CORRELATIONS OF GENETIC-RESISTANCE OF CHICKENS TO MAREKS-DISEASE VIRUSES WITH VACCINATION PROTECTION AND INVIVO RESPONSE TO PHYTOHEMAGLUTININ

Twenty-three genetic groups of experimental and commercial meat and egg chickens were injected with moderately virulent BC-1 (exp 1) or highly virulent RB-1B (exp 2) Marek's disease (MD) virus. Birds of 7 genetic groups were divided into vaccinated and non-vaccinated groups and exposed by contact to the virulent RB-1B virus in exp 3. Response to phytohemaglutinin (PHA) injected in wing webs was measured in adult birds of all 23 groups (exp 4) to assess its relationship to MD resistance. There was a high correlation (0.8) between resistance of the genetic groups to the two viruses indicating that selection for resistance to one virus would be expected to improve resistance to the other virus. Regression of MD incidence in vaccinated birds on that in non-vaccinated birds resulted in regression coefficients of 0.41, 0.23, and 0.31% for males, females and combined sexes respectively, indicating that MD incidence increased linearly in vaccinated birds in relation to their genetic susceptibility to MD. Two significant correlations in males suggested that high swelling response to PHA may under some conditions be associated with MD resistance. However, the correlation coefficients were inconsistent and it was concluded that swelling response to PHA inoculated in the wing web is not predictive of MD resistance.