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Abstract
Infectious Bronchitis Virus (IBV), a gammacoronavirus of chickens, is considered a respiratory disease virus. Some strains of IBV cause reproductive disease, such as decreased egg quality and production. IBV has also been associated with False Layer Syndrome, characterized by large, fluid-filled cysts in the oviduct of laying hens that cannot lay eggs. These hens appear otherwise normal, making early diagnosis difficult. Known IBV strains associated with False Layer Syndrome include the QX, Massachusetts, and Australian T strains. In the last decade, IBV variant DMV/1639 has been isolated from field cases of False Layer Syndrome. Our research aimed to characterize the role and prevention of DMV/1639 in the development of cystic oviduct and False Layer Syndrome. Groups of SPF pullets were challenged with either DMV/1639 or M41 (positive control) at 3-, 7-, or 14-days of age and monitored for gross and histopathological reproductive lesions. Our results indicated that IBV DMV/1639 can cause cystic oviducts that will lead to False Layer Syndrome and a younger age at challenge yields a higher prevalence and severity of cystic oviduct. Our second study evaluated the role of vaccination on development of cystic oviduct caused by DMV/1639. Based on the gross and histological lesions in vaccinated and unvaccinated SPF birds challenged at 7-days of age with DMV/1639, there did not appear to be a relationship between vaccination strain or timing of administration and the development of cystic oviduct, indicating that incidence of False Layer Syndrome is not just dependent on age at infection or vaccination status. Because SPF pullets do not have maternal antibodies against IBV, we investigated the role of maternal antibodies in the development of cystic oviducts in a third study. From this study, there appears to be a pattern between maternal antibody-positive birds and lower incidence of cystic oviduct. Overall, our results indicate that the development of False Layer Syndrome caused by IBV DMV/1639 is multifactorial, influenced by age at infection, vaccination status, and maternal antibody status. Prevention of loss due to False Layer Syndrome should include a combination of biosecurity, efficient layer breeder vaccination, and vaccination at hatch for layer pullets.