Review finds promise, but limits, for equine behavior biomarkers: full analysis

A new scoping review in BMC Veterinary Research argues that neuroendocrinological biomarkers remain promising, but not yet practice-ready, for equine behavioral medicine. Published on April 27, 2026, the review by Tiago Mendonça, Gesiane Ribeiro, Tomás Casqueiro, colleagues, and Daniel S. Mills surveyed the literature from the past two decades and identified ACTH, cortisol, and serotonin as the most frequently studied candidates, with oxytocin, melatonin, dopamine, and tryptophan discussed less often. The authors’ central message is cautious: the field is active, but methodological inconsistency still limits clinical interpretation. (link.springer.com)

That conclusion lands in a field where pressure for more objective welfare and behavior measures has been building for years. Equine clinicians, trainers, and pet parents increasingly want tools that can move assessment beyond observation alone, especially in cases involving chronic stress, pain-linked behavior change, stereotypies, or questions about welfare under training and management conditions. Earlier reviews have made a similar point from another angle: biomarkers are attractive because behavior can be context-dependent and subjective, but endocrine markers are also difficult to interpret in isolation. (link.springer.com)

According to the review, the problem isn’t a lack of candidate markers so much as a lack of comparability. The authors highlight differences in sampling protocols, assay methods, units of measurement, subject characteristics, and environmental context as major barriers to establishing useful reference values. Their conclusion is that this heterogeneity likely explains why so many studies end with the same recommendation for more research. They also argue that clinically useful biomarker work will require both agreed definitions of the subjective states being measured and more standardized collection and reporting protocols. (link.springer.com)

That caution is consistent with the broader equine welfare literature. A widely cited review on horse welfare found that cortisol results are often contradictory and may reflect temporary arousal rather than welfare status on their own, while serotonin and oxytocin have shown potential links to positive or negative affect but with mixed findings. Individual studies have associated circulating oxytocin and serotonin with traits such as docility and friendliness, while other work has found no clear change in oxytocin around putatively positive interactions like grooming. In other words, the signal may be real, but it is noisy, context-sensitive, and unlikely to be captured by a single analyte. (pmc.ncbi.nlm.nih.gov)

There’s also a wider industry backdrop here. New equine biomarker studies continue to appear across welfare, training, exercise, and clinical medicine, including recent work in BMC Veterinary Research examining cortisol, oxytocin, serotonin, and brain-derived neurotrophic factor across training regimens. Outside behavior specifically, equine clinicians are already comfortable with biomarkers in other domains, such as inflammatory markers, which may help explain why interest in behavioral biomarkers is accelerating. The difference is that behavioral medicine demands stronger standardization because emotional valence, arousal, pain, handling, and sampling stress can all influence the same pathways. (link.springer.com)

Why it matters: For veterinary professionals, this review supports a measured approach. It strengthens the case for following biomarker research in equine behavior medicine, but it does not support routine use of cortisol, ACTH, serotonin, or oxytocin as standalone diagnostic tools for behavioral cases today. In practice, the most defensible near-term use may be as part of multimodal assessment, paired with history, physical examination, pain workup, management review, and structured behavioral observation. For clinicians advising pet parents, that’s an important distinction: a lab value may eventually add clarity, but today it can just as easily overpromise objectivity if the context behind the number isn’t well controlled. (link.springer.com)

The review may also help frame future research priorities. The authors say their synthesis provides a basis for developing assays for more routine use, but only if the field can agree on what states are being measured and how samples should be collected and reported. That likely means more prospective studies in real-world clinical environments, more work on multi-biomarker panels rather than single markers, and tighter integration of physiology with validated behavioral endpoints. (link.springer.com)

What to watch: The next meaningful milestone won’t be another list of candidate biomarkers, but validation studies showing that standardized panels can reliably distinguish stress, pain, positive affect, or chronic welfare compromise in horses seen under everyday veterinary conditions. (link.springer.com)