Courtesy of Dr. Jean Sander.
Chickens and turkeys have a synovial membrane in the subcutis on the ventral and anterior aspects of the keel bone, known as the sternal bursa or keel bursa. When this bursa becomes inflamed by trauma or infection, fluid accumulates and appears as a fluid-filled blister 1–3 cm in diameter. Factors in trauma to the bursa include poor feathering, hard flooring, and leg weakness, which is associated with increased time of sitting on the keel (sternum). Coarse bedding materials or wet litter conditions are predisposing factors and should be corrected when identified. Infectious causes of sternal bursitis include Mycoplasma synoviae, Staphylococcus, and Pasteurella spp, either from local trauma (Staphylococcus) or as an extension of a systemic infection.
