Long term effects of Marek's disease vaccination with cell-free herpesvirus of turkey and age at debeaking on performance and mortality of white leghorns.

Three-hundred-sixty, day-old Single Comb White Leghorn chicks were randomly placed in 8 treatment combinations. The combinations consisted of vaccinated or nonvaccinated chicks that were either not debeaked, or debeaked at day-old, 4 weeks old, or 8 weeks old. Vaccinated birds received 6,000 plaque forming units of cell-free herpesvirus of turkey vaccine per chick at day-old. Debeaking was performed by removing approximately two-thirds of the upper beak. Data were analyzed at the 5% level of probability. During the growing period (8 to 20 weeks of age), averag daily feed consumption per bird and feed efficiency for the vaccinated birds were not significantly different from those for the nonvaccinated. Regardless of the age at which debeaking was performed, the debeaked birds consumed significantly less feed and had superior feed efficiency than the nondebeaked birds. These traits were not significantly different among the various debeaked groups. Vaccination, or debeaking, or age at debeaking did not significantly influence mortality during the growing period. During the laying period (20 to 84 weeks), a significantly higher percentage of extra large eggs and a significantly lower percentage of medium eggs were collected from the vaccinated birds in comparison to those collected from the nonvaccinated. Also, average egg weight for the vaccinated birds was significantly heavier than that for the nonvaccinated. Debeaking at either 4 weeks or at 9 weeks of age caused a significant reduction in egg weight. Vaccination, or debeaking, or age at debeaking did not significantly influence hen-day egg production. Feed efficiency between the vaccinated and the nonvaccinated birds was not significantly different. Debeaking tended to improve feed efficiency. Vaccination as well as day-old debeaking significantly reduced laying house mortality. Debeaking the birds either at 4 weeks or at 8 weeks of age reduced laying house mortality numerically.