Onset of the humoral immune response of layer chicks vaccinated in ovo with strain F Mycoplasma gallisepticum vaccine and evidence of male-biased mortality12

Previous trials in which layers were in ovo - vaccinated against strain F Mycoplasma gallisepticum ( FMG ) showed that nearly 50% of the birds produced IgM antibody against FMG at 6 wk of age ( WOA ). Standard FMG vaccination application at 9 or 10 woa, result in this percentage at approximately 15 woa. This study investigated when FMG in ovo-vaccinated birds initiate a humoral immune response prior to 6 wk, and if sex influences this response. Hy-Line W-36 embryonated eggs were either not vaccinated (controls) or in-ovo vaccinated with a 50 µL volume of a 10 −6 dilution of Poulvac MycoF vaccine (Zoetis). For each treatment group, 384 straight-run chicks were reared. At hatch and at 2, 3, 5, 7, 14, 21, and 28 d post-hatch, 54 birds per treatment were individually weighed and a blood sample was collected for Mycoplasma gallisepticum ( MG ) IgM antibody detection. ELISA was run on blood samples at 14, 21, and 28 d to distinguish IgG antibody production. At each age, BW was not different between vaccinated and control chicks (all P > 0.19). Males, however, outweighed females starting at d 5 ( P = 0.02). Mortality was 1.0% for the control birds and 12.2% for the FMG birds during the first 2 wk. The majority (72.3%) of the mortalities in the FMG group were male. The percentage of control and FMG in ovo-vaccinated birds with IgM antibody production was 0% and 1.9% on d 7, 0% and 31.5% on d 14, 1.9% and 55.9% on d 21, and 0% and 60.6% on d 28, respectively. IgG antibody production in the FMG in ovo-vaccinated birds was 0.0% at 14 d, 2.9% at 21 d, and 21.2% at 28 d of age. All control birds tested negative for FMG-IgG production. In conclusion, the earliest detection of MG antibodies after in ovo vaccination with live FMG occurred at 7 d. Male layer chickens were more susceptible to the effects of an in ovo FMG vaccine than females.