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

Authors: Collins Elliott, Katie; BRANTON, SCOTT - Retired ARS Employee; Evans, Jeffrey - Jeff; Magee, Christopher; PEEBLES, E - Mississippi State University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2022
Publication Date: 1/30/2022
Citation: Collins Elliott, K.E., Branton, S.L., Evans, J.D., Magee, C.L., Peebles, E.D. 2022. Onset of the humoral immune response of layer chicks vaccinated in ovo with strain F Mycoplasma gallisepticum vaccine and evidence of male-biased mortality. Poultry Science. 101:101761. https://doi.org/10.1016/j.psj.2022.101761.
DOI: https://doi.org/10.1016/j.psj.2022.101761

Interpretive Summary: Mycoplasma gallisepticum (MG) is a bacterium that can cause respiratory disease in poultry and other bird species. This bacterium is adept at evading the immune system of the bird and is never fully cleared from the bird once the bird is infected. Once a bird contracts MG, the bird has MG for life. The broiler or meat-type chicken industry has been able to eradicate MG from their flocks due to the short life span and “all-in-all-out” capabilities of broiler houses. Commercial layer houses, however, are consistently stocked with long-lived birds of varying ages producing infertile table eggs for human consumption. Thus, once a commercial laying chicken farm contracts MG, the producer must live with MG. To combat the effects of MG, which also negatively impacts egg production, egg producers may vaccinate their birds. There are several MG vaccines available including a popular vaccine Poulvac MycoF vaccine manufactured by Zoetis (FMG). This experiment continues work evaluating giving the FMG vaccine to the commercial layer chicken by in ovo route (before the chicken hatches from the egg). This vaccine is usually given around 9 or 10 weeks of age which is relatively near the age when layer chickens will begin laying eggs (approximately 18 weeks of age). It has been shown that chickens have sufficient initial antibody production (IgM) 6 weeks after being vaccinated (at approximately 15 weeks of age). Beginning to lay eggs can be a stressful period for a chicken, so previous work giving the vaccine in ovo was researched to evaluate if giving the FMG much earlier in the bird’s life would be beneficial to the bird’s health and to egg production. Previous in ovo FMG research found that birds have produced IgM antibodies at 6 weeks of age but when these antibodies began to appear has been unknown. This current study evaluated when exactly the onset of antibody production occurs. Birds were either non-vaccinated controls or given the FMG vaccine in ovo and allowed to hatch. Once the birds hatched, they were raised in 2 replicate separate rooms consisting of 384 straight-run chicks (males and females) per each treatment. 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. Once birds were bled, they were removed from the study. ELISA was also tested on blood samples at 14, 21, and 28 d to distinguish IgG antibody production (an antibody type produced after the initial IgM antibody production). Any birds that died in the trial were opened to determine the sex of the bird and all sample birds were also sexed. Normally only females are raised because a male is not necessary for infertile table egg production. There is evidence that male birds are more susceptible to MG, however, this has never been proven in a domestic bird species like a chicken. The study found that the earliest IgM antibody production in response to in ovo FMG vaccination was found in one bird at 7 days of age. Percentages of IgM positive birds continued to increase particularly in the 2nd and 3rd week post-hatch and reached the same percentage as the previous trials that tested birds at 6 weeks at 3 weeks of age. Thus, the IgM antibody response met the 6-week level 3 weeks earlier. The percentage of birds with IgG antibody production reached a maximum of 21.2% of the birds at 4 weeks of age showing IgG antibody production. This percentage had not yet reached the percentages of birds that exhibited IgG antibody production observed in birds at 6 weeks post-hatch in previous studies. One interesting finding of the study was that more male chicks than female chicks died early due to the in ovo vaccination of FMG. No evidence was found to indicate that females were more likely to produce antibodies or have gr

Technical Abstract: 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.