Horses and donkeys are relatively resistant to tuberculosis caused by Mycobacterium tuberculosis complex (including Mycobacterium bovis) and Mycobacterium avium complex, and they are usually spillover hosts. Where TB has been controlled in cattle, only sporadic cases occur in equines.
When TB does develop in equids, granulomatous, noncalcified lesions are often found in the abdominal cavity, liver, and mesenteric lymph nodes, as well as the lungs and other sites. The main clinical sign is usually nonspecific wasting syndrome progressing to fever, dyspnea, and cough. The tuberculin test is not a reliable diagnostic assay in horses.