Induction of eggshell apex abnormalities by Mycoplasma synoviae: field and experimental studies

A novel eggshell pathology, characterized by an altered shell surface, thinning, increased translucency, and cracks and breaks in the eggshell apex, has become increasingly common in layer flocks of various breeds in The Netherlands. Two field studies found an association between the eggshell apex abnormalities (EAA) and infection with Mycoplasma synoviae. M. synoviae was isolated from the oviduct of birds that produced abnormal eggs, but not from birds in control flocks, although both affected and control birds had agglutinating antibodies against M. synoviae. After a single injection with long-acting oxytetracycline, the production of abnormal eggs ceased, but then reoccurred about 12 days later. A causal relationship between EAA and M. synoviae infection was subsequently demonstrated experimentally. EAA occurred after intratracheal inoculation of birds with M. synoviae, and even more frequently in birds infected with infectious bronchitis virus 5 days before inoculation of M. synoviae. EAA also occurred, although less frequently, in birds inoculated intravenously with M. synoviae and infected with infectious bronchitis virus. EAA did not occur in birds only inoculated intravenously with M. synoviae. M. synoviae was only isolated from the oviducts of birds producing abnormal eggs. The mean daily egg production was reduced in all groups infected with M. synoviae. Examination of the eggshells by scanning electron microscopy revealed that the mammillary layer of the calcified zone was absent and that the inner eggshell membranes were thicker. Isolates of M. synoviae from the oviducts of birds from farms producing abnormal eggs were examined by amplified fragment-length polymorphism analysis and did not appear to be clonal.