Effects of sampling location and frequency on the detection of Mycoplasma gallisepticum populations in the respiratory tract of commercial layer pullets

Authors: SASIDHARAN, S - Mississippi State University; Collins Elliott, Katie; Evans, Jeffrey; Read, Quentin; PEEBLES, E - Mississippi State University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2026
Publication Date: 6/17/2026
Citation: Sasidharan, S.K., Collins Elliott, K.E., Evans, J.D., Read, Q.D., Peebles, E.D. 2026. Effects of sampling location and frequency on the detection of Mycoplasma gallisepticum populations in the respiratory tract of commercial layer pullets. Poultry Science. 105: 107277. https://doi.org/10.1016/j.psj.2026.107277.
DOI: https://doi.org/10.1016/j.psj.2026.107277

Interpretive Summary: Mycoplasma gallisepticum (MG) is a bacteria that is endemic in commercial laying hen facilities due to the need for different aged birds to be present on the same farm. In other words, the younger birds catch MG from the older birds. MG infections predominantly impact egg production and the main tool to combat the reduced egg production is vaccination, with live vaccines being particularly effective. Overlay programs (using different vaccine strains of MG at different times during the production of a flock) may be utilized but the impact of how MG populations change in the bird from these vaccines and from field strains of MG is unknown. The main location of MG colonization within the bird is the trachea, with the choanal cleft being found as a less invasive location to swab that is indicative of tracheal colonization. In a first step toward determining how MG strain populations may change during the life of a commercial laying hen, it is needed to know how simply swabbing the bird in the trachea or the choanal cleft may impact MG populations. Swab samples will be needed in order to detect what MG strains and in what abundance are present within the bird. Thus, this current study was conducted taking 80 laying hens at 11 wk of age and infecting them with the F strain (a vaccine strain) of MG. After 2 weeks following infection with MG, the birds were assigned a timing of swabbing either every 2 days, every 4, 8, or 16 days between swabbings. The trachea and the choanal cleft were each swabbed at each swabbing event. The quantity of F strain MG present in each swab sample was distinguished using PCR. It was found that there was no difference in the amount of MG DNA detected regardless of the swabbing frequency. There was a greater amount of MG detected in the choanal cleft though in comparison to the tracheal swabs. This information will now allow researchers to be able to test how MG strains change over time within laying hens to better combat the bacteria. Researcher's can swab at any frequency with no impact to the overall MG populations.

Technical Abstract: Mycoplasma gallisepticum (MG) is an economically important pathogen in layers, as it is responsible for chronic respiratory disease. Routine detection of MG is performed via swabbing of the trachea or choanal cleft. However, the possible impact of repeated sampling events on in vivo MG population dynamics within individual subjects has not been investigated. Therefore, eighty 11 wk-old Hy-Line W-36 layer pullets were infected with F-strain MG, and were individually caged in one of 4 identical rooms, with 20 birds per room. Two wk post-infection, 5 birds in each room were randomly assigned to either 2, 4, 8, or 16 d sampling interval schedules, and were maintained for an additional 32 d. At each sampling event, the birds were swabbed in the choanal cleft and trachea, and sample-associated MG populations were quantified using real-time PCR. A complete block experimental design was employed, with room as an experimental block containing multiple replicates of each sampling schedule. Data, within birds, was subjected to repeated measures analysis. Undetected bacterial populations were considered as a negative sample. There was no evidence of any difference in probability of detecting a positive sample or in trend over time of microbial abundance due to the different sampling schedules. However, there were ~26 times as many genomic equivalents of MG in the choanal cleft than in the trachea across all the sampling intervals, and significantly greater probability of positivity in the choanal cleft at d 16 and d 32. It was concluded that the site of sampling influenced MG population with the sampling interval exerting no additional influence.