Optimization of hydrophile-lipophile balance for improved efficacy of Newcastle disease and avian influenza oil-emulsion vaccines.

Preparations of inactivated Newcastle disease (ND) and avian influenza (AI) oil-emulsion vaccines with surfactant hydrophile-lipophile-balance (HLB) values between 4.3 and 9.5 were evaluated for their efficacy in broiler-type white rock chickens. Chickens were vaccinated at 3-4 weeks of age and bled at 2-week intervals over 8 weeks. Post-vaccinal hemagglutination-inhibition (HI) geometric mean titers (reciprocals) ranged from 197 to 485 for ND vaccines and from 184 to 1040 for AI vaccines. Based on the HI response, an HLB value of 7.0 induced the greatest stimulation of antibody titers. Ten percent surfactant in the oil phase of the vaccines induced maximum titers at this HLB. The oil:aqueous ratios of the vaccines did not greatly influence the overall serologic response when the vaccines had an HLB of 7.0. These results indicate that manipulating surfactant HLB values of OE vaccine may maximize the HI response in broilers.