As part of a long-term study of the effects of irradiation during development, prenatal and early neonatal mortality were evaluated for beagles exposed in utero at 8 days postcoitus (dpc), 28 dpc, 55 dpc, or 2 days postpartum. Mean doses used were 0, 0.16, or 0.83 Gy. A decrease in whelping rates was observed for female breeders irradiated at 8 dpc. There was a significant decrease in litter sizes from female breeders irradiated at 8 and 28 dpc. Both of these findings are indicative of increased embryonic mortality. There was a significant decrease in the percentage of females born after exposures given at 28 dpc, indicating a differential radiosensitivity by sex. A significant increase in early neonatal mortality up to 14 days of age was observed for beagles exposed 8 or 28 dpc, again with an excess mortality in females.

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