Cobalt is an essential trace element for many vital physiological functions. Cobalt is also known to stabilise hypoxia-inducible transcription factors leading to increased expression of erythropoietin which activates production of red blood cells. This implies that cobalt can be used to enhance aerobic performance in racing horses. If this becomes a pervasive practice, the welfare of racing animals would be at risk because cobalt is associated with cardiovascular, haematological, thyroid gland and reproductive toxicity as observed in laboratory animals and humans. It is expected that similar effects may manifest in horses but direct evidence on equine specific effects of cobalt and the corresponding exposure conditions leading to such effects is lacking. Available pharmacokinetic data demonstrates that intravenously administered cobalt has a long elimination half-life (42-156 h) and a large volume of distribution (0.94 L/kg) in a horse implying that repeated administration of cobalt would accumulate in tissues over time attaining equilibrium after ~9-33 days. Based on these pharmacokinetic data and surveys of horses post racing, threshold cobalt concentrations of 2-10 μg/L in plasma and 75-200 μg/L in urine have been recommended. However, there is no clearly defined, presumably normal cobalt supplementation regimen for horses and characterisation of potential adverse effects of any established threshold cobalt concentrations has not been done. This review outlines the strengths and limitations of the existing literature on the pharmacological effects of cobalt in horses with some recommendations on what gaps to bridge to enable the determination of optimal threshold cobalt concentrations in racing horses.
Keywords: Erythropoiesis; Hypoxia-inducible-factor; Pharmacodynamics; Pharmacokinetics; Toxicity.
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