Genetic Control of Susceptibility to the Avian Leukosis Complex

Abstract

Three inbred lines of White Leghorns were crossed in all combinations giving nine mating types which were exposed to Marek’s disease (MD) by natural and artificial means. Ranking of the mating types by MD mortality after artificial exposure to either the JM or the GA isolate was similar to the ranking after natural exposure, suggesting that exposure to either isolate would be effective in increasing mortality for selection of lines resistant to naturally occurring disease. Differences in the response pattern between inoculation and contact exposure to either isolate was noted. This observation, the large maternal effects and the changes in dominance due to method of exposure, indicate that cross performance cannot be predicted from pureline performance, and that each cross should be evaluated under several conditions of exposure.