Calcium homeostasis and intact plasma parathyroid hormone during exercise and training in young Standardbred horses.
Authors: Vervuert I, Coenen M, Wedemeyer U, Chrobok C, Harmeyer J, Sporleder H-P
Journal: Equine veterinary journal
Summary
# Editorial Summary Young Standardbred horses undergoing an intensive six-week training programme showed exercise-induced changes in calcium regulation that varied markedly depending on exercise intensity. Seven untrained horses completed a lactate-guided training protocol alternating between high-speed efforts (15 minutes at progressively increasing velocities from VLa4) and prolonged low-speed work (60–90 minutes at VLa2.5), with blood sampling before, during and after exercise bouts and standardised incremental tests at the beginning and end of training. High-intensity exercise triggered a significant drop in ionised calcium and blood pH alongside elevated lactate, phosphorus and intact parathyroid hormone (PTH), whereas low-intensity exercise increased pH without affecting calcium or PTH; these hormonal responses remained consistent between the first and eighth repetitions of each exercise type, suggesting no adaptive dampening over the training period. The findings indicate that PTH acts as a homeostatic counter-regulator during intense anaerobic work, offsetting exercise-induced hypocalcaemia through calcium mobilisation—a response triggered by the metabolic acidosis accompanying high-speed efforts rather than by training duration itself. For practitioners managing young performance horses, this suggests that intense interval work may create acute demands on calcium regulation through hormonal mechanisms, potentially relevant when considering mineral supplementation strategies or monitoring metabolic stress during conditioning programmes.
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Practical Takeaways
- •High-intensity exercise triggers acute changes in calcium metabolism and PTH response; understanding this normal physiological response can help differentiate exercise effects from pathology
- •Low-intensity, sustained exercise does not disrupt calcium homeostasis despite equal energy expenditure, suggesting training intensity rather than total work load drives metabolic changes
- •The PTH system effectively regulates exercise-induced hypocalcaemia without requiring intervention, suggesting horses naturally adapt to repeated exercise stress over a training programme
Key Findings
- •High-speed exercise and incremental exercise tests caused decreased ionised calcium and pH with increased lactate and intact PTH
- •Low-speed exercise at constant velocity did not affect lactate, ionised calcium, total calcium, phosphorus or PTH despite similar energy expenditure
- •Intact PTH appears to mediate counter-regulation of exercise-induced hypocalcaemia in horses
- •No changes in calcium metabolism were detected across the 6-week training programme despite repeated exercise sessions