Seasonal and breed differences in resting ACTH

Pituitary pars intermedia dysfunction (PPID), commonly referred to as equine Cushing’s
disease, is a common endocrine disorder primarily affecting older equids. Current estimates suggest that approximately 25% of horses and ponies aged 15 years and older may be affected.

The condition arises from degeneration of dopaminergic neurons within the hypothalamus, leading to loss of regulatory control over the pars intermedia region of the pituitary gland. As a result, excessive production of several hormones, including adrenocorticotropic hormone (ACTH), occurs. Although PPID is progressive and currently incurable, early diagnosis and appropriate management can significantly slow disease progression and improve equine welfare.

Clinical signs of PPID are variable and may develop gradually. Common indicators include hypertrichosis (abnormal or excessive hair growth), delayed or incomplete shedding of the winter coat, lethargy, weight loss, and metabolic disturbances. One of the most serious associated complications is laminitis, which can severely compromise quality of life and may become life-threatening. Due to the variable presentation of clinical signs, diagnostic testing is frequently required to support clinical suspicion.

Measurement of baseline plasma ACTH concentration is widely used as a primary diagnostic tool for PPID. However, interpretation of ACTH values is complex, as concentrations are influenced by several factors, particularly seasonal variation. In the Northern Hemisphere, resting ACTH levels typically rise during late summer and early autumn, approximately between August and October. Understanding these physiological fluctuations is essential to avoid misinterpretation of results and potential overdiagnosis.

Breed-related differences in ACTH concentrations have also been documented. An Australian study identified that pony breeds, particularly Shetland ponies, displayed significantly higher ACTH concentrations during autumn when compared with Thoroughbred horses. These findings suggest that species, breed type, and possibly body size may influence endocrine responses and should be considered during diagnostic evaluation.

Further research has expanded understanding of ACTH variation across different equid species. A study conducted by Goodrich and colleagues, involving researchers from Cornell University, the University of California, Davis, and private veterinary practice, investigated baseline ACTH concentrations in donkeys and horse–donkey hybrids across several regions of the United States. The study aimed to provide a more comprehensive understanding of seasonal ACTH variation in healthy equids, as previous research had been limited by small sample sizes and restricted geographic representation.

The study evaluated 19 standard donkeys, 14 miniature donkeys, and 28 hybrids, with animals located in California, Massachusetts, New York, and Texas. Blood samples were collected twice monthly from June to November 2019 and monthly from December 2019 to May 2020. Results demonstrated a clear seasonal rise in ACTH concentrations across all groups, with levels increasing from mid-August and peaking in late September. Mean ACTH concentrations during peak periods reached approximately 109.6 pg/mL in standard donkeys, 134.6 pg/mL in miniature donkeys, and 100.8 pg/mL in hybrids.

Notably, hybrids consistently exhibited lower ACTH concentrations compared to donkeys throughout the year. During the seasonal peak, ACTH levels in hybrids were 23% lower than in standard donkeys and 51% lower than in miniature donkeys. Similar differences persisted during non-peak periods, with hybrids showing reductions of approximately 30% compared to both donkey groups. These findings highlight important species-related differences that may influence diagnostic interpretation.

Overall, research demonstrates that accurate diagnosis of PPID requires careful consideration of seasonal variation, species differences, and breed predisposition alongside clinical assessment. Improved understanding of normal ACTH fluctuations in healthy equids enhances diagnostic accuracy and supports more effective management of this common and welfare-significant endocrine disorder.

 

For more details, see:

Goodrich, Erin L., Sebastián Gonzalo Llanos-Soto, Renata Ivanek, Toby Pinn-Woodcock, Elisha Frye, Amy Wells, Stephen R. Purdy, Emily Berryhill, and Ned J. Place.

