Measuring Back Pain in Horses

Hello Summarians!

How to measure pain and dysfunction? This is a great question. Previously, we had to rely on the experienced eye of highly trained specialists, and we still do, but now we have other tools to assist in making a diagnosis.

High-speed videography enabled the estimation of movement details but could only be viewed in one dimension. Our first study looks to step up the amount and type of data that can be gathered and analyzed.

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New Way To Measure Back Pain In Horses

This paper reframes the long-standing and poorly defined concept of equine “back pain” as topline dysfunction, a multifactorial syndrome characterized by pain, stiffness, and reduced mobility of the spine that manifests as poor performance, behavioral issues, and sometimes lameness. Despite decades of clinical recognition, diagnosis and monitoring remain challenging because current assessments rely heavily on subjective palpation, mobilization tests, and clinician judgment, all of which show poor interobserver reliability. Although objective tools exist for lameness detection and pain sensitivity, there has been no validated system to objectively assess the spinal quality of movement in horses. 

To address this gap, the study introduces a noninvasive, three-dimensional motion analysis approach using cluster-based reflective markers and the calibrated anatomical system technique (CAST). Unlike traditional single-marker methods that primarily capture sagittal plane motion, this approach allows six-degrees-of-freedom tracking and quantification of intersegmental spinal angles and angular velocities across multiple spinal regions. The authors applied this method to compare spinal motion in sound horses and a clinically lame horse during walking and trotting. 

The findings show that intersegmental spinal motion patterns measured with this noninvasive method are consistent with prior invasive bone-pin studies, supporting its biomechanical validity. In sound horses, lateral bending predominated in the thoracic spine, while flexion–extension was greatest at the lumbosacral junction, aligning with established literature. Importantly, differences between sound and lame horses were more clearly and sensitively detected using angular velocity rather than joint angles alone. While angle data primarily identified changes in the sagittal plane, angular velocity revealed marked differences across all three planes, even at the walk when the lame horse appeared visually sound. 

These elevated angular velocities in the lame horse likely reflect altered postural control and reduced quality of movement, paralleling findings in humans with chronic low back pain. The results suggest that angular velocity may be a particularly sensitive marker of impaired spinal control and could serve as a valuable objective outcome measure for diagnosing topline dysfunction and monitoring response to treatment. 

Although limited by a small sample size and the inclusion of only one lame horse, the study demonstrates the feasibility and clinical promise of this approach. Overall, it provides the first evidence that noninvasive cluster-based motion capture combined with angular velocity analysis can objectively characterize equine spinal function in all three planes, offering a meaningful advance toward standardized, quantitative assessment of topline dysfunction in horses. 

Ursini, T. L., Clayton, H. M., Levine, D., & Richards, J. (2026). Multiplanar intersegmental angular velocity in the assessment of topline movement in horses. American Journal of Veterinary Research https://doi.org/10.2460/ajvr.25.09.0331 

Bottom line — Exciting development, but more study is needed.

Ondansetron Kintetics In Dogs

Ondansetron is commonly used in veterinary medicine to manage nausea and vomiting, particularly because alternative anti-nausea options are limited. While maropitant is a potent antiemetic, its anti-nausea effects appear inferior to injectable ondansetron, and metoclopramide has inconsistent anti-nausea efficacy and an impractically short half-life in dogs. As a result, ondansetron—especially in oral form—is frequently prescribed despite limited pharmacokinetic data supporting its effectiveness in veterinary patients. 

This study compared the pharmacokinetics of intravenous and oral ondansetron in healthy client-owned dogs using a crossover design. Consistent with previous work, oral ondansetron demonstrated extremely low bioavailability at a dose of 1 mg/kg, likely due to extensive first-pass metabolism. In contrast, intravenous administration reliably achieved plasma concentrations within the presumed therapeutic range. These findings raise concerns about the clinical efficacy of oral ondansetron in healthy dogs, even though anecdotal reports and limited studies suggest it may still provide some anti-nausea benefit. 

