Transient hindlimb asymmetry following intramuscular vaccination in horses

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Vaccination is an essential part of preventative healthcare in horses and plays a major role in
protecting equine populations from infectious diseases such as influenza and tetanus. Most vaccines are administered by intramuscular injection, meaning the vaccine is delivered directly into a muscle. Although vaccination is considered safe and routine, mild side effects can occasionally occur.

 

A recent study investigated whether intramuscular vaccination into either the semitendinosus muscle or the pectoralis descendens muscle could temporarily affect a horse’s movement and gait.

 

The semitendinosus is one of the large muscles located in the horse’s hindquarters. It forms part of the hamstring muscle group and contributes to propulsion during movement, particularly when the horse pushes off the ground during walking, trotting, or cantering. Because of its size and accessibility, this muscle is sometimes used as an injection site for vaccines or medications.   The pectoralis descendens (also known as the cranial superficial pectoral muscle) forms part of the ‘thoracic sling’ between the front legs that supports the torso. It is a common site for intra-muscular Injections.

 

The study found that routine intramuscular vaccination into the semitendinosus  resulted  in a “transient, measurable push-off-type hindlimb asymmetry.” In simpler terms, the vaccinated horses showed a temporary unevenness in the way they used their hindlimbs during movement. This asymmetry was most noticeable 48 hours after vaccination but had resolved by 96 hours.

 

A “push-off-type” asymmetry refers to changes occurring during the propulsion phase of movement. During locomotion, the hindlimbs generate the force needed to push the horse forward. If one hindlimb produces less force because of soreness or stiffness, the horse may shift more weight onto the opposite limb. This can create a subtle unevenness in gait that may resemble mild lameness.

 

The asymmetry observed in the study was described as measurable, meaning it could be detected using objective gait analysis techniques. Modern gait analysis often uses motion sensors or inertial measurement units attached to different parts of the horse’s body. These devices can identify very small changes in movement that may not always be visible to the human eye. Such technology is increasingly used in equine sports medicine to improve the accuracy of lameness detection.

 

The research team did not detect any clinically relevant changes in gait symmetry following vaccination into the pectoralis descendens or after saline (control) injection at either site.

 

Importantly, the effect observed after vaccination in the semitendinosus muscle was temporary and short-lived. The horses returned to normal symmetry within four days of vaccination, suggesting that the effect was likely related to temporary muscle soreness or mild local inflammation at the injection site rather than any serious injury. Mild inflammation is a normal immune response following vaccination, as the body reacts to the vaccine and begins developing immunity.

 

This finding is particularly relevant for veterinarians, owners, trainers, and equine therapists because temporary gait asymmetry following vaccination could potentially be mistaken for orthopaedic lameness or poor performance. Horses competing or undergoing lameness investigations shortly after vaccination may therefore show altered movement patterns unrelated to musculoskeletal disease.

 

The study also highlights the importance of appropriate vaccination scheduling. Since measurable asymmetry occurred around 48 hours after injection, strenuous exercise or competition immediately after vaccination may not be ideal. Many veterinarians already recommend a short period of lighter work following vaccination to allow horses time to recover from any mild soreness or systemic effects.

 

Overall, the study suggests that intramuscular vaccination into the semitendinosus muscle may cause short-term hindlimb asymmetry, but the effect appears mild, temporary, and self-resolving in healthy horses.

 

For more details, see:

 

J. Lenarz, I.H. Smit, M. Rhodin, C. Lischer, M.C. Fugazzola,

Vaccination-associated lameness in warmblood horses after intramuscular injection,

Journal of Equine Veterinary Science (2026), Vol 159,105820.

 

https://doi.org/10.1016/j.jevs.2026.105820

Ixodes ricinus: The importance of tick-borne disease in the UK and Europe

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The tick Ixodes ricinus, commonly known as the sheep tick, deer tick, or castor bean tick, is the
most widespread tick species in the United Kingdom and across much of Europe. It is medically and veterinary important because it can transmit a wide range of disease-causing microorganisms, known as tick-borne pathogens (TBPs), to humans, horses, livestock, wildlife, and pets. 

