Resistance of strains of chickens to Marek's disease

Fifteen strains of chickens were tested in three experiments for susceptibility to Marek’s disease (MD). Highly significant differences among strains and between sexes were observed for both mortality (two experiments) and total incidence (three experiments). Correlation between ranking of replicated strains for MD incidence in two experiments was significant for females and for sexes pooled but not for males. There was a significant correlation between ranking of strains exposed by contact in a controlled environment house (based on incidence of MD) with ranking of strains in a 147-day test at a field station (based on total mortality or mortality with lymphoid tumors). Cornell S strain was included in comparisons with nine other strains and was the most susceptible to MD. The Cornell K strain was significantly more resistant than two of nine strains and was significantly more susceptible than four strains.