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Pain Assessment of Horses With Trigeminal-Mediated Headshaking (TMHS) at Rest Between Episodes.
Abstract: While there is agreement that horses experience pain during the actual headshaking attacks, there is still a lack of research about the time between the individual episodes in this species. Objective: To evaluate the signs of pain in horses with TMHS at rest in the absence of common triggering factors. Methods: Twenty TMHS horses (not head shaking at the time of pain assessment), 20 horses with colic, and 20 clinically healthy horses. Methods: Descriptive study assessing pain in TMHS horses during the absence of clinical signs using the Horse Grimace scale (HGS). To grade the pain shown with TMHS, horses with moderate gastrointestinal pain conditions and a healthy horses' group were also included. For evaluation, videos were taken on two consecutive days from both sides of the face (healthy, TMHS) or before analgesics were applied (colic). Eight photos per horse were extracted from the videos, randomized, and evaluated by three examiner groups, each comprising two persons: (a) last-year veterinary medicine students without previous use of the HGS, (b) experienced veterinarians without experience in using the HGS, and (c) experienced veterinarians who regularly apply the HGS. All examiners were blinded to the underlying condition. Results: Median HGS scores in the groups (healthy, gastrointestinal, TMHS) differed significantly from each other (p < 0.05). Healthy horses had median HGS scores below 2 (median 1.2, range: 0.1-2.4), whereas TMHS horses had higher median HGS scores (5.6, range 2.4-7.4), and colic horses had the highest HGS scores (6.6, range: 3.8-8.4). There was a statistically significant difference for all facial action units (FAU) when the different horse groups were compared (p < 0.05). Effect sizes were large for the healthy horses' group (ES-1.23) and for the colic horses (ES 0.86), and small to medium for the TMHS horses (ES 0.37). Conclusions: The results of this study show that pain occurs between individual TMHS attacks in severely affected horses and that the quality of life of these horses must be questioned and evaluated individually.
© 2025 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
Publication Date: 2025-04-01 PubMed ID: 40168040PubMed Central: PMC11960477DOI: 10.1111/jvim.70064Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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The research paper is an investigative study into the occurrence and assessment of pain in horses with Trigeminal-Mediated Headshaking (TMHS) during their resting period in between episodes. The authors found that these horses experience significant pain even during their rest periods.
Methods of the Research
The researchers adopted a descriptive study design to evaluate the signs of pain in horses with TMHS at rest, i.e., during periods devoid of typical trigger factors. The investigation involved three sets of horses:
- TWENTY horses diagnosed with TMHS but not presently manifesting active head shaking,
- Twenty horses experiencing moderate gastrointestinal pain caused by colic, and
- Twenty clinically healthy horses, representing a control group.
The Horse Grimace Scale (HGS) was employed to assess horses’ pain level. The HGS is a widely recognized pain evaluation tool designed around horses’ facial expressions.
The process involved recording videos of the horses on two consecutive days, or prior to administering analgesics in the cases of colic horses. Eight photographs were obtained from each video and ranked by three groups of examiners consisting of:
- Veterinary medicine students in their final year,
- Experienced veterinarians not familiar with the HGS, and
- Experienced veterinarians regularly applying the HGS.
To maintain objectivity, all examiner groups were unaware of each horse’s condition.
Results of the Study
The study showed that there were considerable differences in pain levels among the three groups of horses. Healthy horses had the lowest median HGS scores, below 2. TMHS horses generally had a significantly high median HGS score of 5.6. Horses with colic had the highest median scores of 6.6.
These statistics demonstrate that every facial action unit (FAU) scored varied significantly among the different horse groups. The effect sizes were notably large for healthy horses and moderate for horses with colic, while the TMHS horses showed small to medium effect sizes.
Conclusion from the Research
The findings indicated that horses affected by TMHS do suffer some level of pain during their rest periods, between individual TMHS episodes. This insight is central to challenging previous understandings and provokes the need to reevaluate the quality of life of these horses on an individual basis. Each horse’s unique circumstances and pain level should be considered in order to optimize their care and wellbeing.
Cite This Article
APA
Franzen V, Reisbeck D, Leibl Y, Schoster A, May A.
(2025).
Pain Assessment of Horses With Trigeminal-Mediated Headshaking (TMHS) at Rest Between Episodes.
J Vet Intern Med, 39(3), e70064.
https://doi.org/10.1111/jvim.70064 Publication
Researcher Affiliations
- Equine Hospital, Ludwig Maximilians University Munich, Munich, Germany.
- Equine Hospital, Ludwig Maximilians University Munich, Munich, Germany.
- Equine Hospital, Ludwig Maximilians University Munich, Munich, Germany.
- Equine Hospital, Ludwig Maximilians University Munich, Munich, Germany.
- Equine Hospital, Ludwig Maximilians University Munich, Munich, Germany.
MeSH Terms
- Animals
- Horses
- Horse Diseases / diagnosis
- Horse Diseases / physiopathology
- Pain Measurement / veterinary
- Male
- Female
- Colic / veterinary
- Pain / veterinary
- Pain / diagnosis
- Behavior, Animal
Conflict of Interest Statement
The authors have nothing to report. The authors declare no conflicts of interest.
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