Stress biomarkers and stereotypic behaviour in Thoroughbred horses

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 Stereotypic behaviours such as crib-biting and weaving are often seen in horses kept under
restrictive management conditions. These behaviours are repetitive and appear to serve no clear purpose. They are most commonly associated with environments that limit a horse’s ability to meet natural needs, such as continuous foraging, free movement, and social contact. Although stereotypies are widely used as indicators of reduced welfare, the biological processes behind them are not yet fully understood.

In human medicine, stereotypic behaviours are linked to long-term stress and some psychiatric conditions, including obsessive–compulsive disorder. In these cases, saliva is often used to measure stress-related biomarkers because it can be collected easily and without causing discomfort. Similar approaches are increasingly being used in veterinary and equine science research to assess stress in animals.

A study led by Marilena Bazzano, with colleagues from the University of Camerino, Italy, and Sapienza University of Rome, examined whether salivary stress biomarkers differed between Thoroughbred horses with and without stereotypic behaviours. The study focused mainly on horses trained for racing, which are exposed to both physical and mental demands, and included a comparison with non-competing leisure horses.

Cortisol is the most commonly used hormone for measuring stress, as it reflects activation of the hypothalamic–pituitary–adrenal (HPA) axis. However, other salivary markers are now being studied, including alpha-amylase (sAA), which is linked to activity of the sympathetic nervous system, and butyrylcholinesterase (BChE), an enzyme that may also be involved in stress responses. The researchers expected that levels of these biomarkers would vary depending on whether horses showed stereotypic behaviours and whether they were involved in high-level competition.

Saliva samples were collected while the horses were at rest. Three groups of Thoroughbreds were included: ten high-level competition horses without stereotypies, eleven high-level competition horses showing stereotypic behaviours, and five non-competing leisure horses that also showed stereotypies.

The results showed clear differences between the groups. Cortisol levels were highest in the competition horses that did not show stereotypic behaviours. This suggests that the demands of training and competition may increase baseline stress hormone levels, even in horses that appear behaviourally normal.

In contrast, alpha-amylase activity was significantly higher in the non-competing leisure horses with stereotypies. Higher sAA activity is usually linked to increased activation of the sympathetic nervous system, which plays a key role in stress responses. This may indicate that stereotypic horses kept outside of competition experience a different type of stress, possibly related to long-term management or environmental conditions rather than athletic workload.

No significant differences were found in butyrylcholinesterase activity between the groups. This suggests that BChE may be less sensitive to differences in stereotypic behaviour or competition level, at least when measured at rest.

Overall, the study suggests that both competition demands and stereotypic behaviours influence how horses respond to stress at a physiological level. It also shows that using more than one salivary biomarker can provide a clearer picture of equine welfare. However, the authors note that the small number of horses involved and the lack of repeated measurements mean the results should be interpreted with caution.

Despite these limitations, the findings support the use of saliva as a practical, non-invasive method for assessing stress and welfare in horses, and they provide useful direction for future research in equine behaviour and physiology.

For more details, see:

Bazzano M, Marchegiani A, La Gualana F, Petriti B, Petrucelli M, Accorroni L, et al. (2024) Competition and stereotypic behavior in Thoroughbred horses: The value of saliva as a diagnostic marker of stress. 

PLoS ONE 19(10): e0311697. 

https://doi.org/10.1371/journal.pone.0311697

Intra-articular corticosteroids and laminitis risk: new insights into metabolic effects of methylprednisolone acetate

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Intra-articular corticosteroid injections are widely used in equine practice for the management of
joint pain and lameness. Despite their clinical benefits, concerns persist regarding the potential for corticosteroid-induced laminitis, particularly following reports of laminitis developing after joint injections. While many joints are injected safely every year, adverse metabolic consequences appear to be relatively uncommon, raising questions about whether specific corticosteroid formulations, dosages, or patient factors influence risk.

