heaves, chronic pulmonary emphysema in horses. Heaves is characterized by the disruption of normal lung tissue with resultant loss of the lung's elastic recoil. A forced expiratory effort is needed to empty the lungs of air. The cause is not known, but the disease is associated with prolonged feeding of poor-quality roughage and dusty feeds. These conditions may incite an allergic reaction in association with chronic bronchitis, thus leading to emphysema. Treatment consists of substituting dampened hay and grain or pelleted rations for the dusty feeds and administering anti-inflammatory drugs. Complete recovery is rare.

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