Studies of Resistance to Pullorum Disease in Chickens

RESISTANCE to disease is a variable factor. Operating together with changes in organism virulence, it is responsible for the severity of any given disease attack. Experimental evidence bringing more light to bear upon the conditions under which pullorum resistance varies may prove a valuable aid to brooding and flock management. Rettger, Kirkpatrick, and Stoneburn showed that pullorum resistance varies with age. Roberts and Card demonstrated the variation of pullorum resistance caused by genetic factors. These authors determined, among other things, that “Selection was effective in producing strains of domestic fowl more resistant than . . . unselected stocks in respect to infection by Salmonella pullora.” The same investigators also noted an increase of resistance under natural conditions in the presence of infection. They reported that among flocks of the Chia Gi variety in the vicinity of Peiping, China, pullorum reactors were present while no evidence of pullorum infection could be . . .