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Natural resistance to Marek's disease at hatching in chickens lacking maternal antibody, and relationship between this early resistance and resistance acquired with age.

Chickens of lines 6 and N, selected for resistance to Marek's disease (MD) and lacking maternal antibody, were resistant to MD mortality when exposed to pathogenic MD virus (MDV) at 1 day old. This finding indicated that natural resistance to MD is well developed at hatching in certain lines and is not dependent upon increasing age. Evidence obtained for lesion regression in early resistance and for possible genetic control of resistance acquired with age indicated that resistance at hatching and that acquired with age may be similar in character and may represent early and late manifestations of common natural resistance, possibly mediated through similar mechanisms.