Stress in young sport horses during breaking-in

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Sport horses are frequently exposed to a variety of stressors throughout their careers—including training, transportation, and competition—all of which can trigger elevated cortisol release, a
well-known marker of stress. While numerous studies have explored the impact of these stressors on adult performance horses, relatively little attention has been paid to the early stages of a horse’s career, particularly the breaking-in period. Yet this is a critical transition that can have lasting effects on welfare, behaviour, and long-term performance. 

A recent study conducted by Julia Krieber and colleagues at the University of Veterinary Medicine, Vienna, sought to fill this gap by investigating the physiological stress response in young horses as they progress from unridden status into ridden work. A full report of the work is published in Animals.

 

The study was carried out on 41 horses from a single stud farm, ranging in age from 1 to 20 years. 

Based on their training status, the horses were categorized into two main groups:

• Unridden horses (n = 28): This group included warmbloods (both mares, stallions, and geldings), Haflingers, and one Noriker. These horses had no experience under saddle but were halter trained and accustomed to regular human interaction since birth. They were kept in open stables with seasonal access to paddocks. Their barns were bedded with straw using a deep litter system, which was typically cleaned every two weeks—a setup intended to reflect a more natural, group-based housing environment.
• Horses in training (n = 13): All were warmblood geldings, housed individually in box stalls. These horses were undergoing various stages of formal ridden training, including the initial breaking-in period.

 

The researchers measured faecal cortisol metabolites (FCMs) from all horses—an established, non-invasive method for assessing chronic stress levels in animals. FCMs provide a longer-term view of physiological stress compared to blood sampling, which can itself be stressful for the animal.

 

The results revealed important insights into how the onset of training impacts stress levels:

Unridden horses had significantly lower FCM concentrations compared to horses in training (Mann-Whitney rank sum test, p < 0.001), suggesting that the training process is a major source of stress.

Among horses in training, those in their first year under saddle showed especially elevated FCM levels when compared to unridden peers (ANOVA with Holm-Sidak post hoc test, p < 0.05). This confirms that the breaking-in phase is particularly stressful, likely due to new physical and psychological demands.

 

FCM levels tended to decrease over time with continued training, indicating some degree of habituation or adaptation to the work, although this varied by individual.

 

Within the training group, there was a wide variability in FCM concentrations, suggesting that horses respond differently to the same training conditions. This variability may reflect individual temperament, previous experiences, or coping styles.

 

This study reinforces the notion that breaking-in represents a critical and potentially stressful milestone in a young horse’s life. The findings carry several important implications:

• Tailored training approaches are essential. Given the observed individual variability in stress responses, trainers should adapt their methods based on the horse's behavior, temperament, and rate of progress.
• Management practices influence stress. Differences in housing conditions—group housing with paddocks versus individual boxes—may contribute to overall stress levels and coping ability, though this variable was not the central focus of the study.
• Gentle and progressive introduction to ridden work is key. Minimising psychological and physical stress during early training can improve welfare and potentially enhance long-term performance and trainability.
• Monitoring welfare through physiological indicators like FCMs can provide valuable insights into how horses experience their environment and training regime.

 

The findings by Krieber and colleagues highlight an often-overlooked aspect of equine welfare: the impact of early training on stress levels in young horses. By demonstrating that horses experience significantly increased stress during the initial stages of being backed and ridden, the study underscores the importance of empathetic, evidence-based approaches to breaking-in.

 

In a field where performance is often the focus, it is essential not to overlook the horse's mental and emotional well-being; especially at the very start of their careers. As this research shows, how we introduce horses to training matters; not only for their welfare but for their future success as sport partners.

 

For more details, see:

 

Krieber, Julia, Aurelia C. Nowak, Jakob Geissberger, Oliver Illichmann, Sabine Macho-Maschler, Rupert Palme, and Franziska Dengler. (2025). 