 

In the UK, I. ricinus is found mainly in areas with moist vegetation, rough grazing, heathland, woodland, and upland pasture. Large populations occur in southern England, Norfolk, the Scottish Highlands, Wales, the Lake District, and the North York Moors, although the species is spreading into new regions. The tick is considered a common and increasing problem in Britain, partly because warmer temperatures and milder winters linked to climate change improve tick survival.

 

Expanding deer populations, increased outdoor recreation, and greater contact between wildlife, horses, pets, and people also contribute to rising exposure. 

 

The most important disease carried by I. ricinus in the UK is Lyme disease, caused by bacteria from the Borrelia burgdorferi group. Lyme disease is the most common tick-borne infection affecting humans in Britain. Horses can also become infected, although clinical disease is less commonly recognised. Symptoms in horses may include lethargy, stiffness, lameness, muscle tenderness, behavioural changes, and poor performance.

 

The tick can also carry Anaplasma phagocytophilum, which causes equine granulocytic anaplasmosis. This disease may lead to fever, depression, limb swelling, jaundice, and reluctance to move. In addition, I. ricinus is capable of transmitting Babesia parasites, which infect red blood cells and can cause anaemia. Tick-borne encephalitis virus (TBEV), a virus affecting the nervous system, has also recently been identified in parts of the UK, although human cases remain rare. 

 

A recent Polish study led by Anna Rymaszewska investigated the occurrence of several TBPs in I. ricinus ticks collected from recreational forest areas, from ticks feeding on horses, and from red deer blood samples. The researchers used molecular diagnostic methods to identify the microorganisms present.

 

The study examined both “questing” ticks and feeding ticks. A questing tick is a tick actively searching for a host. Rather than jumping or flying, ticks climb vegetation and hold out their front legs in a behaviour called “questing.” When an animal or person brushes past, the tick attaches itself and begins feeding. 

 

The study found several pathogens in the ticks, including Borrelia afzelii, Borrelia garinii, Anaplasma phagocytophilum, and species of Rickettsia. B. afzelii and B. garinii are important causes of Lyme disease in Europe. B. afzelii is commonly associated with skin infections, while B. garinii is linked more closely with neurological disease. Rickettsia helvetica and related species may cause flu-like illness, fever, headache, and occasionally more serious disease in humans.

 

An important finding was the detection of multiple pathogens within single ticks or animals. Some ticks carried two, three, or even four pathogens simultaneously. This is significant because co-infections may increase disease severity, complicate diagnosis, and allow animals or humans to become infected with several diseases from one tick bite.

 

The study highlights the growing importance of tick surveillance and tick control in both veterinary and human medicine. Forest recreation areas, horse grazing land, and wildlife habitats can all act as hotspots for exposure. Understanding tick ecology and disease transmission is increasingly important for protecting horse health.

 

 

 

For more details, see:

 

Anna Rymaszewska, Katarzyna Kubiak, Małgorzata Dmitryjuk, Izabella Rząd, Lucyna Kirczuk.

Occurrence of tick-borne pathogens in questing ticks, ticks from riding horses, and red deer blood in Western Pomerania, Poland,

Veterinary Microbiology,(2026), Vol 315,110932,

 

https://doi.org/10.1016/j.vetmic.2026.110932

Feral horses shape their landscapes, study finds

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 Across Europe, many natural landscapes are undergoing rapid change. Warmer temperatures and increased
rainfall are accelerating the growth of shrubs and trees, gradually turning open habitats into dense woodland. While this process, known as ecological succession, is natural, it can threaten species that depend on light, open environments, such as wildflowers and insects. Traditionally, land managers have controlled this by cutting back vegetation. However, new research suggests that large grazing animals like horses and cattle may offer a more natural and effective solution.

This approach, known as trophic rewilding, involves introducing free-ranging herbivores into landscapes and allowing them to shape vegetation through their natural behaviour. A recent five-year study carried out in Denmark at the Mols Laboratory has provided valuable insight into how this works in practice. Researchers from Aarhus University tracked the movements of feral horses (Equus ferus caballus) and cattle (Bos taurus) across a 120-hectare rewilding site to understand how their grazing patterns influence vegetation.

Using GPS collars fitted to the animals and satellite data measuring vegetation growth (NDVI), the researchers were able to link where the animals spent their time with how the landscape changed over several years. The results showed that both horses and cattle preferred open grassland areas over dense woodland. In these frequently used areas, grazing and trampling reduced plant biomass and slowed the growth of shrubs and trees. As a result, these patches remained open for longer, supporting species that rely on sunlight and low vegetation.

