Validation of diagnostic tests for determination of magnesium status in horses with reduced magnesium intake

Plasma-Ionized Magnesium in Hospitalized Horses with Gastrointestinal Disorders and Systemic Inflammatory Response Syndrome

Simple Summary

Gastrointestinal diseases are the most prevalent diseases in hospitalized horses. One of the predisposing factors of decreased intestinal motility in horses with colic could be low plasma calcium concentration and related magnesium imbalances. Magnesium and calcium disturbances can predispose to decreased intestinal motility in horses with colic after abdominal surgery. Plasma ionized magnesium concentrations were measured in hospitalized horses with different types of gastrointestinal disorders (i.e., colic), horses with non-gastrointestinal diseases, horses with systemic inflammatory conditions and control horses; our results allowed us to conclude that hypomagnesemia was more prevalent in horses with obstructive gastrointestinal lesions. Surprisingly, no association was found with systemic inflammatory conditions nor with mortality. These valuable results suggest to us that magnesium concentrations in horses presenting obstructive colic should be monitored. Further research is needed to evaluate the effects of intravenous magnesium supplementation in horses with gastrointestinal diseases.

Abstract

Magnesium disorders in horses with gastrointestinal disorders or systemic inflammatory response syndrome (SIRS) are scarcely characterized. The purpose of the study was to explore the association of magnesium disorders with diagnosis, SIRS and mortality in horses admitted to a referral equine hospital. In total, 75 sick horses were included in an observational prospective study and classified as: obstructive (n = 17), inflammatory (n = 10) and ischemic gastrointestinal disorders (n = 12), and other non-gastrointestinal systemic disorders (n = 36). All sick horses were also divided according to the presence (n = 26) or absence of SIRS, and survival to discharge from hospital (survivors (n = 61) and non-survivors (n = 14). In addition, 26 horses were included as controls. On admission, mean (iMg) (95% confidence interval (CI)) in the SIRS group (0.47 (0.43–0.50 mmol/L)) was within the normal range (0.4–0.6 mmol/L). The obstructive group had lower (iMg) compared to the control group (0.44 (0.38–0.51 mmol/L) vs. 0.56 (0.50–0.61 mmol/L); p = 0.001). In total, 8 out of 17 (47%) horses with obstructive lesions presented with hypomagnesemia compared to controls (4% (1/26)) (p = 0.001). In conclusion, hypomagnesemia was more prevalent on admission in horses in the obstructive group, and to a lesser extent, in the inflammatory and ischemic groups. In contrast to human ICU patients, the proportion of hospitalized horses with hypomagnesemia was not associated with mortality.

Magnesium disorders in horses

Magnesium (Mg) is an essential macroelement that is required for cellular energy-dependent reactions involving adenosine triphosphate and for the regulation of calcium channel function. Subclinical hypomagnesemia is common in critically ill humans and animals and increases the severity of the systemic inflammatory response syndrome; worsens the systemic response to endotoxins; and can lead to ileus, cardiac arrhythmias, refractory hypokalemia, and hypocalcemia. This article discusses the clinical signs, consequences, and treatment of hypomagnesemia in horses and describes the association of Mg and endotoxemia, insulin resistance, and brain injury.

Fractionation of calcium and magnesium in equine serum

OBJECTIVE

To establish reference values for protein-bound, ionized, and weak-acid complexed fractions of calcium and magnesium in equine serum and determine stability of ionized calcium (iCa) and ionized magnesium (iMg) in serum samples kept under various storage conditions.

ANIMALS

28 clinically normal horses.

PROCEDURE

Total calcium (tCa) and magnesium (tMg) in equine serum were fractionated by use of a micropartition system that allows separation of protein-bound calcium (pCa) and magnesium (pMg) and ultrafiltrable calcium (microCa) and magnesium (microMg) fractions. Serum concentrations of iCa and iMg were measured in the ultrafiltrate by use of selective electrodes. Serum concentration of complexed calcium (cCa) or magnesium (cMg) was calculated by subtracting iCa or iMg from microCa or microMg, respectively.

RESULTS

Mean +/-SE serum tCa concentration was 3.26 +/- 0.06 mmol/L. Calcium fractions were as follows: pCa, 1.55 +/- 0.03 mmol/L (47.4 +/- 0.9%); iCa, 1.58 +/- 0.03 mmol/L (48.5 +/- 0.7%); and cCa, 0.13 +/- 0.02 mmol/L (4.1 +/- 0.9%). Serum tMg concentration was 0.99 +/- 0.04 mmol/L. Magnesium fractions were as follows: pMg, 0.33 +/- 0.04 mmol/L (33.3 +/- 4.2%); iMg, 0.57 +/- 0.02 mmol/L (57.6 +/- 1.7%); and cMg, 0.09 +/- 0.02 mmol/L (9.1 +/- 1.9%). Refrigeration (4 degrees C) did not affect iCa values, whereas iMg declined by 8% after 120 hours. Neither iCa nor iMg was affected by freezing (-20 degrees C).

CONCLUSIONS AND CLINICAL RELEVANCE

In equine serum, iMg is less stable than iCa; thus, when serum samples are not going to be analyzed promptly, freezing may be preferable to refrigeration for storage.