"Fecal Cortisol Metabolites Indicate Increased Stress Levels in Horses During Breaking-In: A Pilot Study" 

Animals 15, no. 12: 1693. 

https://doi.org/10.3390/ani15121693

Investigating the relationship between headshaking and the hyoid apparatus in horses: A CT-based study

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Headshaking in horses is a frustrating and often debilitating condition that can significantly
impact welfare and performance. Most commonly, it presents as sudden, repetitive, and often violent vertical or horizontal movements of the head, sometimes accompanied by snorting, rubbing the muzzle, or signs of facial pain. In many cases, headshaking is considered idiopathic, but it is frequently associated with trigeminal-mediated neuropathic pain - meaning the horse perceives abnormal, often painful, sensations due to dysfunction of the trigeminal nerve.

Because clinical signs can mimic discomfort arising from other sources, diagnostic work-ups for headshaking often include advanced imaging techniques such as computed tomography (CT) of the skull. These scans aim to identify or rule out structural abnormalities that may be contributing to the signs.

 

One anatomical area of interest is the hyoid apparatus, a complex chain of small bones that supports the tongue and larynx and connects to the base of the skull via the temporo-hyoid joint. The hyoid plays a critical role in swallowing, vocalisation, and possibly in movement coordination between the head and neck. It is anatomically and functionally close to the ear and cranial nerves, including the trigeminal nerve, raising the question: could hyoid apparatus pathology contribute to headshaking?

 

To explore this possibility, Ralph Lloyd-Edwards and colleagues conducted a retrospective study to assess CT changes in the hyoid apparatus of horses. 

 

All horses that were referred to the Diagnostic Imaging Division, Department of Clinical Sciences of the Veterinary Teaching Hospital, in the Faculty of Veterinary Medicine of Utrecht University with reported clinical signs consistent with headshaking between February 2015 and June 2022 were included in the study.

 

The researchers compared a group of horses showing clinical signs of headshaking to a control population with no history of headshaking. Additionally, a subgroup of headshakers with no other identifiable causes (e.g. sinus disease, dental issues, or ear pathology) was compared to controls, to evaluate whether hyoid changes might be more significant in otherwise unexplained cases.

 

Several anatomical changes were documented via CT, including:

 

• Temporohyoid joint sheath ossification – a thickening and bony change in the connective tissue surrounding the joint.

• Mineralisation of the tympanohyoid cartilage – hardening of the cartilage connecting the hyoid to the temporal bone.

• Joint space alterations – either narrowing or widening of the temporohyoid joint space. 

• Structural abnormalities – such as deformation, fracture, or degenerative joint changes within the hyoid bones.

 

These changes were found to correlate significantly with age - older horses were more likely to show ossification and other degenerative features. Additionally, the degree of change in one area of the hyoid often correlated with changes in adjacent structures, suggesting a progressive or systemic pattern of bony adaptation.

 

Interestingly, centres of ossification were also described in smaller hyoid bones, including the epihyoid, thyrohyoid, and the lingual process of the basihyoid, highlighting the complex and variable anatomy of this region.

 

Despite some initial trends - especially in the subgroup of horses with no other obvious cause for headshaking-  no consistent or statistically significant association was found between hyoid apparatus abnormalities and clinical signs of headshaking. While odds ratios for certain changes were elevated in headshakers, they did not reach levels that would support a causal link.

 

CT imaging of the hyoid apparatus reveals a wide range of anatomical variations and age-related changes, but these findings do not appear to be directly or consistently linked to headshaking in horses. While it remains possible that in certain cases hyoid abnormalities could contribute to or exacerbate discomfort, particularly in horses with concurrent trigeminal sensitivity, this study did not establish a clear diagnostic or therapeutic target in the hyoid region for managing headshaking.

 

For horse owners and equine professionals, this study underscores the complexity of diagnosing headshaking and highlights the importance of a comprehensive work-up. While CT can be valuable for ruling out other structural causes, hyoid changes should be interpreted cautiously and within the broader clinical context.

 

 

For more details, see:

 

Lloyd-Edwards, Ralph A., Eva Mulders, Marianne M. Sloet van Oldruitenborgh-Oosterbaan, and Stefanie Veraa. 2025. 

