A Test of Fowls Bred for Resistance to Lymphomatosis

INTRODUCTION FOUR years ago, Hutt et al. (1941) reported results for the first four generations of White Leghorns bred for resistance to disease, particularly to lymphomatosis. These showed that, whereas deaths from neoplasms during the test period were 16 percent in the unselected population with which the experiment started, in the fourth generation such deaths had been reduced to 12 percent. This decrease, really by a quarter of the original proportion, seemed significant, not merely because it was based on 785 birds, but because, at the same time, deaths from neoplasms were more than twice as frequent (26 percent) in the stock bred for susceptibility. Moreover, the decline of total mortality from 64 percent in the unselected population to 38 percent in the fourth generation permitted a higher proportion of the latter to develop neoplasms had they been genetically susceptible. The fact that only 12 percent did so is more . . .