Exposure to Disease Agents of Strains of Chickens Differing in Resistance to Leucosis

THE development of a short-term test capable of differentiating families resistant and susceptible to leucosis has not yet been accomplished. At the Regional Poultry Research Laboratory (1944), no correlation was found between the incidence of lymphomatosis occuring under natural conditions among nine strains of White Leghorns and that experienced by these same strains when inoculated with lymphomatous material from either of two sources. By using subcutaneous inoculation with lymphomatous tissue, Heisdorf et al. (1947) were unable to differentiate, in a test period in which mortality was measured from 10 to 100 days of age, between a strain of White Leghorns selected for resistance to neoplasms and one selected for susceptibility. However, when chicks of these two strains were exposed to leucosis by placing lymphomatous material in their eyes, crops, and nostrils, the investigators were able to show consistent positive correlations at 100 and 225 days of age between mortality following . . .