Markers of bone turnover, parathyroid hormone, calcium, and magnesium concentrations in horses with acute colitis.
Authors: Kamr Ahmed, Fortin-Trahan Rosalie, Arroyo Luis G, Hostnik Laura D, Gomez Diego E, Toribio Ramiro E
Journal: Veterinary journal (London, England : 1997)
Summary
Acute colitis in horses frequently triggers hypocalcaemia, yet the underlying bone and mineral metabolism changes have received limited investigation. This study of 127 colitic and 36 healthy horses measured serum parathyroid hormone (PTH), calcium fractions (total and ionised), phosphorus, magnesium, and bone turnover markers—specifically C-terminal telopeptide of type I collagen (CTX-I, indicating resorption) and osteocalcin (OCN, indicating formation)—to determine whether bone mobilisation adequately compensates for calcium loss and whether these markers predict mortality. Colitic horses exhibited markedly elevated CTX-I and PTH alongside significantly depressed ionised calcium, total calcium, phosphorus, magnesium, and OCN concentrations compared with healthy controls; notably, horses presenting with ionised calcium below 1.4 mmol/L or PTH exceeding 92.9 pg/mL demonstrated substantially increased mortality risk (odds ratios of 6.1 and 3.6 respectively). The findings suggest that whilst bone resorption is upregulated in response to hypocalcaemia, this adaptive response proves insufficient in non-surviving horses, possibly due to PTH resistance, resulting in persistent hypocalcaemia that carries poor prognostic significance. For practitioners managing acute colitis cases, serial monitoring of ionised calcium and PTH concentrations may help identify high-risk individuals requiring intensified supportive care, and the pattern of elevated bone resorption with suppressed bone formation warrants investigation into whether targeted calcium and magnesium supplementation protocols could improve outcomes.
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Practical Takeaways
- •Monitor serum ionized calcium and PTH concentrations in horses with acute colitis as these are strong predictors of mortality risk
- •Elevated PTH with persistent hypocalcemia in colitic horses suggests PTH resistance may be contributing to poor outcomes and warrants aggressive clinical intervention
- •Decreased serum magnesium and phosphorus in colitic horses may impair the calcium-regulating mechanisms, so supplementation strategies should be considered alongside standard colitis treatment
Key Findings
- •Horses with acute colitis had significantly elevated serum CTX-I and PTH concentrations but lower osteocalcin, total calcium, ionized calcium, phosphorus, and magnesium compared to healthy horses
- •In colitis horses with ionized hypocalcemia, serum CTX-I concentrations were positively correlated with PTH concentrations
- •Colitis horses with ionized calcium <1.4 mmol/L had 6.1-fold increased odds of mortality, and those with PTH >92.9 pg/mL had 3.6-fold increased odds of mortality
- •Elevated PTH and CTX-I with decreased osteocalcin suggests increased bone turnover to offset hypocalcemia, but bone resorption activity was insufficient in non-surviving horses, indicating possible PTH resistance