Reliability of single-sample phosphorus fractional excretion determination as a measure of daily phosphorus renal clearance in equids

In 4 healthy horses and 1 Welsh pony, fractional renal excretions of phosphorus (FEp) determined from 9 hourly time collections taken over a 24-hour period were compared to assess whether a single-sample collection would be an accurate indicator of the daily FEp. The mean FEp for each animal varied from 0.115% to 0.302%; the 2 animals with the highest values were significantly different (P less than 0.05) from the 3 with the lowest values. Individual variation within animals was not great, however, because it was calculated that the 24-hour FEp value could be found within +/- 0.087% of the single sample value 95% of the time in a given animal.