However, the animals did not use the landscape evenly. Instead, they created a patchwork of heavily grazed and lightly grazed areas. This uneven grazing pattern is important because it increases habitat diversity, leading to a more varied and resilient ecosystem. Rather than maintaining a uniform landscape, the animals’ natural choices produced a dynamic mosaic of habitats.

Interestingly, the study also found that horses and cattle are not as similar as they are often assumed to be. While both species preferred similar grazing areas during times of abundance, their behaviour diverged when food became scarce. They began to use different parts of the landscape and exploit different food sources. This difference in “functional roles” is beneficial, as it enhances the overall impact on vegetation and promotes biodiversity more effectively than a single species would.

Another key finding was the influence of human-made structures. Both horses and cattle were strongly attracted to an artificial shelter within the study area, particularly the horses. This had a noticeable effect on grazing patterns, concentrating activity in specific areas. The researchers highlighted that the placement of infrastructure such as shelters or water troughs can unintentionally shape animal movement and, therefore, vegetation patterns. This is an important consideration for future rewilding projects.

The study also examined how the system responded to extreme weather, specifically the severe European drought of 2018. Areas that were heavily grazed showed the greatest decline in vegetation during the drought but also recovered the fastest afterwards. This ability to recover, known as resilience, suggests that grazing animals may help ecosystems better withstand climate extremes. However, when the herbivore population was later reduced by around two-thirds, the landscape became generally greener, indicating that the continued presence of grazing animals is essential to maintain open habitats.

Overall, the research demonstrates that year-round grazing by horses and cattle can effectively slow vegetation succession and prevent landscapes from becoming overly dense. For horse owners and equine science students, this highlights an important ecological role for horses beyond sport and recreation. When managed appropriately, horses can act as powerful agents of environmental change, contributing to biodiversity conservation and sustainable land management.

At the same time, the study emphasises that rewilding is not about leaving animals entirely  unmanaged. Animal welfare remains a priority, with populations carefully monitored to ensure that the land can support them. This balance between natural processes and responsible management is key to the success of rewilding initiatives.

In summary, horses and cattle do more than graze; they actively shape the landscapes they inhabit. By understanding their behaviour and ecological impact, we can use them to create healthier, more diverse environments in a changing world.

For more details,see:

Kristensen, Jeppe Å., Robert Buitenwerf, Emilio Berti, Oskar L. P.Hansen, Simon D.Schowanek, Rasmus Ejrnæs, Morten D. D.Hansen, Kent Olsen, Signe Normand, and Jens-Christian Svenning.

Space-Use by Feral Cattle and Horses Shapes Vegetation Structure in a Trophic Rewilding Area.”

Ecological Applications2026: 36(1): e70170

 https://doi.org/10.1002/eap.70170

 

Do horses grieve the loss of a companion?

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Horses are highly social animals that form close bonds with other members of their group.
Because of this, it is reasonable to expect that the loss of a companion may affect their behaviour and emotional wellbeing. 

However, until recently, there has been surprisingly little scientific research into how hoes respond to the death of another horse. A study led by Claire Ricci-Bonot and Daniel Mills at the University of Lincoln, with MSc student Emily Wilson, alongside Stefania Uccheddu of the San Marco Veterinary Clinic and Laboratory, Padua, Italy aimed to address this gap. 

The researchers used an online survey of horse carers in the UK, collecting data on 325 horses that had experienced the loss of a companion. Information was gathered on management, the relationship between the horses, and the behavioural responses of the surviving horse both immediately after the death and over the following months. 

The results showed that most horses displayed noticeable behavioural changes within 24 hours of losing a companion. These changes were often linked to increased arousal, such as restlessness or agitation, which was reported in nearly 89% of cases. Many horses also showed altered behaviour towards other horses and humans (around 77%), increased alertness to their surroundings (73%), and more frequent vocalisation (69%). In addition, over two-thirds of horses increased their movement, while more than half reduced their feeding time and contact-seeking behaviour with humans. 

