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

Ongoing work to improve racehorse safety - Free articles

 The Equine Veterinary Journal (EVJ) has highlighted the global commitment to enhancing racehorse welfare by releasing a special open-access collection focused on racehorse safety. This curated selection of peer-reviewed research stems from the 2024 International Federation of Horseracing Authorities (IFHA) Global Summit on Equine Safety and Technology, an event that brought together leading experts to address some of the sport's most pressing health concerns.

The summit assembled a diverse group, including research scientists, equine clinicians, veterinarians, and racing regulators, from around the world. Together, they examined how cutting-edge science and emerging technologies could be applied to reduce the risk of catastrophic injuries such as bone fractures and exercise-associated sudden death in racehorses.

This special EVJ collection includes four editorials inspired by key themes and discussions from the summit, along with 22 additional research articles. Topics range from advances in diagnostic imaging and track surface analysis to genetic and physiological studies aimed at improving risk prediction and management.

In addition to the published research, a related podcast is also available, featuring a discussion with several summit leaders. The podcast offers further insight into the collaborative strategies and innovative tools being developed to make racing safer for horses worldwide.

This initiative underscores a global shift towards evidence-based practices in equine sports and reflects an ongoing dedication to the welfare of racehorses through collaborative scientific advancement.

The special collection, which includes four editorials based on the summit along with 22 additional papers, is available here:

https://beva.onlinelibrary.wiley.com/doi/toc/10.1001/(ISSN)2042-3306.racehorse-safety

A related podcast featuring discussion among several principals of the IFHA summit is available here:  

https://evj.podbean.com/e/evj-in-conversation-podcast-no-87-june-2025-jamie-stier-chris-riggs-celia-marr-rhiannon-morgan/

Correlation between mild changes on back radiographs and performance

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 Mild radiographic abnormalities of the thoracolumbar spinous processes do not necessarily impair performance in warmblood jumping horses.

Back pain is a well-recognised contributor to reduced performance in sport horses. However, the precise relationship between clinical signs of back discomfort and radiographic abnormalities of the spine remains poorly defined.

A recent descriptive observational study, published in the Journal of Equine Veterinary Science, aimed to characterise radiographic findings of the thoracolumbar spinous processes in actively competing Warmblood show jumpers and to assess any associations with performance outcomes.

The study evaluated 100 Warmblood jumping horses, all competing in 2018, with a median fence height of 1.35 m (mean 1.3 m; range 0.90–1.60 m). All horses included were free from observable lameness and neurological deficits. Lateral radiographs of the thoracolumbar spine were obtained and assessed by four independent observers, who graded each image for the presence and severity (absent, mild, moderate-to-severe) of four specific abnormalities: narrowed interspinous spaces, sclerosis, lucency, and enthesopathy.

Inter-observer agreement was assessed using the Intraclass Correlation Coefficient (ICC), revealing moderate to good consistency across observers.

In addition to radiographic evaluation, signalment, years of competition, current level of performance, and highest career performance level were recorded for each horse. These variables were then analysed for correlation with radiographic findings.

Strikingly, no horse in the study population was entirely free from radiographic abnormalities, highlighting the high prevalence of such changes among active sport horses. Narrowed interspinous spaces and sclerosis were the most commonly observed findings, predominantly located between thoracic vertebrae T15 and lumbar vertebra L1. Enthesopathy was most frequently identified at the withers, specifically between T8 and T13.

Despite the high prevalence of abnormalities, the research team found no significant correlations between radiographic changes and the horse's age, current performance level, or total years of competition (p > 0.05). Interestingly, the highest career performance level showed a weak but statistically significant positive correlation with the presence of narrowed interspinous spaces and sclerosis. These findings suggest that some radiographic abnormalities may not only be tolerated by high-performing horses but could also reflect adaptive or age-related changes without clinical relevance.

In conclusion, mild radiographic changes of the thoracolumbar spinous processes—particularly narrowing of interspinous spaces and sclerosis—were commonly observed in this cohort of active Warmblood jumpers. Importantly, these findings were not associated with impaired performance, indicating that such abnormalities, when mild and absent of clinical signs, may not adversely impact athletic function.

