Distilled Water Dilution Increases Measured Fecal pH in Fresh Canine Feces

Fecal pH is used in canine nutrition studies as an indirect indicator of intestinal fermentation, but sample preparation may affect the measured value. This study evaluated the effect of different feces-to-water dilution ratios on pH determination in canine feces. Thirty-seven samples from 20 healthy dogs were evaluated using five preparation protocols: direct measurement without dilution and dilution with distilled water at 1:1, 1:2, 1:5, and 1:10 feces-to-water ratios, on a weight-to-volume basis. Sample preparation affected fecal pH (p < 0.0001). The least-squares mean pH was 6.37 for direct measurement, 6.54 for 1:1, 6.71 for 1:2, 6.88 for 1:5, and 7.04 for 1:10. Fecal pH increased progressively with increasing water addition, with significant differences among all preparation protocols. Regression analysis confirmed that water addition increased measured fecal pH, and the response was better described by a quadratic model than by a linear model. These findings show that the amount of water added is a relevant methodological factor in fecal pH determination. Among the protocols evaluated, the 1:1 feces-to-water ratio appears to be the most suitable standardized method for routine analysis because it used the lowest amount of water while providing adequate conditions for homogenization and electrode contact.