RESISTANCE TO MAREKS-DISEASE ASSOCIATED WITH B21-LIKE HAPLOTYPES

A total of 4595 chickens representing a total of 25 MHC haplotypes wer e hit by a spontaneous, particularly violent outbreak of Marek's Disea se early in rearing. Among the chickens of 6 different families in whi ch B21 or B21-like haplotypes were segregating, the overall mortality at 52 weeks of age were between 74% and 96% compared to 100% in a fami ly where no protective haplotypes were present. The overall survival i n the former 6 families was also significantly correlated to the prese nce of B21 or B21-like haplotypes. In two families carrying either the classical B21 or a B21 like haplotype (B(W1)) from Red Jungle Fowl, b ut having 94% common non-MHC background genes of White Leghorn origin, 29% of the chickens having the B(W1) haplotype survived compared to 1 8% of the B21 chickens. The superiority of the B(W1) chickens was stil l more pronounced in comparison with chickens of 50% meat-type origin, although these were also carrying B21 or B21-like haplotypes.