion, cortisol and corticoster one are equally active in causing embryonic mortality. Posthatch BW is affe cted only by GC doses that are equal to or greater than the LD50.