Both Season and Equid Type Affect Endogenous Adrenocorticotropic Hormone Concentrations in Healthy Donkeys, Mules and Hinnies in the United States

 Animals (2026) 16, no. 2: 290.

https://doi.org/10.3390/ani160202902

AI-based system for real-time detection of whip sounds in horse racing

© Aaron Johnson Dreamstime.com

  

Researchers at the University of Tsukuba have developed an artificial intelligence–based system capable of
automatically detecting whip sounds in horse racing, offering a potential alternative to the labour-intensive manual review processes currently used to enforce whip regulations.

In many racing jurisdictions, the use of whips is strictly regulated to protect animal welfare and ensure fair competition. Violations, such as excessive force or exceeding the allowed number of strikes, are typically identified by race stewards through careful frame-by-frame analysis of video footage. While effective, this approach is time-consuming, costly, and impractical for real-time enforcement during live races. The new study addresses these limitations by focusing on the acoustic signature of whip strikes rather than visual evidence.

Whip sounds are highly impulsive and contain very high-frequency components that are difficult to capture using conventional audio recording systems. To overcome this challenge, the research team recorded race audio at an unusually high sampling rate of 192 kHz, enabling precise capture of both the high-frequency content and the fine temporal structure of whip strikes. Audio data were collected from 24 official horse races held in Japan, yielding a dataset that included 620 carefully annotated whip strike events.

Using this dataset, the researchers built an automated system to detect whip sounds in race audio. The system was trained to recognise the acoustic patterns of whip strikes and how these sounds change over time. Several model designs were tested to find the most effective way to detect the very short, high-pitched nature of whip sounds.

One major challenge was that whip strikes occurred far less often than background noise such as crowd sounds and hoofbeats. To prevent the system from being biased toward this background noise, the researchers reduced the amount of non-whip audio used during training. The best-performing model correctly identified whip strikes with an accuracy score of 69.8%.

Beyond accuracy, the study also examined processing speed. Offline evaluations revealed that the best-performing model could analyse audio faster than real time under many conditions, suggesting that live race monitoring is technically feasible. 

The research provides the first clear confirmation that whip sounds contain critical very high-frequency elements, underscoring the importance of high-sampling-rate audio for this application. At the same time, the authors acknowledge remaining challenges, including environmental noise in race settings and the relatively small size of the current dataset, which can affect robustness and generalization.

Overall, the study establishes an approach for automatic whip strike detection using sound event detection and deep learning. With further data collection and improvements in noise robustness, the system could support real-time rule enforcement, promote fairer competition, and contribute to improved animal welfare in horse racing.

 

For more details, see:

Aoi Taguchi, Yuki Fujita, Keiichi Zempo,

Whip strike detection using high-sampling-rate audio by evaluating convolutional recurrent neural network configurations and class imbalance strategies,

Engineering Applications of Artificial Intelligence (2026) Vol 164, Part A,113272,

ISSN 0952-1976,

https://doi.org/10.1016/j.engappai.2025.113272

Equine Grass Sickness Fund 2026 Conference

This year the Equine Grass Sickness Fund (EGSF) Conference will take place at the Moredun Research Institute, Edinburgh on 25th March.

Equine Grass Sickness is a devastating disease of the equine nervous system, with an 80% fatality rate, and remains a significant cause of equine mortality in the UK and worldwide. The EGSF is the only UK charity dedicated solely to funding research into this disease.

The conference will bring together a range of speakers, including leading scientists, vets, and equine health experts, to share the latest research and insights throughout the day.

Can’t attend in person? The conference will be recorded, with online tickets available. A viewing link will be sent to all ticket holders nearer the event, and access to the recording will be available after the conference.

For more details, see:

https://www.grasssickness.org.uk/equine-grass-sickness-fund-conference/

Drones reveal how feral horse units quietly police their boundaries

Feral horses studied in this research 

 (c) Tamao Maeda

Feral horses are often admired for their apparent freedom, yet life in a wild herd involves constant negotiation. New research using drone technology has now revealed just how precisely horses manage space and social boundaries when living alongside neighbouring groups. It turns out they are far more flexible and strategic than previously understood.