One proposed mechanism for corticosteroid-associated laminitis involves systemic metabolic effects following intra-articular administration. Corticosteroids are known to interact with the hypothalamic-pituitary-adrenal (HPA) axis and may interfere with glucose and insulin metabolism. Disruption of these pathways, particularly the development of hyperinsulinemia, is strongly associated with laminitis. However, not all corticosteroids appear to exert identical metabolic effects, and differences between formulations may be clinically relevant.

To address these concerns, Allen E. Page and colleagues conducted a controlled study at the Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, Martin-Gatton College of Agriculture, Food and Environment, University of Kentucky. The objective of the study was to examine the metabolic effects of intra-articular methylprednisolone acetate (MPA) when administered into multiple low-motion joints.

The study population consisted of six 3-year-old mixed-breed geldings from the university’s research herd. All horses were screened approximately five weeks before the investigation and were confirmed to be free of pituitary pars intermedia dysfunction (PPID) and insulin dysregulation. This ensured that any observed metabolic effects could be attributed to treatment rather than pre-existing endocrine disease.

Each horse was randomly assigned to receive either intra-articular MPA or an equivalent volume of saline. MPA was administered bilaterally into the distal intertarsal and tarsometatarsal joints, with a dose of 20 mg per joint for a total of 80 mg. Serial blood samples were collected to measure resting adrenocorticotropic hormone (ACTH), cortisol, insulin, and glucose concentrations. In addition, repeated low-dose oral sugar tests were performed to assess post-challenge insulin and glucose responses. After a six-week washout period, treatments were crossed over and the protocol was repeated.

The results demonstrated that intra-articular treatment with a total dose of 80 mg of MPA caused significant suppression of the HPA axis. Specifically, resting ACTH and cortisol concentrations were significantly decreased between four and twelve hours following MPA injection. This finding confirms that even intra-articular administration of corticosteroids can produce measurable systemic endocrine effects.

Importantly, however, no significant changes were observed in resting insulin or glucose concentrations. Furthermore, insulin and glucose responses to oral sugar testing at 2, 7, and 14 days post-treatment were not affected by MPA administration. These findings contrast with previous reports involving other intra-articular corticosteroids, which have demonstrated post-injection hyperinsulinemia.

The authors conclude that, in metabolically normal horses, an intra-articular dose of 80 mg of MPA does not appear to induce clinically significant disturbances in insulin or glucose regulation. This observation may help explain the reported practitioner sentiment that MPA carries a lower risk for corticosteroid-induced laminitis compared with other formulations.

Nevertheless, the study’s findings should be interpreted cautiously. The horses involved were young, healthy, and free of known endocrine disease. Additional research is needed to determine whether similar results would be observed in insulin-dysregulated or laminitis-prone horses. Until such data are available, intra-articular MPA should not be assumed to be universally safe in higher-risk populations, despite its apparently favourable metabolic profile in healthy individuals.

  

For more details, see:

Page, A. E., McPeek, J. L., Carattini, S., McGreevy, E., & Adam, E. (2025). 

Intra-articular methylprednisolone acetate does not induce hyperinsulinemia or hyperglycemia in metabolically normal horses. 

Journal of the American Veterinary Medical Association (2025). 

 https://doi.org/10.2460/javma.25.08.0566

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 The 2026 International Society for Equitation Science Conference will take place at the 
LEGOLAND® Conference Centre in Billund, Denmark, from 11–13 August 2026, under the theme “The Nature of Horses.”

Those intending to submit an abstract are encouraged to begin preparations in advance.

Key dates:
• Abstract submissions open: late January / early February 2026
• Abstract submission deadline: 1 March 2026 (final deadline; no extensions)
• Early bird registration closes: 15 May 2026

ISES members are eligible for discounted registration rates.

Further information is available on the ISES conference webpage, with details on registration, keynote speakers, and the full programme to be announced in due course.

