Lessons from the space experiment SL-J/FMPT/L7: the effect of microgravity on chicken embryogenesis and bone formation.

Thirty fertilized chicken eggs preincubated for 0, 7, and 10 days on earth (10 eggs each) were flown in the space shuttle "Endeavour" and further incubated for 7 days under microgravity. Twenty out of 30 eggs (nine out of ten 10-day-old eggs; 10 out of ten 7-day-old eggs; 1 out of ten 0-day-old eggs) were recovered alive after landing. The only living embryo of the 0-day-old egg died 24 days after launch, and was comparable to a 16-day-old embryo when it died. The high mortality of the 0-day-old eggs appeared to be related to the specific inner structure of the egg. The yolk (specific gravity, 1.029) would not have separated from the albumen (1.040) during space flight. The subtle difference in specific gravity between the yolk and the albumen appeared to play a critical role in early chick embryogenesis. All the tissues, including cartilage and bone, were formed normally in 7- and 10-day-old chicken embryos during space flight. When the 7- and 10-day-old embryos recovered at Kennedy Space Center (KSC) were further incubated on earth, they hatched normally. No appreciable changes were recognized in these chicks. The reason for these unexpected results is not known. Further space experiments are needed to explain the failure of the effects of microgravity on chicken embryogenesis.