Comparison of volumetric urine collection versus single-sample urine collection in horses consuming diets varying in cation-anion balance.

The research article investigates the differences between volumetric urine collection and single-sample urine collection in horses, and how these different methods of urine collection might influence the measurement of electrolyte and mineral excretion when the horses are being fed diets varied by their dietary cation-anion balance (DCAB).

Objective and Methodology

The researchers designed a study to:

• Observe daily variation in clearance and fractional excretion (FE) of electrolytes and minerals in horses both within individual horses and between different horses.
• Compare the operations and outcomes of volumetric and single-sample urine collection methods for determining FE values of diets across a range of DCAB levels.

They conducted their tests on 11 mares (5 Thoroughbred and 6 mixed-breed) and subjected them to different diets—low, medium, and high DCAB diets—at 14-day intervals. Over the last 72 hours in each dietary phase, they collected daily blood samples and both volumetric and single-sample urine collections.

Findings

The research findings include:

• Clear alterations noticed in urine and plasma pH values, plasma concentrations, and FE values of electrolytes (sodium, chloride, potassium) and minerals (magnesium, phosphorus, and calcium) resulting from the adjustments in DCAB.
• Clear and noticeable day-to-day variation in clearance and FE values was detected within individual horses on the same diet as well as between horses.
• The FE values, overall, were not significantly different whether measured by volumetric methods or single-sample methods except for magnesium in the high DCAB diet.
• Both volumetric and single-sample collections offered similar patterns of change in urinary FE values with varying DCAB, but exceptions were found with calcium and magnesium.

Conclusion

The findings led the researchers to conclude that:

• There is substantial variation in clearance and FE of electrolytes and minerals within horses across 24-hour periods as well as between horses fed a specific diet.
• Daily collection of three urine samples provides largely similar information on dietary-induced changes in clearance and FE values, comparable to that obtained by volumetric urine collection. However, this alleged similarity doesn’t pertain to calcium and magnesium values.

This suggests that for most electrolytes and minerals, single-sample urine collection may be as effective as volumetric collection. However, when specifically considering magnesium (and to a lesser extent, calcium), the volumetric method provides more accurate FE values.