Local reaction and serological response in commercial layer chickens injected intramuscularly in the leg with oil-adjuvanted Mycoplasma gallisepticum bacterin.

The incidence of local vaccine reaction was investigated in three flocks of commercial layer chickens after they were vaccinated intramuscularly in the leg with oil-adjuvanted Mycoplasma gallisepticum (MG) bacterin by commercial crews. Local vaccine reaction typically involved swelling due to a granulomatous cellulitis in the connective tissue above the tibiotarsal joint of the vaccinated leg. Histopathology revealed that the inflammatory reaction was confined primarily to subcutis and muscle fascia and rarely extended into muscle fibers, tendons, or tendon sheaths. Movement of the vaccinated flocks from growing to laying houses was associated with a significant increase in the incidence and severity of leg swelling. Antibodies against MG as measured by the hemagglutination-inhibition test were significantly higher in chickens with severe leg swelling than in chickens without leg swelling.