Study finds dilution raises measured fecal pH in dogs
Bottom line
A new study in Animals found that adding distilled water to fresh canine feces before pH testing raises the measured pH, and that the effect grows as the dilution increases. Researchers Pedro Henrique Marchi, Carolina Dantas Micheletti, and Jennifer Machado de Souza evaluated 37 samples from 20 healthy dogs using five preparation methods: direct measurement and feces-to-water dilutions of 1:1, 1:2, 1:5, and 1:10. Their conclusion is straightforward: sample preparation changes the result, so fecal pH values from different studies may not be directly comparable if the dilution protocol differs. That matters because fecal pH is widely used in canine nutrition research as a proxy for hindgut fermentation, yet published dog studies use a range of dilution methods, including 1:1, 1:5, and 1:10 water-based preparations. (pmc.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, especially those involved in nutrition research, GI studies, or product development, the paper is a reminder that pre-analytic handling can shape the biomarker as much as biology does. If dilution with distilled water systematically shifts pH upward, then changes attributed to diet, microbiome modulation, or fermentation may partly reflect method differences instead. The practical takeaway is less about changing clinical care tomorrow and more about tightening protocols, reporting methods clearly, and being cautious when comparing fecal pH across trials, diets, or laboratories. Broader canine stool research has already highlighted the value of standardized sampling and homogenization to reduce variability. (pmc.ncbi.nlm.nih.gov)
What to watch: Watch for follow-up work on standardizing canine fecal pH methods, including whether journals and nutrition researchers begin favoring one dilution ratio, or direct measurement, for cross-study consistency. (pmc.ncbi.nlm.nih.gov)
Key facts
- Study
- Published in Animals
- Finding
- Adding distilled water to fresh canine feces before pH testing increased the measured pH
- Dose-response
- Higher dilution ratios produced higher pH readings
- Samples
- 37 samples from 20 healthy dogs
- Methods
- Direct measurement, plus 1:1, 1:2, 1:5, and 1:10 distilled-water dilutions
- Interpretation
- Fecal pH values from different studies may not be directly comparable if dilution protocols differ
- Use in research
- Fecal pH is widely used in canine nutrition research as a proxy for hindgut fermentation
A study published in Animals is putting a methodological detail under the microscope: how much distilled water is added before measuring fecal pH in dogs. The researchers report that dilution increases the measured pH of fresh canine feces, with higher water ratios producing higher readings. In a field where fecal pH is often used as an indirect marker of intestinal fermentation, that finding suggests some published differences may reflect lab technique, not just biology. (mdpi.com)
The issue matters because canine nutrition and GI studies have never fully settled on one preparation method. Published protocols vary widely. Some studies measure pH after 1:1 dilution, others use 1:5 or 1:10, and still others emphasize rapid handling, homogenization, or frozen-thawed samples. That variability has persisted even as fecal pH has become a routine endpoint in work on protein levels, fiber, prebiotics, probiotics, postbiotics, and broader gut health. (pmc.ncbi.nlm.nih.gov)
According to the study abstract, the team analyzed 37 samples from 20 healthy dogs using five protocols: no dilution, plus distilled-water dilutions of 1:1, 1:2, 1:5, and 1:10 on a weight-to-volume basis. The central result was that distilled water dilution increased measured fecal pH, and the increase tracked with the degree of dilution. Based on that design, the authors are effectively arguing that the preparation step is not neutral, and that dilution itself can move the number investigators are trying to interpret. (mdpi.com)
That conclusion fits with the broader literature, where fecal pH is often treated as a downstream signal of microbial fermentation, especially short-chain fatty acid production. Reference texts note that short-chain fatty acids lower large-intestinal pH, and many canine feeding trials use fecal pH alongside ammonia, SCFAs, and stool quality as a gut-health package of endpoints. But if the measured pH changes with added water, then the signal can be partly methodological. In practical terms, a 1:10 dilution protocol may not be reading the same thing as a direct probe in fresh stool, even when both are labeled simply as “fecal pH.” (merckvetmanual.com)
I didn’t find substantial outside expert commentary tied specifically to this paper, but related methodological work points in the same direction. A canine stool variability study concluded that standardization and complete homogenization can improve consistency in stool-based analyses, while an equine paper explicitly proposed a standard fecal pH protocol to reduce variation across studies. Taken together, that suggests the new dog study is landing in an area where researchers already recognize that sample handling can distort interpretation. (pmc.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, this is mainly a research-quality and interpretation story. Clinicians are unlikely to change routine patient care based on fecal pH dilution alone, because fecal pH is used more often in research than in day-to-day practice. But for veterinary nutrition teams, academic investigators, diagnostic labs, and companies running feeding trials, the paper is a caution against comparing pH values across studies without checking the method section first. A diet that appears to “raise” or “lower” fecal pH in one paper may not be directly comparable with another if one used direct measurement and the other used a 1:10 distilled-water dilution. (mdpi.com)
There’s also a reporting issue here. Many published canine studies do state their dilution ratio, but those details can be easy to overlook when pH is summarized as a secondary endpoint. If this paper gains traction, it could push authors, reviewers, and editors to ask for tighter method reporting and, eventually, harmonized protocols. That would make it easier to compare diets, supplements, and microbiome-targeted interventions across institutions and over time. (pmc.ncbi.nlm.nih.gov)
What to watch: The next step is whether this remains a useful cautionary note or becomes a standardization push. Watch for future canine nutrition and GI studies to justify their fecal pH method more explicitly, compare direct and diluted measurements prospectively, or pair pH with better-standardized fermentation markers such as SCFAs adjusted for fecal dry matter. If that happens, this paper may end up having more influence on study design than on any single biological conclusion. (frontiersin.org)