Hematologic and semen quality changes in bulls with experimental eperythrozoon infection

Eperythrozoon organisms were isolated from the blood of a young beef bull with scrotal and hindlimb edema. Young beef bulls, managed under conditions closely mimicking those used in organized bull testing programs, were experimentally administered eperythrozoon organisms. Scant to few organisms were identified on blood smears from bulls (5 of 6) for 2 to 4 days starting 12 days after administration. After a second challenge with intravenously administered viable eperythrozoon organisms, the bulls demonstrated immunity by either failing to become parasitemic (4 of 6) or rapidly clearing the organisms from the blood (2 of 6). No bull became anemic, icteric, or hypoglycemic. Increased serum lactate and decreased blood bicarbonate concentrations probably reflected increased glycolytic activity of infected erythrocytes. A cause for azotemia observed late in the study was not determined. The bulls did not develop scrotal or hindlimb edema. Scrotal circumference and texture remained constant throughout the study. Semen quality was minimally altered while the bulls had organisms identified on blood smears. Harsh lung sounds were asculted in bulls during and immediately after organisms were present in the blood. Although the bulls reliably had organisms in the blood, none showed anemia, scrotal or hindlimb edema, or decreased semen quality; therefore, an additional factor or factors, or greater parasite load may be required for the expression of disease.