Review maps strengths and limits of noninvasive cortisol testing in pigs
Bottom line
Version 1
A new narrative review in Animals pulls together the evidence on using saliva, urine, feces, and hair, rather than blood, to measure cortisol in intensively housed pigs. The authors argue these non- or minimally invasive samples can reduce the confounding effect of handling and restraint that comes with blood collection, but they also show that each matrix reflects a different biological time window and comes with its own collection, validation, and interpretation limits. In short, saliva is best for rapid changes, urine and feces capture a longer integrated signal, and hair may reflect longer-term exposure, though contamination remains a major concern. (mdpi.com)
Why it matters: For veterinary professionals working in swine health and welfare, the review is a useful reminder that “cortisol” isn’t a single interchangeable measure. Sampling method can shape the result as much as the biology does. That matters for welfare audits, research design, herd investigations, and interpretation of stress around procedures, transport, regrouping, heat, or housing changes. The broader pig welfare literature has increasingly emphasized less invasive biomarkers, but it also warns that pre-analytical variables, dilution effects in urine, lag times in feces, and environmental contamination of hair can all distort conclusions if protocols aren’t standardized. (pmc.ncbi.nlm.nih.gov)
What to watch: Expect more work on standardized sampling protocols, assay validation, and combining cortisol data with other welfare indicators rather than relying on a single biomarker alone. (pmc.ncbi.nlm.nih.gov)
Version 2
A new review in Animals examines whether saliva, urine, feces, and hair can offer more practical and welfare-friendly ways to measure adrenocortical activity in intensively housed pigs. The central issue is familiar to swine veterinarians and welfare researchers: blood cortisol is widely used, but the act of restraint and sampling can itself raise cortisol, making it harder to separate the animal’s baseline stress physiology from the stress of the test. The review positions alternative matrices as a way to reduce that problem, while also warning that none of them is plug-and-play. (mdpi.com)
That framing fits with a broader shift in pig welfare science. Over the past several years, reviews and field studies have pushed toward less invasive biomarkers that can be collected repeatedly with less disruption to the animal. Saliva has drawn particular interest because it can reflect relatively rapid hypothalamic-pituitary-adrenal axis responses, while urine and feces provide a more integrated picture over hours, and hair has been studied as a potential longer-term marker. At the same time, regulators and scientific bodies in Europe have continued to press for stronger animal-based welfare assessment in pigs, reinforcing the need for measures that are both biologically meaningful and feasible on farm. (pmc.ncbi.nlm.nih.gov)
According to the review, the value of each matrix depends heavily on the question being asked. Saliva is useful for acute responses, but collection conditions matter and the sampling event itself can still influence results if pigs are disturbed. Urine integrates cortisol secretion over the period of bladder filling, but interpretation requires attention to dilution correction. Fecal measures offer a delayed, cumulative signal that may be useful for monitoring stress over time, though timing and gut passage complicate attribution to a specific event. Hair appears attractive for longer-term assessment, but it is especially vulnerable to confounding from external contamination in intensive housing environments where pigs are in frequent contact with urine, feces, and saliva. (mdpi.com)
That last point is one of the most important cautions for practice. A 2020 study cited in the wider literature found that contamination with urine caused a considerable, concentration-dependent increase in hair cortisol concentrations in pigs, and concluded that contamination-derived cortisol could not be reliably distinguished from cortisol incorporated from blood. A later swine hair study also showed that wash protocol and contamination level can materially affect measured concentrations. Together, those findings support the review’s message that hair cortisol may be informative, but only with careful protocol design and conservative interpretation. (pubmed.ncbi.nlm.nih.gov)
Direct outside commentary on this specific review was limited in the material available through search, but the surrounding literature points in the same direction. Recent reviews on pig stress biomarkers and saliva-based diagnostics describe noninvasive sampling as promising for repeated welfare monitoring, while also stressing the need for analytical validation, matrix-specific reference frameworks, and attention to confounders such as disease, circadian effects, and handling. In other words, the industry reaction appears less like skepticism about noninvasive cortisol testing itself, and more like a push for better standardization before these tools are overinterpreted. (pmc.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, this review is most useful as a decision-making framework. If the goal is to evaluate an acute handling event, saliva may be the best fit. If the question is cumulative stress over a longer interval, urine, feces, or possibly hair may be more appropriate, but only if the team understands the biological lag and sample-specific pitfalls. That matters for herd welfare investigations, protocol validation, research studies, and conversations with producers about what a cortisol result can, and cannot, mean. A single cortisol number without context can mislead; a matrix chosen to match the clinical or welfare question is far more defensible. (mdpi.com)
The review also lands at a time when pig welfare assessment is becoming more multidimensional. Scientific and regulatory discussions increasingly connect welfare with housing, management, transport, health, and public health outcomes, which makes it less likely that one biomarker will ever stand alone. For veterinarians, the practical implication is that cortisol works best as part of a panel of evidence, alongside behavior, lesions, production data, environmental measures, and other physiological markers, rather than as a solitary verdict on welfare. (efsa.europa.eu)
What to watch: The next step is likely more validation in commercial settings, especially around standardized collection protocols, contamination control, and interpretation thresholds for different ages, production stages, and housing systems. Expect future work to focus on combining noninvasive cortisol measures with other biomarkers and automated welfare monitoring tools, which could make these tests more useful in real-world herd surveillance rather than only in controlled studies. (pubmed.ncbi.nlm.nih.gov)