 

For more details, see:

 

M.P. Kerbert, S.S. le Jeune, K.L. Philips, K.L. Shaw, C.A. Erickson, P. Espinosa-Mur,

Mild radiographic abnormalities of thoracolumbar spinous processes are not associated with decreased performance in 100 Warmblood jumping horses in active competition,

Journal of Equine Veterinary Science,(2025)

Vol 147, 105366,           

https://doi.org/10.1016/j.jevs.2025.105366

Ethogram for understanding horse emotions and social behaviour

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 Researchers at the University of Portsmouth’s Centre for Comparative and Evolutionary Psychology have developed the first anatomically-based ethogram of equine facial behaviour, offering a tool for understanding how horses communicate through facial movements. This ethogram—essentially a structured catalogue of facial actions—captures how domestic horses use their faces to convey emotions such as curiosity, aggression, playfulness, and attentiveness across a variety of social contexts.

Unlike the term “facial expression,” which often implies an associated emotion, the researchers have deliberately used the term facial behaviour. This distinction acknowledges that while some facial movements may correlate with emotional states, not all facial changes are necessarily expressive in the emotional sense. This neutral terminology allows for more objective observation and coding of equine facial movements.

 

The aim of the study was to develop an ethogram of equine facial behaviour observed during horse-horse interactions. These interactions were categorised into affiliative (non-play), play, agonistic (conflict), and attentional contexts. Using the Equine Facial Action Coding System (EquiFACS)—an established method that links visible facial changes to specific underlying muscle movements—the researchers documented 805 facial expressions across 22 distinct behaviours.

 

Crucially, they employed a novel statistical tool to analyse how these facial actions cluster in different social scenarios, providing new insights into the functional roles of facial behaviour in equine communication.

 

The study revealed that horses exhibit a wide and nuanced range of facial behaviours depending on the social context:

 

Agonistic Interactions
Aggressive or conflict-based interactions were marked by flattened, backward-facing ears, inner brow raisings, nostril dilation, and head-lowering. These signals offer clear warnings of potential escalation, helping horses (and human observers) anticipate and de-escalate conflict.

 

Attentional States
When alert or investigating their environment, horses displayed forward-pointing, closely positioned ears. Additional markers included increased blinking or half-blinking, and head positions that facilitated sensory focus, such as lifting the head to enhance visual attention.

 

Friendly Interactions
Interestingly, affiliative interactions were often characterised by relatively neutral facial behaviour. Contrary to the common belief that ears forward indicate positive emotion, this was not consistently observed. This suggests that minimal facial movement in these contexts may actually signal comfort and positive mood—highlighting the importance of considering the broader behavioural and social context.

 

Play Behaviour
Playful interactions involved the most dynamic facial displays, including dropped lower lips, raised chins, parted lips, open mouths, flattened or rotated ears, prominent eye whites, and forward-thrust nostrils. Many of these expressions resemble the open-mouth play faces seen in primates and carnivores, supporting the idea of a shared evolutionary origin for certain play behaviours across mammalian species.

 

“We found that horses often use the same facial movements across different contexts, but the combinations and intensities vary,” explained Dr Kate Lewis, lead author. “This flexibility underscores the importance of considering the whole body and context when interpreting equine behaviour.”

 

One of the most intriguing findings was the identification of a previously unrecorded facial movement, designated as AUH21, involving the platysma muscle. (The platysma muscle  is a thin, superficial muscle located just beneath the skin. It extends along the side of the face and neck, originating from the region near the ear and inserting into the skin of the neck and shoulder. Its primary function is to move the skin, aiding in facial expressions and helping to twitch the skin to repel insects.)This movement causes tightening on the side of the face, making the underlying anatomical structures more visible. AUH21 has previously only been documented in humans and gibbons, making its discovery in horses significant for comparative biology. It may also offer new avenues for evaluating emotional states and pain indicators in equine clinical settings.

 

By providing a scientifically validated reference for interpreting equine facial behaviour, the ethogram is poised to become a vital resource for equine veterinarians, behaviourists, trainers, and students of equine science.

 

“This is the first time we’ve been able to systematically document how horses combine facial movements into meaningful expressions,” said Dr Leanne Proops, Associate Professor in Animal Behaviour and Welfare. “It opens up new possibilities for understanding equine emotions and improving welfare.”