Computed Tomography of the Hyoid Apparatus in Equine Headshaking Syndrome

Veterinary Sciences 12, no. 6: 511. 

https://doi.org/10.3390/vetsci12060511

UF researchers seeking Central Florida horses for arthritis pain study

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 Do you own a horse with osteoarthritis, especially in the fetlock joint? Researchers at the
University of Florida are inviting horse owners to take part in a new study that could lead to better ways of identifying and managing joint pain — both in horses and in humans.

This research effort is a collaboration between UF’s Institute of Food and Agricultural Sciences (UF/IFAS), the UF College of Veterinary Medicine, the UF College of Dentistry, and the UF Department of Biomedical Engineering. Their goal is to improve how veterinarians detect joint pain in horses before it becomes visibly severe — giving your horse a better shot at long-term joint health and comfort.

Osteoarthritis is a leading cause of lameness and discomfort in horses. Like humans, horses develop arthritis from repetitive stress on the joints — often due to performance activities like racing, jumping, or even frequent trail work. While joint pain in horses is common, it's often not diagnosed until the horse shows clear signs of discomfort. By that point, valuable joint function may already be lost.

Dr. Samantha Brooks, associate professor of equine physiology and genetics at UF/IFAS, says this new study uses a non-invasive screening process designed to catch signs of pain earlier and more objectively than traditional evaluations.

“We tend to treat symptomatically when horses show obvious clinical signs of pain, but if we can detect subtle joint pain sooner, we might be able to start pain treatments in time to better preserve joint function, and tailor that treatment for each horse,” Brooks said. “And our horses undergo a lot of the same joint diseases that we have. Any tools that we can build to better understand the discomfort caused by arthritis in horses gives us a better understanding of arthritis pain in people.”

Because horses can’t tell us when or where it hurts, the UF team is aiming to build a more accurate way to assess pain — something that could ultimately improve not only equine care but also the way doctors understand arthritis pain in humans.

For this field study, UF is recruiting horses already diagnosed with osteoarthritis — ideally in the fetlock joint — who live in Central Florida. Horses enrolled in the study will receive a free initial screening, which includes:

• A basic lameness exam (e.g., walk/trot in a straight line)

• Radiographs (X-rays) of the fetlocks

• A simple blood draw

After the initial evaluation, the research team will make follow-up visits a few times a year over a two-year period. These visits are designed to observe the horses in their usual environment — there’s no change expected in your horse’s routine. Researchers will track movement patterns and behaviors using new, non-invasive technologies to better understand the signs of discomfort.

Kaylee Young, research coordinator in UF’s Animal Sciences department, emphasized how important horse owners are to this work.

“Participating in this study could lead to better pain management and care for not only our horse companions but for people,” she said. “This research could be something that could be life changing not only for horses but for humans.”

Interested in participating?
If your horse meets the criteria and you’d like to be part of this important study, email uf-gallop@ufl.edu with the subject line “Study Participation.” Be sure to include your location and a few details about your horse’s health, including whether they’ve been diagnosed with fetlock osteoarthritis.

Morris Animal Foundation offers funding for research projects

 Morris Animal Foundation, one of the largest non-profit animal health research organisations in the world, is now inviting requests for research proposals to improve the health and welfare of domesticated horses, ponies, donkeys and mules. 

This opportunity includes four award categories — Established Investigator, First Award, Pilot Study and Fellowship Training — each designed to support impactful, humane, and scientifically robust equid health research.  

On offer are grants of up to $145,000 over 24 months,  depending on category.

All applicants must clearly describe the health problem their research addresses and its significance, demonstrate their qualifications and outline a sound scientific approach, and assess the environmental and animal welfare impacts of their study. Proposals must also include appropriate sample size calculations, ethical research design considerations, and a fully justified budget using the Foundation’s provided templates.  

Applicants must submit proposals via the Foundation’s online portal by 4:59 p.m. ET, August 6, 2025.Full details and templates are available on the Foundation’s Grants page.  

https://www.morrisanimalfoundation.org/apply