Prediction of the occurrence of Marek's disease in chickens on the basis of the quantitation of cell-mediated immunity.

Cell mediated immunity was assayed in chickens on the basis of the dinitrochlorobenzene skin test, T lymphocyte numbers in peripheral blood and the graft-versus-host reaction. It was found that chickens that were to develop clinical Marek's disease following exposure to Marek's disease virus had significantly lower prechallenge levels of cell mediated immunity than those that were resistant to Marek's disease. The graft-versus-host reaction had a smaller coefficient of variation than the other two tests, and it was concluded that this test is likely to be the most reliable indicator of the outcome of infection with Marek's disease virus.