For more details, see: 

https://www.equitationscience.com/2026-conference

Effects of simple environmental enrichment on the welfare of stabled horses

Fargo with a jolly ball during research on horse welfare and enrichment 
tools to improve behaviour,healtth and welfare of stabled horses.
(Jael Mackendorf / UC Davis)

Horses evolved to move and forage for much of the day, yet many domesticated horses spend most of their time confined to stalls with limited opportunities for grazing or exploration. This mismatch between natural behaviour and management practices is associated with a range of welfare concerns, including frustration-related behaviours, gastric ulcers, and compromised musculoskeletal health. Recent research from the University of California, Davis, published in the journal Animals, provides evidence that simple, low-cost enrichment strategies can help address these issues in stabled horses.

The study investigated whether common enrichment items (hay feeders, large rubber activity balls, and shatter-proof mirrors) could influence both behaviour and physiological indicators of arousal in competition horses. The work was led by Miranda Brauns during her master’s studies in animal biology at UC Davis, under the supervision of Dr. Amy McLean in the Department of Animal Science and involved collaboration with the UC Davis Intercollegiate Equestrian Team. Ahmed Ali at Clemson University and Jeannine Berger at Sacramento Veterinary Behavior Services also contributed to this research.

The researchers worked with nine stabled American Quarter Horses and American Paint Horses housed at the UC Davis Equestrian Center. Horses were kept in individual stalls within an open-air barn but received daily exercise, including approximately 90 minutes of training and 30 minutes of turnout. Despite this routine, the horses still spent a large proportion of the day confined, particularly between feeding and exercise periods - times when boredom and frustration are likely to peak.

Enrichment items used for the hay feeder, activity ball, and mirror treatments.(c) Brauns et al 

Each horse was fitted with a smart halter capable of continuously recording heart rate and respiration rate, providing insight into physiological arousal and emotional state. Over a four-week period, enrichment items were introduced four times daily in randomised trials. Each session lasted 30 minutes, after which the item was removed. Between different enrichment types, a five-day washout period was used to reduce carryover effects. In total, researchers and student volunteers collected and reviewed around 720 hours of video footage, scoring behaviours such as grazing, locomotion, and frustration-related actions (e.g. stomping, kicking, and tail swishing).

The results showed that enrichment had clear and measurable effects on horse behaviour. Across all item types, horses spent more time engaging in foraging-like behaviours and locomotor movement and showed significant reductions in frustration behaviours compared with control periods without enrichment. These changes were most pronounced during midday and afternoon sessions (around 12:00 and 16:00), when horses did not normally receive feed. This finding suggests that enrichment is particularly valuable during periods of low stimulation between routine meals and exercise.

Physiological data supported the behavioural observations. Enrichment increased heart rate relative to control conditions, indicating heightened arousal and engagement, though respiration rate was not affected. Importantly, the increased heart rate was interpreted not as stress, but as a sign of positive stimulation, especially when accompanied by reduced frustration behaviours. Among the enrichment types, hay feeders produced the strongest overall effects, resulting in activity patterns most like those seen in free-ranging horses. This aligns with the species’ strong motivation to forage for many hours a day. Activity balls also promoted interaction and movement, while mirrors elicited mixed responses: geldings tended to show more interest, whereas mares were more likely to avoid them. Mirrors were also associated with lower evening heart rates compared with other times of day, suggesting a calming effect in some contexts.

From an applied perspective, the findings highlight the potential for simple enrichment tools to improve equine welfare without major changes to housing systems. By providing enrichment, particularly forage-based options, during times when horses are otherwise inactive, owners and managers may reduce boredom-related behaviours and support both mental and physical health. The authors emphasise that enrichment does not replace turnout or exercise but serves as an important additional management tool.

While the study involved a relatively small number of horses and short-term trials, it reinforces the importance of aligning management practices with species-typical behaviours and suggests that even modest interventions can have meaningful welfare benefits. Further research with larger populations and longer time frames will be needed to assess long-term impacts and refine recommendations for different enrichment types.

