Congenital Cervical Vertebral Malformations and Recurrent Bacterial Infections in Chickens Associated with In Ovo Vaccination Equipment Malfunction.

In ovo vaccination is an effective method of immunization that allows protection early in the life of the chick but requires precision during the administration. This present report describes an occurrence of cervical vertebral malformations in broiler chicks that coincide with mechanical failure of an in ovo vaccination system, in the absence of other detected infectious, nutritional, or toxic etiologies. Cervical scoliosis was observed in 2%-8% of chicks at hatch or within days post hatch in the affected flock, which all came from the same hatchery. Gross and histologic examination of eleven 30-day-old chickens revealed a cervical vertebral misalignment and fusion of the articular cartilage of adjacent vertebrae, with spinal cord compression, without evidence of inflammation. It is hypothesized that a malfunctioning in ovo vaccine injector with a bent needle might have caused mechanical trauma during the injection at day 18 of incubation, possibly contributing to the lesions observed in the chickens. Recurrent Enterococcus faecalis and Escherichia coli infections were also recorded in young chicks, a problem that persisted during the lifespan of the flock, possibly induced by compromised hygiene from the defective injector. These findings indicate that in ovo vaccination equipment malfunction could represent an underrecognized contributing factor to vertebral deformities in chicks.