Improving the outcome of a Marek's disease challenge in multiple lines of egg type chickens.

A challenge test following inoculation with a standard amount of a vv+ strain of the Marek's disease (MD) virus in multiple lines and multiple generations of egg type chicken and the corresponding phenotypic trend are described. This program significantly reduced mortality of progeny from selected sires for three to 11 generations in eight of the nine elite lines studied herein. In brown egg lines, a retrospective analysis of DNA indicated an association between the blood type B (major histocompatibility complex) of the sire and the MD mortality in the challenge of its progeny. As a result of the multigeneration stock amplification and crossbreeding processes used in the commercial breeding industry, improvement in survival after challenge at the elite level will translate to improved welfare for millions of birds at the commercial production level.