For more details, see: 

Brauns, Miranda, Ahmed Ali, Jeannine Berger, and Amy McLean. 

Physiological and Behavioral Responses of Stabled Horses (Equus caballus) to Three Types of Environmental Enrichment

Animals (2025) 15, no. 19: 2779. 

https://doi.org/10.3390/ani15192779

Ageing, blood supply and tendon health: new research

Photo: RVC

 Tendon injuries are one of the most common causes of lameness and loss of performance in
horses, particularly as they get older. 

A new study from the Royal Veterinary College (RVC) has shed important light on why ageing tendons are more vulnerable to injury and slower to heal, by closely examining how the tendon’s blood supply changes with age.

 

Tendons are specialised tissues that transmit force from muscle to bone. To do this efficiently, they are dense and tightly packed with collagen fibres. While this structure is excellent for strength and elasticity, it comes at a cost: tendons have relatively few cells and a limited blood supply compared with other tissues.

 

Blood vessels are vital for delivering oxygen and nutrients, removing waste products and supporting repair after microscopic damage caused by normal exercise. Because tendons are already poorly supplied with blood, any further reduction can seriously limit their ability to maintain healthy tissue and to heal after injury.

 

The study focused on the superficial digital flexor tendon (SDFT) in horses. This tendon is frequently injured in athletic horses and is considered the functional equivalent of the human Achilles tendon. This makes the horse an excellent model for understanding tendon ageing in both veterinary and human medicine.

 

The research team, led by Dr Nodoka Iwasaki, Postdoctoral Researcher, and Dr Chavaunne Thorpe, Lecturer in Basic Sciences at the RVC’s Department of Comparative Biomedical Sciences, used advanced 3D technologies (micro-computed tomography (μCT) and confocal microscopy) to capture detailed images of tendon tissue from young (2-5 years old) and older (18-22 years old) horses, enabling them to visualise and quantify the tendon’s vascular network in unprecedented detail. 

 

This approach allowed the researchers to map the tendon’s microvasculature in unprecedented detail.

 

The μCT analysis showed striking age-related changes in the tendon’s blood vessels, particularly within the interfascicular matrix (IFM)  (the region between tendon fibre bundles that is important for tendon elasticity and repair.)

 

In older horses, compared with younger ones, there was:

·      70% reduction in total vascular volume

·      30% reduction in average vessel diameter

·      74% reduction in vessel density

 

In simple terms, older tendons had far fewer and smaller large blood vessels. This leads to significantly reduced blood flow, helping to explain why older tendons are more prone to degeneration and slower to heal.

 

At the same time, the immunolabelling studies revealed something unexpected. Markers associated with endothelial cells (cells lining blood vessels, identified using von Willebrand factor, VWF) and pericytes (support cells that stabilise small blood vessels ) were increased in aged tendons. 

 

This suggests that new, very small blood vessels (capillaries) are forming. However, these new vessels appeared disorganised and were not accompanied by healthy larger vessels. The researchers also found major reductions in markers associated with mature, functional vessel walls (such as MYH11 and desmin), indicating a loss of normal vascular structure.

 

Taken together, the results suggest that ageing tendons lose their well-organised, larger blood vessels and attempt to compensate by forming many small, immature vessels.

 

This disorganised angiogenesis may be driven by low-level inflammation or repeated micro-damage over the horse’s lifetime, but further research is needed to confirm this.

 

Crucially, these new small vessels may not function effectively, meaning they do not adequately restore blood flow or support proper healing.