One possible explanation for these observations is that oral ondansetron may exert local effects in the gastrointestinal tract that are not reflected by plasma concentrations, given the abundance of 5-HT3 receptors in the gut. Additionally, pharmacokinetics may differ in dogs with hepatic or renal disease, where reduced clearance could lead to higher systemic exposure, potentially improving efficacy in these commonly nauseous populations. Study limitations included a small sample size, limited sampling duration, and use of only healthy dogs. Overall, the findings indicate that oral ondansetron has very low bioavailability in healthy dogs, and future studies should focus on correlating plasma concentrations with clinical nausea outcomes, particularly in diseased patient populations where oral therapy may be more effective. 

Garrick, A., Zersen, K., Gustafson, D., Quimby, J., Diaz, A., and Shropshire, S. (2026), Bioavailability of Oral Ondansetron in Dogs: A Crossover Study. J Vet Pharmacol Therap, 49: 17-21. https://doi.org/10.1111/jvp.70024 

Bottom line — Poorly absorbed orally.

CBD Versus CBDA In Horses

This study places cannabidiol (CBD) and cannabidiolic acid (CBDA) within the broader context of cannabinoid research and veterinary medicine, emphasizing the need to understand their pharmacokinetics and safety before clinical use in horses. While CBD has been widely studied in dogs, cats, and increasingly in horses, oral bioavailability in horses is consistently low, which may limit its ability to reach therapeutic plasma concentrations. In contrast, CBDA—a structurally related precursor that readily decarboxylates to CBD—has shown promising anti-inflammatory, anti-nociceptive, and anti-convulsant effects in preclinical models and emerging veterinary studies, largely without psychotropic effects. 

The primary aim of the study was to directly compare plasma and urine exposure of CBD and CBDA in horses after a single oral dose of equivalent molar amounts, using formulations containing only one cannabinoid. The results demonstrated a striking difference in systemic exposure. Despite similar molar dosing, CBDA produced plasma concentrations and total exposure (AUC) that were approximately 14–36 times higher than those of CBD, with peak concentrations 25–67 times greater. This disparity cannot be explained by small differences in molecular weight or dose, suggesting that CBDA is absorbed more efficiently, undergoes less first-pass metabolism, or is cleared more slowly than CBD. Urinary concentrations showed a similar trend, though with greater variability. 

The pharmacokinetic profile of CBD observed here aligns with previous equine studies, including rapid absorption, a relatively short terminal half-life, and low oral bioavailability. Differences between studies in reported half-lives and compartmental models likely reflect methodological factors such as sampling duration, assay sensitivity, dosing level, and whether intravenous administration was included. Evidence from repeated-dose studies indicates that CBD can accumulate in peripheral tissues, potentially explaining reported clinical effects at relatively low daily doses. Importantly, available data—including this study—suggest that short-term oral CBD administration at low to moderate doses is generally well tolerated in horses, with minimal adverse effects. 

The markedly higher exposure of CBDA increases the likelihood of achieving pharmacologically active concentrations and may translate into greater clinical efficacy, particularly if CBDA is indeed more potent than CBD, as suggested by rodent models. However, CBDA’s chemical instability remains a limitation. Emerging work on more stable analogs, such as CBDA-methyl ester, which has shown efficacy in pain and nausea models, points toward future directions. Overall, the findings strongly support further pharmacokinetic, pharmacodynamic, and clinical studies of CBDA and its analogs in horses, as a necessary step toward evidence-based cannabinoid therapeutics in equine medicine. 

Ekstrand, C., Michanek, P., Hernlund, E., Gehring, R., Spjut, K., and Salomonsson, M. (2026), Differences in Plasma Exposure of Cannabidiol and Cannabidiolic Acid Following Oral Administration to Horses. J Vet Pharmacol Therap, 49: 22-32. https://doi.org/10.1111/jvp.70027

Bottom line — CBDA might be a better fit kinetically.

Just putting things in perspective …