Acute lethality and recovery of goats after 1 MVp X-irradiation

The ${\rm LD}_{50/60}$ and recovery pattern after a sublethal radiation exposure have been determined for the Angora goat, exposed to 1 MVp x-rays at 450 R/hour. The ${\rm LD}_{50/60}$ was 327 R (95% confidence interval: 292-378). The split-dose technique was utilized for measurement of the amount of recovery from the initial conditioning exposure of 150 R. At 7 days, minimal recovery had taken place, as 84% of the initial injury remained. By 14 days, rapid recovery had occurred and the animals' LD50 had returned to normal. At 21 days, 16% of the initial injury remained. At 30 days, the animals exhibited a reversion in radiosensitivity to the extent that the injury present at that time appeared to be greater than that produced by the conditioning exposure. The recovery pattern in the goat is marked by three distinct phases and does not fit a simple linear or exponential pattern. Routine hematological sampling for 160 days after 150 R, while showing definite depression of the leukocytes and very slow recovery of the mononuclear cells, showed no correlation between changes in the peripheral blood elements and the animals' recovery pattern.