Effect of sample storage on pH-value in equine faeces

Lay Summary Measuring the pH-value in equine faeces is commonly performed in studies on equine nutrition and health. It is known that sample handling can have an undesired impact on the accuracy of such pH-measurements, but despite this, a common standard protocol for measuring pH in equine faeces is lacking. In this study, effects of storage time and temperature prior to measurement of pH in equine faecal samples was investigated. Faecal samples were collected from 105 horses. Each sample was divided into subsamples that were stored in room temperature, in a refrigerator and in a freezer for different time periods before measuring the pH-value. These measurements were compared with the pH-value measured directly at sampling, which was regarded as the reference. The comparisons showed that faecal samples stored in a refrigerator for 2-4 h had lower pH-values, and samples stored for 12-24 h had higher pH-values, compared to the reference. All samples stored in a freezer had higher pH-values than the reference. Samples stored in room temperature for 2 h or in a refrigerator for 8 h or 48 h had pH-values similar to the reference, and these storage options are therefore recommended if pH cannot me measured directly at sampling.