Cobalt is a rich dark blue-colored trace mineral naturally found in the Earth’s crust. Microbes in the equine hindgut use cobalt to make vitamin B-12 (cyanocobalamin) through the process of fermentation. Vitamin B-12, in turn, plays a role facilitating protein synthesis, and carbohydrate and fat metabolism. Cobalt, integrated into vitamin B-12, also promotes red blood cell formation.
Requirements and Dietary Sources
Cobalt is required in very small amounts in the equine diet. According to the National Research Council’s (NRC) Nutrient Requirements of Horses (2007), an average 1,100-pound (500-kilogram) horse only needs about ½ milligram of cobalt in his diet per day, although most horses typically consume a little more. (For reference, a sugar packet and a raisin each weigh about 1 gram, and 1 mg is 1/1000 of one gram!) Horses don’t typically doesn’t require cobalt supplementation.
Cobalt toxicity is unlikely to occur naturally in horses, although the true upper limit has not been established. The NRC’s maximum tolerable intake for horses is based on what’s known in other species, such as cattle, sheep, and swine, and is suggested to be approximately 25 milligrams per kilogram (11.4 milligrams per pound) of dry matter feed per day.
Cobalt is found in most horse feeds. Alfalfa and yeast are rich sources of cobalt, and cereal grains contain moderate amounts.
Cobalt deficiency would result in a vitamin B-12 deficiency, but no known deficiency has been reported in horses. In other species, excess cobalt is associated with negative effects on reproduction, cardiomyopathy, thyroid failure, and cancer (Kenobe 2016). Researchers are starting to learn that too much cobalt can be harmful to horses, as well.
In horses, cobalt supplementation has been scrutinized for its ability to promote red blood cell production (Ho et al. 2015), and has been used in human athletes for its performance-enhancing effects (Knych et al. 2015). Recent investigations have proven that cobalt has been abused in equine sports for this purpose. Horses’ baseline blood concentration of cobalt is around 1 part per billion (ppb), which is very low (Kynch et al. 2015). Studies showed that cobalt accumulates in body tissues over time, leveling off between nine and 33 days in horses (Kenobe 2016). Because cobalt has a long half-life of about 6 ½ days, testing can readily reveal abnormally high blood concentrations (Kynch et al. 2015). Investigation into the effects of repeated dosing of cobalt employed five Standardbred mares given fiveweekly intravenous doses of cobalt chloride (0.25, 0.5, 1, 2 or 4 mg/kg). Mares receiving 1, 2 or 4 mg/kg cobalt chloride showed signs of profound hypertension (high blood pressure) and tachycardia (high heart rate), and all mares showed signs of anxiety (Burns et al. 2016). While long term effects of excessive cobalt remain to be understood, it has been suggested that the risk of heart damage and sudden cardiac death are increased (Burns et al. 2016). Researchers suggested there was no therapeutic value for cobalt administration and that doses over 1 mg/kg had humane implications (Burns et al. 2016).
Cobalt is an essential trace mineral found naturally in most feedstuffs, and deficiency is rare. Supplementation is generally unnecessary, unless forages are grown in cobalt-deficient soils. Abuse of cobalt has negative physiologic effects, and researchers are actively working to understand long-term implications of cobalt excess.
Burns, T., Dembek, K., Dunbar, L., Brewington, S., Bednarski, L., O’Brien, C., Aarnes, T., Dooley, B., Lakritz, J. and Toribio, R. 2016. Proceedings of the 2016 American College of Veterinary Internal Medicint Forum. June 9-10, 2016.Denver, CO. p. 1498.
Coenen, M. 2013. Macro and trace elements in equine nutrition. In: Equine applied and clinical nutrition: Health, welfare and performance. Eds: Geor, R.J., Harris, P.A. and Coenen, M. Sauders Elsevier. pp. 190-228.
Ho, E.N.M., Chan, G.H.M., Wan, T.S.M., Curl, P., Riggs, C.M., Hurley, M.J., Sykes, D. 2015. Controlling the misuse of cobalt in horses. Drug Testing and Analysis. 7(1):21-30.
Kenobe, R.T. 2016. Towards elimination of excessive cobalt supplementation in racing horses: A pharmacological review. Research in Veterinary Science. 104:106-112.
Knych, H.K., Arthur, R.M., Mitchell, M.M., Holser, I., Poppenga, R., Smith, L.L., Helm, M.N., Sams, R.A. and Gaskill, C.L. 2015. Pharmacokinetics and selected pharmacodynamics of cobalt following a single intravenous administration to horses. Drug Testing and Analysis. 7(7):619-625.
Lewis, L.D. 1996. Minerals for horses. In: Feeding and care of the horse, 2nd edition. Lippincott Williams & Wilkins, Media, PA. pp. 19-41.
National Research Council. 2007. Nutrient Requiremtnes of Horses, 6th Edition. National Academies Press, Washington, DC.
Royal Society of Chemistry. Undated. Cobalt. Accessed online at: https://www.rsc.org/periodic-table/element/27/cobalt