Effect of continuous gamma irradiation of chick embryos upon hatchability and growth

One hundred and twenty fertile White Leghorn eggs were continuously exposed to gamma rays $({}^{60}{\rm Co})$ during incubation at each of the following rates: 3.4, 1.8, 1.0, 0.9, 0.5, and 0.3 R/hour for 20 days. They were then hatched with the control eggs and hatchability and growth rate determined. Hatchability was reduced at 0.9 R/hour or higher. The irradiated embryos appeared to be weaker as evidenced by an increased number of pipped eggs that didn't hatch and longer hatching times. No differences in body weight between irradiated and control chicks were apparent at hatching. The control birds were heavier at 2, 4, and 16 weeks of age than the chickens which received 1.8 R/hour or more as embryos. At these same ages, those receiving 3.4 R/hour as embryos were lighter in weight than any of the other groups. Subsequent 60 Co irradiation studies of 4-week-old cockerels which received 3.4 R/hour as embryos revealed an increase in mortality which suggested a residual nonrepaired damage existed from the embryonic irradiation.