Endurance horses that are retired from competition due to metabolic issues are often treated with intravenous fluids, with or without calcium supplementation. A collaborative California study by Loomis Basin Equine Medical Center, Foothill Equine and the University of California at Davis School of Veterinary Medicine examined the effects of supplemental calcium gluconate (0.4mg/kg/min) on heart rate, gastrointestinal sounds and serum electrolyte concentrations [Fielding, CL.; Deane, EL.; Major, DS. et al. Effects of calcium supplementation to resuscitation fluids in endurance horses: A randomized, blinded, clinical trial. J Vet Internal Med 2023, vol 37, pp 1216-122; DOI: 10.1111/jvim.16715].
The horses involved in the study were eliminated from the Tevis Cup 100-mile endurance ride and deemed sufficiently metabolically compromised to require intravenous fluids. Sixteen horses with mild to moderate clinical exhaustion were randomly selected to receive either a 23% calcium gluconate solution supplemented in 10 liters of isotonic fluids or given 10 liters of non-calcium containing isotonic fluids. All fluids were administered by gravity flow over an hour. Seven horses received calcium; nine horses served as controls. Blood and physical exam findings were reported before and after the hour-long treatment, and heart rates were recorded every 15 minutes during fluid administration. All horses recovered following treatment.
The results indicate that calcium supplementation in intravenous fluids more quickly reduced the horses’ heart rates than the non-calcium receiving controls. The horses did not experience bradycardia; just a more rapid return to resting heart rate through reduction of roughly 10 beats per minute. Two of the horses given calcium were retired from competition due to poor heart rate recovery and palpably taut muscles. Creatine kinase (CK) and aspartate aminotransferase (AST) also decreased in horses receiving calcium. The authors noted that calcium “did not appear to have detectable negative effects on horses with rhabdomyolysis.”
Of note is that the gastrointestinal sounds in the control group improved more than in the calcium-supplemented group. One thought is that calcium can affect vasoconstriction of splanchnic vessels with subsequently reduced gastrointestinal sounds.
The authors concluded: “Intravenous calcium supplementation to endurance horses eliminated from competition after development of metabolic problems may decrease heart rate but impairs improvement in gastrointestinal sounds.”