 

The study is published in PeerJ, along with the full ethogram and supporting analyses, offering a robust framework for further research and practical application.

 

“This work is a game-changer for anyone working with horses,” Dr Proops added. “It gives us a new lens through which to view and interpret their behaviour, ultimately leading to better care and stronger human-animal relationships.”

 

For more details, see: 

 

Lewis K, McBride SD, Micheletta J, Parker MO, Rincon AV, Wathan J, Proops L.(2025). 

An ethogram of facial behaviour in domestic horses: evolutionary perspectives on form and function. 

PeerJ 13:e19309

https://doi.org/10.7717/peerj.19309

Impact of turnout rugs on horse behaviour: a study under mild weather conditions

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Rugging horses is a widespread practice, commonly used to keep them warm and dry in cold, wet weather or to protect them from insects and sunlight in warmer conditions. However, rugs may also pose drawbacks — potentially causing thermal discomfort or restricting natural behaviours such as grooming and movement.

Despite the routine use of rugs, especially in the UK where spring and autumn bring relatively moderate weather, few studies have examined how horses behave with and without rugs in such conditions. A recent study by Frederick Daw and colleagues at the Royal Veterinary College, London, aimed to address this gap. The research, published in Applied Animal Behaviour Science, provides evidence that can help owners make more informed decisions about rug use to support equine welfare.

The study involved ten healthy horses, all accustomed to wearing rugs, from two different yards in southern England. Each horse was observed during 30-minute sessions, with and without a turnout rug, across several weeks. A total of 172 observation sessions were carried out, ensuring that each horse experienced both conditions in roughly equal measure.

Weather conditions during the study ranged from 1°C to 15°C, with wind speeds of 6 to 15 mph. Importantly, no signs of heat or cold stress were noted in any horse throughout the study period. The researchers analysed behavioural data using Generalised Estimating Equations (GEE), a statistical method that accounts for repeated measures on the same individuals.

The results showed a mix of both positive and negative effects associated with rugging:

·       Reduced insect-related behaviour: Horses wearing rugs exhibited significantly less tail swishing and head shaking, behaviours commonly linked to fly or midge irritation. Midges (Culicoides spp.) were observed at both sites, particularly when temperatures were higher and winds lower - conditions known to favour insect activity. These findings suggest that turnout rugs may offer effective protection against insect harassment under mild weather conditions.

·       Increased grazing at one site: At one of the two study locations, rugged horses spent more time grazing. This may reflect reduced fly irritation or increased comfort when wearing rugs.

However, the study also highlighted potential concerns:

·       Reduced movement and grooming: Horses wearing rugs were observed to walk less and perform fewer self-grooming behaviours. Both activities are considered important for physical health and psychological well-being. Their reduction may indicate that the rugs, though protective, imposed some physical restriction or discomfort  - possibly due to their weight or design.

·       Site-specific differences: The effects of rugging varied significantly between the two locations, suggesting that environmental factors and management practices also influence how horses respond to being rugged. Therefore, caution is needed when generalising these findings to other settings.

Tail swishing was found to increase with temperature (by 1.33 swishes per 1°C) and decrease with windspeed (by 0.84 swishes per 1 mph). These results further support the conclusion that environmental conditions - particularly warmth and still air - are key drivers of insect-related behaviours in horses.

This study indicates that during mild weather conditions (above 5°C), lightweight turnout rugs may help reduce insect-related discomfort in horses. However, rug choice matters: heavier or poorly fitting rugs may inhibit natural behaviour, outweighing any protective benefits.

The researchers conclude:

“When weather conditions are relatively mild (above 5 °C), horse welfare may be improved more by the use of lightweight turnout rugs for fly protection rather than heavyweight rugs designed primarily for warmth.”

They also call for further studies to test this idea more directly — in particular, by assessing the impact of purpose-designed fly rugs under mild autumn conditions, as opposed to standard waterproof turnout rugs.

For more details, see:

 

Frederick Daw, Charlotte Burn, Yu-Mei Chang, Christine Nicol,

Effect of turnout rugs on the behaviour of horses under mild autumn conditions in the United Kingdom,

Applied Animal Behaviour Science, (2025) vol 288,106661

 

https://doi.org/10.1016/j.applanim.2025.106661