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

The article evaluates the effectiveness of various diagnostic tests for identifying magnesium deficiency in horses. The researchers fed some horses a diet with reduced magnesium content, and contrasted their test results with a control group fed on a normal diet. The researchers found the 24-hour urinary magnesium excretion test to be the most sensitive indicator for detecting reduced magnesium intake.

Study Design and Methodology

• Nine young female horses were chosen for this research.
• Six out of these nine horses were given a magnesium-deficient diet for a span of 29 days and after that they were put on a magnesium-supplemented diet for a period of 24 days.
• The rest of the horses (three of them) were used as control samples and were only fed grass hay.
• The team of researchers collected blood, urine and tissue samples from the horses. They performed a magnesium retention test before and after restricting and supplementing the magnesium intake.

Measurements and Observations

• Various tests were performed on the collected samples, such as serum total magnesium (tMg), serum ionized magnesium (iMg), muscle magnesium, intracellular magnesium (icMg), and urine magnesium concentration measurements.
• The researchers made calculations on 24-hour urinary magnesium excretion (EMg), magnesium clearance (CMg), and fractional clearance of magnesium (FCMg).
• They found that reductions in urinary 24-hour EMg, CMg, and FCMg were evident after 13 days of feeding the horses a magnesium-reduced diet.
• However, serum tMg and iMg concentrations, muscle magnesium content, and results of the magnesium retention test were not affected by the magnesium-deficient diet.

Conclusions

• The researchers concluded that the 24-hour urinary magnesium excretion is the most sensitive and precise indicator of reduced magnesium intake in horses.
• Another findings was that the spot urine sample FCMg seemed to accurately reflect the FCMg calculated from 6- and 24-hour pooled urine samples. This provides a convenient way to identify horses that are consuming a diet deficient in magnesium.