Early growth rates and their relationships to mortalities of five breeds of chickens following exposure to acute gamma radiation stress.

Growth and mortality responses were recorded for 541 chicks, representing five different breeds of chickens, following acute exposures to gamma radiation stress at two days of age. Although there were no statistically significant differences in the LD50/30 of the five breeds studied, Cobb broilers showed the highest (1580R) and White Leghorn bantams the lowest (980R) levels, respectively. Other breeds studied included the standard White Leghorn, Athens Randombreds and a strain of feral bantam. Growth rates of body weights were proportionately more depressed by radiation stress than were body sizes, as measured by the lengths of the culmen, tarsus, middle toe and longest primary wing feather of all 32 day-old survivors. Among these structures, the length of the culmen seemed to be the least affected by radiation stress in all of the breeds studied. Feral bantams were able to tolerate the greatest depression in weight gain before exhibiting mortality at exposures below their LD50/30' while Cobb broilers tolerated the greatest depression of weight gain at higher exposure levels. There was a suggestion that those characteristics which were strongly selected for in the course of a particular breed's development were those which experienced the greatest proportional depressions following exposure to gamma radiation stress.