 

This research helps explain several real-world observations:

·      Older horses are at higher risk of tendon injury

·      Tendon injuries in older horses heal more slowly

·      Re-injury rates are high due to poor-quality repair and scar tissue formation

 

Understanding these vascular changes may help:

·      Identify horses at higher risk of injury

·      Tailor training and workload more carefully as horses age

·      Improve rehabilitation strategies by recognising the limits of tendon healing in older animals

 

By identifying specific age-related changes in tendon blood vessels, this study opens the door to new therapeutic approaches. Potential future strategies may aim to:

·      Preserve healthy blood vessels as horses age

·      Improve vascular organisation during tendon healing

·      Enhance regeneration rather than scar formation

 

Such advances could significantly improve outcomes for older horses with tendon injuries and may also translate to better treatments for tendon injuries in people.

 

In summary, this study provides the first detailed 3D picture of how tendon blood supply changes with age. It shows that while older tendons try to adapt, the loss of healthy, functional blood vessels is likely a key reason why ageing tendons are more fragile and slower to heal.

 

For more details, see: 

 

Nodoka Iwasaki, Jack Llewellyn, Jeanne Brown, Danae E. Zamboulis, Elizabeth J. T. Finding, Caroline P. D. Wheeler-Jones, Chavaunne T. Thorpe

Immunolabelling and Micro-Computed Tomography Revealed Age-Related Alterations in 3D Microvasculature of Tendons.

 Aging Cell (2025) e70293.

https://doi.org/10.1111/acel.70293

RVC launches major study to reduce training-related injuries in Thoroughbred racehorses

(c) Paul Curry Dreamtime.com

Researchers at the Royal Veterinary College (RVC) have launched a large-scale research
programme aimed at improving the safety and welfare of Thoroughbred racehorses during training. The Training Injury Prevention Study seeks to address a significant gap in current knowledge by focusing on musculoskeletal injuries (MSI) that occur away from the racecourse,

While substantial progress has been made in understanding race-day injuries, far less is known about injuries sustained during daily training, despite these injuries being a leading cause of morbidity and mortality in racehorses worldwide.

This lack of evidence has limited the ability of trainers, veterinarians, and regulators to identify horses at risk and implement effective preventative strategies. The new study aims to provide robust, data-driven evidence to support safer training practices and improve long-term welfare outcomes.

The project is funded by the Horserace Betting Levy Board and the Racing Foundation, with endorsement from the British Horseracing Authority. It aligns closely with the Horse Welfare Board’s Best Possible Safety strategy, contributing to broader industry goals around welfare, sustainability, and public confidence in British racing.

Over a three-year period, the research team will conduct prospective cohort studies involving both flat and National Hunt (jump) Thoroughbreds in training across Great Britain. By following horses over time, the researchers will be able to estimate the incidence of common training-related musculoskeletal injuries, including fractures and tendon and joint injuries. This approach will allow injury occurrence to be linked directly to training practices and workloads.

A central component of the study is the development of novel measures of training workload. Currently, there is little documented evidence describing how racehorses are trained in practice or how variations in workload influence injury risk. By quantifying training intensity and volume, the researchers aim to identify modifiable risk factors associated with exercise-induced injury and determine how training regimes can be optimised to reduce harm.

The project will also trial the use of wearable GPS technology to assess its practicality for large-scale use within the racing industry. These devices will be used to measure parameters such as speed, distance, stride frequency, and stride length, providing objective data to estimate training workloads more accurately over time.

Professor Kristien Verheyen, Professor of Veterinary Clinical Epidemiology at the RVC, emphasised the importance of the work, noting that the study will fill critical knowledge gaps regarding injury occurrence in training. The findings are expected to support evidence-based interventions and highlight examples of best practice within current training systems.

Overall, the Training Injury Prevention Study aims to generate the scientific evidence needed to reduce the risk of musculoskeletal injury in Thoroughbred racehorses, improving welfare outcomes while supporting the long-term sustainability and social licence of the racing industry.

The research team encouraged age rracehorse trainers interested in taking part in this study to register their no obligation express of interest, here.

For more information about the Training Injury Prevention Study, see:

https://www.rvc.ac.uk/research/projects/training-injury-prevention-study.