These responses suggest that horses may experience something like grief-related behaviours. In Equus ferus caballus, such changes could reflect stress, confusion, or the disruption of a social bond. Importantly, the type of relationship between the two horses influenced the severity of the response. Horses that had formed close or affectionate bonds, rather than simply coexisting, were more likely to show stronger behavioural changes. For example, they were more likely to alter their enthusiasm for social interaction or feeding, and their behaviour towards humans. 

Another key finding was the impact of witnessing the death. Horses that had seen their companion die were more likely to show immediate changes in feeding and sleeping behaviour, as well as increased vigilance and altered social responses. This suggests that awareness of the death event itself may influence how horses process the loss. Interestingly, whether the surviving horse was allowed to spend time with the body did not appear to affect behaviour in the first 24 hours. 

However, over the longer term (up to six months), differences became clear. Horses that were given the opportunity to investigate or remain with the body were less likely to show ongoing changes in vocalisation and social behaviour. In contrast, those that were not allowed this contact were more likely to remain in a heightened state of arousal and vigilance. 

This finding has important implications for horse management and welfare. Although many behavioural changes began to decrease over time, some persisted for up to six months, indicating that the effects of losing a companion can be long-lasting. The degree of impact varied between individuals, suggesting that factors such as personality, environment, and previous experiences may also play a role. 

Overall, this study provides evidence that horses may exhibit behaviours consistent with grief, although further research is needed to fully understand the emotional processes involved. These findings highlight the importance of considering the social and emotional needs of horses, particularly during times of loss. Allowing horses appropriate time and space to adjust, and recognising signs of stress or behavioural change, can help support their welfare during what may be a challenging period 

 For more details, see: 

Claire Ricci-Bonot, Emily Wilson, Stefania Uccheddu, Daniel Simon Mills, 

Grief-like distress responses in horses after the death of a conspecific. 

Applied Animal Behaviour Science (2025) Vol 292,106799, 

https://doi.org/10.1016/j.applanim.2025.106799

New use for hoof trimmings?

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Horse owners are very familiar with hoof trimmings: they are a routine by-product of farriery visits and are usually
swept up and discarded without much thought,  if not eaten by the dog first. However, recent scientific research suggests that these small clippings may have much greater value than previously realised. A growing body of work in materials chemistry and biopolymer engineering is exploring how horse hoof trimmings could become a sustainable and useful natural resource.

 

At the centre of this research is keratin, a tough structural protein that gives strength and resilience to materials such as hair, wool, feathers, and hooves. Keratin is well known for its excellent mechanical properties (it is strong and durable) and biochemical stability (it resists breakdown). Because of these qualities, keratin has potential uses in a wide range of applications, from biodegradable plastics to medical materials.

 

Currently, most keratin-rich waste, such as poultry feathers, sheep wool, and animal hooves, is either burned (incinerated) or sent to landfill. This creates environmental problems, including greenhouse gas emissions and the loss of potentially valuable biological resources. In contrast, horse hoof trimmings represent an underused and more sustainable alternative.

 

One of the key advantages of hoof trimmings is that they are produced regularly as part of routine horse care. Every time a farrier trims a horse’s hooves, keratin-rich material is removed to maintain hoof health and balance. This means hoof trimmings are a renewable resource that does not require additional harvesting or harm to the animal. Unlike keratin sources obtained from slaughtered animals, hoof trimmings are also considered cruelty-free, which may be important for ethical and consumer reasons.

 

From a scientific perspective, hoof keratin is a high-quality material. Studies have shown that its chemical composition and structure are similar to other keratin sources, but with some unique features. The properties of hoof keratin can vary depending on factors such as the horse’s nutrition, living environment, and management practices. For example, diet influences the availability of amino acids needed for keratin production, while environmental conditions such as moisture can affect hoof quality. This means that hoof trimmings could even provide indirect information about horse health and management.

 

Researchers are now investigating how to extract keratin from hoof trimmings using more environmentally friendly (“green”) methods. Traditional extraction techniques often involve harsh chemicals or high energy use, which reduces sustainability. Newer approaches aim to minimise environmental impact while still producing high-quality keratin. These include using mild chemical treatments, enzymes, or recyclable solvents.

