The horse who collapses during tacking up can be a real worry, and this an issue that particularly interests me. I’ve come across a handful of horses in my career who have shown this behaviour. From the research that I’ve done, there are very few studies into this. The information that I’ve come across leads me to think that this behaviour in horses is due to something called ‘neurocardiogenic syncope’, or ‘neural syncope’, or ‘vasovagal syncope’.
A recent webinar by Dr Joseph Bertone, a vet who is an expert in sleep disorders in horses. The webinar was hosted by the Equine Behaviour and Training Association, and it got me thinking about it again. Dr Bertone started the webinar with a video of a horse showing extremely ‘sleepy’ behaviour after he was tacked up. He invited questions, and so I’ve emailed him to ask his thoughts on neurocardiogenic syncope, and how this might or might not be linked to sleep disorders. If you’re interested in finding out more about sleep disorders in horses, here is an article by Dr Bertone titled ‘Six Types Of Sleep Deprivation In Horses’.
One of the few places on the internet that I’ve seen neurocardiogenic syncope in horses mentioned is this short piece, by Michelle Abraham Linton BSc BVMS DACVIM LAIM. I have contacted Michelle to ask for more information, and will let you know if I hear back from her.
In terms of research on neurocardiogenic syncope in horses, I’ve been able to find very little, but I wanted to share with you the study below. This was a retrospective study (which means they looked back at past records) of horses seen between 1995 and 2009 at the Dick Vet Equine Hospital. They found 25 cases of collapsing horses who were referred to the vet, some of whom collapsed just once, others collapsed many times. Of these 25 horses, five were given a presumptive diagnosis (which means they don’t have any definitive way of diagnosing, so they make a best guess) of neurocardiogenic syncope. Unsurprisingly, the conclusion was that it was easier to get a definitive diagnosis in a horse which collapsed multiple times.
My recommendation for managing a horse who goes sleepy or partially collapses when tacked up is first of all to contact the vet to rule out any serious concerns. If the vet is happy that it’s safe to keep working with the horse, then I suggest finding a way of allowing the horse to move a little during the tacking up process. Safety is always the top priority, and you are responsible for the safety of yourself, your horse, and others around you and your horse.
Interestingly, there is low level evidence that this is effective in managing vasovagal syncope in humans. This review looked at studies that had used change of body position or physical counter-pressure manoeuvres to prevent the faint.
Background: Episodic collapse in horses has equine welfare and human safety implications. There are, however, no published case series describing this syndrome.
Objectives: To characterize the cause and outcomes for horses referred for investigation of episodic collapse.
Animals: Twenty-five horses referred for investigation of single or multiple episodes of collapse.
Methods: Retrospective study. Clinical records from the Dick Vet Equine Hospital, University of Edinburgh from November 1995 to July 2009 were searched using the following keywords: collapse, collapsing, fall, syncope. Collapse was defined as an incident in which the horse lost postural tone with or without progression to recumbency and with or without loss of consciousness. Long-term follow-up information was obtained by telephone conversation with the owner.
Results: A final diagnosis was reached in 11 cases, namely cardiac arrhythmia (4), right-sided heart failure (1), hypoglycemia (2), generalized seizures (2), and sleep disorder (2). A presumptive diagnosis was reached in 8 cases, namely neurocardiogenic syncope (5), exercise-induced pulmonary hemorrhage (2), and generalized seizures (1). No diagnosis was reached in 6 cases despite comprehensive investigations. Three horses were euthanized at presentation. Treatment was attempted in 9 horses with 6 cases having successful outcome before discharge. Follow-up information was available for 14 of 19 horses discharged from the hospital. Only 1 of these horses was observed to collapse after discharge.
Conclusions and clinical importance: Definitive diagnosis was more likely to be reached in cases with multiple episodes of collapse. Horses in which 1 episode of collapse occurred did not necessarily collapse again.
Lyle CH, Turley G, Blissitt KJ, Pirie RS, Mayhew IG, McGorum BC, Keen JA. Retrospective evaluation of episodic collapse in the horse in a referred population: 25 cases (1995-2009). J Vet Intern Med. 2010 Nov-Dec;24(6):1498-502. doi: 10.1111/j.1939-1676.2010.0610.x. Epub 2010 Oct 12. PMID: 21039868.
You can read this study in full here.
© Sue Palmer, The Horse Physio, 2021
Treating your horse with care, connection, curiosity and compassion
