Myeloid and Megakaryocytic Bone Marrow Hypoplasia

Johanna L. Watson • Gary P. Carlson

Myeloid and megakaryocytic bone marrow hypoplasia has been reported in eight young Standardbred horses sired by the same stallion.¹⁷ Clinical signs were variable and in some individual horses included nonhealing wounds, unresponsive fevers, pleuritis, pneumonia, ataxia, hemoperitoneum, and bleeding into the bowel. Seven of eight horses died or were euthanized. The principal laboratory findings were a variable red cell count from normal to modest to marked anemia, moderate to profound neutropenia, and intermittent thrombocytopenia in most of the horses. There appeared to be a cyclic variation in neutrophil and platelet counts. A familial basis for the disease is suspected.¹⁷