The effect of Marek's disease vaccination on the immunisation of day‐old chicks against Newcastle disease, using B1 and oil emulsion vaccine

Concurrent vaccination of one-day-old chicks with 2 x 10(5) 50% embryo infectious doses of live B1 Newcastle disease virus and 0.25 ml killed oil emulsion Newcastle disease vaccine produced satisfactory levels of circulating haemagglutination inhibiting antibody although the recipient chicks possessed titres of maternally derived antibody as high as 10 log(2). This effect was also seen when the chicks were given turkey herpesvirus for immunisation against Marek's disease. The satisfactory Newcastle disease antibody levels achieved by the vaccination programme did not fall below 5 log(2) during the first 20 weeks of the birds' 40 week life span. Re-vaccination with live B1 vaccine at 17-days-old did not boost antibody levels, but re-vaccination with oil emulsion vaccine at 9 weeks-old produced a rise from 7 log(2) to 11 log(2). These findings are considered to be significant in establishing and maintaining immunity to Newcastle disease for both broilers and laying hens, particularly in areas where the disease is endemic.