 

Once extracted, keratin can be upcycled, that is, transformed into higher-value products. Potential applications include:

• Biodegradable packaging materials
• Fertilisers or soil conditioners
• Medical products such as wound dressings
• Fibres for textiles or composites 

These innovations are closely linked to the idea of circular economy, where waste materials are reused and repurposed instead of discarded. By turning hoof trimmings into useful products, researchers hope to reduce waste and make better use of natural resources.

 

However, there are still challenges to overcome. Collecting and processing hoof trimmings on a large scale may be difficult, as they are currently dispersed across many small yards and farriers. In addition, more research is needed to optimise extraction methods and ensure that keratin-based products are safe, cost-effective, and competitive with existing materials.

 

In summary, horse hoof trimmings are no longer just waste, they are an emerging example of how everyday equine practices can connect to wider issues such as sustainability, innovation, and environmental responsibility.

 

For more details, see:

 

Esther Trigueros, Sara Mattiello, Lisa Rita Magnaghi, Carlo Santulli, Raffaela Biesuz,

Horse Hoof Trimmings as an Untapped Resource for Sustainable Keratin Utilization

ChemistryOpen2026, 15, e202500575.

 https://doi.org/10.1002/open.202500575

Evidence for Iron Age horse use from skeletal pathology and dental wear

Photographs of the preserved upper (premolar (p 2–4) 

and molar (m 1–2) teeth) and lower premolar tooth 

showing wear patterns. Red arrows indicate 

areas of extensive tooth wear. © Karastoyanova et al 2026

      The study of ancient horse remains provides valuable insight into how humans first used and managed horses.

Archaeological discoveries, particularly well-preserved skeletons, can reveal signs of riding, traction, or other forms of domestication.

 

Researchers in Bulgaria, led by Nadezhda Karastoyanova, examined an ancient horse skeleton recovered during excavations at an early settlement site in Chirpan, located in the Thracian Valley. The site contained numerous animal remains found in close association with human activity, suggesting an integrated human-animal environment. The full findings of this study have been published in the International Journal of Paleopathology.

 

Radiocarbon dating places the skeleton in the Early Iron Age, about the 8th century BCE. This makes it one of the few well-documented equine skeletons from this period in Bulgaria, providing valuable insight into early horse use in the region. The relatively complete condition of the specimen allowed researchers to carry out a detailed examination of both the skull and axial skeleton. Such a high level of preservation is essential for identifying subtle indicators of human-horse interaction, including evidence of management, workload, and possible domestication practices.

One of the most significant findings was unusual wear on the horse’s teeth. Patterns of wear on the premolars were consistent with what is often described as “bit wear,” caused by repeated contact with a bridle and bit placed in the horse’s mouth. This type of wear typically appears as smoothing or bevelling on the anterior edges of the teeth and is widely regarded as evidence of human control, particularly in ridden or driven horses.

 

The presence of dental wear suggests that this horse may have been accustomed to carrying a rider or being directed through reins. While alternative explanations such as natural abrasion must always be considered, the pattern and location of the wear strongly support the interpretation of deliberate bit use. This provides important evidence for early horsemanship practices.

Examination of the vertebral column revealed several notable pathological changes. These included periosteal bone proliferation, spondylopathic alterations, and partial fusion between adjacent vertebrae. Together, these features indicate a chronic condition rather than an acute injury.

 

Periosteal bone proliferation reflects the body’s response to repeated stress, leading to new bone formation along the vertebrae. Spondylopathic changes suggest degeneration of the spinal joints, often associated with long-term mechanical loading. Partial vertebral fusion represents a more advanced stage, where the spine becomes less flexible due to the joining of vertebrae.

 

These changes are consistent with prolonged biomechanical strain acting on the horse’s back. Rather than resulting from a single traumatic event, the lesions point to repeated loading over an extended period. In modern contexts, similar patterns are often associated with ridden horses, pack animals, or those used for draught work.

When considered together, the dental and skeletal evidence provides a compelling picture of how this horse may have been used. The presence of bit wear suggests active human control, while the spinal changes indicate sustained physical demands placed on the animal.

 

It is therefore plausible that this horse was used for riding, carrying loads, or possibly pulling light vehicles or equipment. The chronic nature of the vertebral lesions implies that such activities were performed regularly over the animal’s lifetime. This supports the idea that horses were not only domesticated but also integrated into daily human activities requiring endurance and strength.

