Effect of Intravenous Administration of Cobalt Chloride to Horses on Clinical and Hemodynamic Variables

Background: Cobalt chloride (CoCl₂ ) is administered to racehorses to enhance performance. The purpose of this study was to evaluate the clinical, cardiovascular, and endocrine effects of parenterally administered CoCl₂ .

Objectives: To describe the effects of weekly intravenous doses of CoCl₂ on Standardbred horses.

Animals: Five, healthy Standardbred mares.

Methods: Prospective, randomized, experimental dose-escalation pilot. Five Standardbred mares were assigned to receive 1 of 5 doses of CoCl₂ (4, 2, 1, 0.5, or 0.25 mg/kg) weekly IV for 5 weeks. Physical examination, blood pressure, cardiac output, and electrocardiography (ECG) were evaluated for 4 hours after administration of the first and fifth doses. Blood and urine samples were collected for evaluation of cobalt concentration, CBC and clinical chemistry, and hormone concentrations.

Results: All mares displayed pawing, nostril flaring, muscle tremors, and straining after CoCl₂ infusion. Mares receiving 4, 2, or 1 mg/kg doses developed tachycardia after dosing (HR 60-126 bpm). Ventricular tachycardia was noted for 10 minutes after administration of the 4 mg/kg dose. Increases in systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP) occurred after administration of all doses (4, 2, 1, 0.5, and 0.25 mg/kg). Profound hypertension was observed after the 4 mg/kg dose (SAP/DAP, MAP [mmHg] = 291-300/163-213, 218-279). Hemodynamics normalized by 1-2 hours after administration. ACTH and cortisol concentrations increased within 30 minutes of administration of all CoCl₂ doses, and cardiac troponin I concentration increased after administration of the 4 and 2 mg/kg doses.

Conclusions and clinical importance: The degree of hypertension and arrhythmia observed after IV CoCl₂ administration raises animal welfare and human safety concerns.