Markers of bone turnover, parathyroid hormone, calcium, and magnesium concentrations in horses with acute colitis.

Overview

• This study investigated the relationship between bone turnover markers, parathyroid hormone (PTH), calcium, magnesium levels, and survival in horses suffering from acute colitis, a condition associated with low blood calcium (hypocalcemia).

Background and Purpose of the Study

• Hypocalcemia (low calcium levels in the blood) commonly occurs in horses with acute colitis, an inflammatory condition of the colon.
• Previous information on how serum PTH levels and bone turnover markers relate to this hypocalcemia in horses with colitis was insufficient.
• The goal was to analyze how bone resorption and formation markers correlate with PTH, calcium (total and ionized), phosphorus, magnesium levels, and mortality risk in horses with acute colitis.

Study Design and Methods

• A total of 163 horses were enrolled: 127 diagnosed with acute colitis and 36 healthy controls.
• Blood samples were collected from all horses for measurement of:
  • Bone resorption marker: C-terminal telopeptide of type I collagen (CTX-I)
  • Bone formation marker: Osteocalcin (OCN)
  • Serum parathyroid hormone (PTH)
  • Total calcium (tCa) and ionized calcium (iCa)
  • Phosphorus (Pi)
  • Total magnesium (tMg)
• Statistical analysis used non-parametric methods to compare values between colitis and healthy groups and to evaluate correlations and mortality associations.

Key Findings

• Compared to healthy horses, those with colitis had:
  • Higher serum CTX-I (bone resorption) and PTH levels.
  • Lower serum OCN (bone formation), total calcium, ionized calcium, phosphorus, and magnesium levels.
• In horses with colitis and ionized hypocalcemia, serum CTX-I positively correlated with PTH, suggesting increased bone resorption in response to hypocalcemia.
• Horses with very high PTH (>92.9 pg/mL) or very low ionized calcium were significantly more likely to die, indicating these as poor prognostic markers.

Interpretation and Implications

• Elevated PTH and CTX-I along with decreased OCN in colitis horses suggest increased bone turnover activity aimed at offsetting low blood calcium.
• Despite this, some horses did not survive, indicating their bone resorption response was insufficient to restore normal calcium levels.
• Possible development of PTH resistance (the body’s diminished response to PTH) may have contributed to persistent hypocalcemia in non-surviving horses.
• These findings highlight the complex hormonal and metabolic disturbances in equine colitis and suggest that monitoring bone turnover markers and calcium/PTH levels could help predict outcomes.

Conclusions

• The study provides evidence that acute colitis in horses induces significant disturbances in mineral metabolism and bone turnover, with elevated PTH-driven bone resorption attempting to counteract hypocalcemia.
• Failure to correct calcium imbalance, possibly due to PTH resistance, is linked with higher mortality, underscoring the need for therapeutic strategies targeting mineral metabolism in colitis management.