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In chickens and turkeys, a bursa lined with
synovial membrane normally exists over the anterior projection of the keel
bone. When this bursa becomes inflamed by trauma or infection, fluid or
exudate accumulates and appears as a fluid-filled blister 1-3 cm in
diameter.  Causes of
trauma to this bursa include poor feathering, hard flooring, and leg
weakness, which is associated with increased recumbency. Some young
turkeys have pointed keels, which can lead to increased bursal trauma, but
as the size of their breast muscle increases and trauma decreases, lesions
may regress. Infectious causes of sternal bursitis include
Mycoplasma synoviae , Staphylococcus , and
Pasteurella spp .
Breast buttons are lesions in a similar location that have a hard crust on the surface and a core of dead skin and granulomatous reaction extending into the subjacent subcutis. They are not due to the causes listed above for breast blisters but may be chemical burns due to prolonged contact of poorly feathered skin with wet litter containing ammonia or toxins.
See Also:
Ascites Syndrome
Cannibalism
Fluke Infections
Gout
Pendulous Crop
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