Comparison of three experimental inactivated oil-emulsion Newcastle disease vaccines

White Leghorn pullets vaccinated previously with live Newcastle disease virus (NDV) were revaccinated at point-of-lay with 3 experimental oil-emulsion (OE) Newcastle disease vaccines to determine whether immunogenicity of OE vaccines is influenced by emulsion composition differences. The vaccines used were formulated differently but contained equal amounts of inactivated NDV in stable, low-viscosity, water-in-oil emulsions. Serological responses to the vaccines differed (P less than 0.01), but 55 of 56 OE vaccinates remained clinically normal following challenge exposure with viscerotropic velogenic NDV 28 or 44 weeks after revaccination; 4 of 21 nonrevaccinated controls and all of 20 nonvaccinated challenge controls were clinically affected or died.