 

The combination of dental wear and vertebral pathology in this ancient horse skeleton offers valuable evidence for early human–horse relationships. Bit-related dental wear indicates controlled handling, while spinal lesions reveal the physical impact of sustained work. Together, these findings contribute to our understanding of how horses were used in the past, highlighting their important role in transport, labour, and possibly riding. Such studies continue to deepen our knowledge of domestication and the long-standing partnership between humans and horses.

 

 

For more details, see:

 

Nadezhda Karastoyanova, Petar Stamberov, Stella Nikolova, Petar Leshtakov,

Early Iron Age horse exploitation in Thrace (Bulgaria) inferred from dental attrition and vertebral pathology,

International Journal of Paleopathology,(2026) Vol 52, Pp 119-127,

 

https://doi.org/10.1016/j.ijpp.2026.01.007

Using simple ECG screening to identify racehorses at risk of exercise-induced arrhythmias

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A simple heart test carried out during a horse’s warm-up may help identify racehorses at risk of
developing dangerous heart rhythm problems during exercise. This new research, led by the University of Surrey, highlights how short electrocardiogram (ECG) recordings could be used as a practical screening tool in everyday training.

 

Cardiac arrhythmias (abnormal heart rhythms) are very common in athletic horses. In many cases they are harmless, but some can reduce performance or, in rare cases, lead to collapse or sudden death during exercise. One of the biggest challenges for veterinarians is identifying which horses are at risk before serious problems occur.

 

Traditionally, detecting these issues requires ECG monitoring during high-intensity exercise. However, this can be time-consuming, expensive, and not always practical. The new study suggests that useful information can instead be obtained from short ECG recordings taken at rest or during light exercise, such as a warm-up trot.

 

The research team analysed ECG data from 110 Thoroughbred and Standardbred racehorses in the United States during routine training. These recordings were collected using portable (ambulatory) ECG devices, allowing horses to be monitored while moving freely. From these data, the researchers selected 60-second segments where the signal quality was good and the heart rate was stable, typically between 60 and 100 beats per minute.

 

Rather than simply looking for obvious irregular beats, the researchers used advanced mathematical techniques to assess the “disorderliness” of the ECG signal. This is known as non-linear analysis and includes methods such as entropy and complexity measurements (for example, Lempel–Ziv complexity and Shannon entropy). These techniques examine how predictable or irregular the heart’s electrical activity is, even when the rhythm appears normal (sinus rhythm).

 

The idea behind this approach is that subtle changes in the ECG signal may indicate an underlying tendency to develop arrhythmias later, especially during intense exercise. In other words, the heart may show early warning signs before any abnormal beats are visible.

 

To test this, the team applied six different algorithms to the ECG data and compared their ability to distinguish between horses that did and did not develop arrhythmias during exercise. The best-performing method achieved an “area under the curve” (AUC) of 0.86. For context, an AUC of 0.5 indicates no better than chance, while 1.0 represents perfect accuracy. Therefore, a value of 0.86 suggests good diagnostic performance.

 

An important finding was that the test was particularly effective at ruling out horses that are unlikely to be at risk. This means it could be used as a first-line screening tool: horses with a negative result could continue normal training, while those that test positive could be referred for more detailed testing, such as a full exercising ECG.

 

This approach builds on earlier work showing that similar ECG analysis methods can detect atrial fibrillation, another common arrhythmia in horses. Because these methods work at different heart rate ranges, it may be possible in the future to screen for multiple heart conditions during a single, low-intensity session.

 

Overall, this study demonstrates that short, simple ECG recordings—combined with advanced data analysis—could help identify at-risk horses earlier. This has important implications for improving both performance monitoring and the safety and welfare of racehorses.

 

 

For more details, see:

 

Vadim Alexeenko, Hamid Tavanaeimanesh, Freya Stein, Jenifer Gold, Lauren Hughes, Molly McCue, Celia Marr, Sian Durward-Akhurst & Kamalan Jeevaratnam 

Detection of exercising ectopic atrial and ventricular beats using non-linear analysis of clinically normal racehorse electrocardiograms at rest or low-intensity exercise. 

Sci Rep (2026). 

https://doi.org/10.1038/s41598-026-41281-0