Unlike territorial species that defend fixed areas, feral horses in northern Portugal live in a multilevel society. The basic social unit is a family group, typically led by a stallion with several mares and their offspring. Multiple units aggregate into larger groups, gaining protection from predators and harassment by bachelor males. However, this close proximity also brings rival stallions into frequent contact, creating the risk of costly aggression.

To understand how horses manage this trade-off, a research team led by Kyoto University observed 25 reproductive units in Serra d’Arga, Portugal. Using drones, they conducted 166  detailed aerial observations and applied statistical and spatial analyses to quantify how unit shapes and positions changed as other units approached.

The results show that spacing between units is anything but accidental. When compared with randomised models, real horse units were significantly less likely to be close to neighbouring units than expected by chance. Even when proximity increased, mixing was actively avoided, confirming that horses deliberately manage their spatial relationships to maintain social order.

Crucially, the study found that horses adjust not only where they stand, but how their group is shaped. As neighbouring units came closer, a unit would become more circular and cohesive. This likely reduces the number of individuals exposed along the edge, minimising the risk of accidental boundary crossings or confrontations. When another unit approached extremely closely, the formation changed again: the group elongated, effectively reshaping itself so that unit boundaries did not overlap.

These subtle but consistent adjustments suggest that horses maintain flexible, invisible boundaries rather than rigid territorial lines. By reshaping their group structure in response to their neighbours, they balance the benefits of aggregation with the need to avoid conflict; a sophisticated solution in a fluid social environment.

There was, however, one remarkable exception. Two units, led by stallions named Kobe and Uzumasa, repeatedly broke the rules. Unlike all other pairs, these units frequently crossed boundaries and intermixed, doing so in 21 out of 59 observations. This behaviour was not a one-off anomaly: similar interactions had been recorded as far back as 2016. No other units in this population, or in comparable studies elsewhere, have shown such high levels of mutual tolerance.

This “friendly pair” appears to represent a previously unrecognised social layer within horse multilevel societies, suggesting that long-term, unit-to-unit relationships can exist under certain conditions. Why these two stallions tolerate such close association remains unknown, but it opens new questions about alliance formation, kinship, or individual temperament in horses.

The findings offer a valuable reminder: horses are highly sensitive to space, proximity, and social context. Even in domestic settings, subtle changes in grouping, density, or layout may influence stress and behaviour more than we realise.

Overall, the study highlights that feral horses maintain harmony not through force or fixed borders, but through constant, adaptive spatial negotiation.

 

For more details, see: 

 

Spatial strategies in non-territorial societies: how feral horses maintain boundaries with other groups

Tamao Maeda; Sota Inoue; Monamie Ringhofer; Satoshi Hirata; Shinya Yamamoto  

Proc Biol Sci (2026) 293 (2063): 20252468 .

https://doi.org/10.1098/rspb.2025.2468

Horses can smell fear

(c) Jardat et al. PLoS one. CC-BY 4.0

 Researchers led by Plotine Jardat, working with colleagues from the Institut Français du Cheval et de l’Équitation and several French research institutions, conducted a study to explore whether horses can detect and respond to emotional information carried in human body odours. The work focused on olfactory communication, a sensory channel that is widespread in animals but still poorly understood in the context of human–animal interactions.

Olfaction plays a central role in communication for many species, particularly in social and emotional contexts. While previous research has mainly examined olfactory signals within the same species, emerging evidence suggests that chemosignals may also operate between species. This study investigated whether human emotional states, specifically fear and joy, can be perceived by horses through smell, and whether these odours influence equine behaviour and physiology.

The experiment involved 43 adult Welsh mares housed at the Animal Physiology Experimental Unit of l’Orfrasière (UEPAO) in Nouzilly, France. Human odours were collected from volunteers using cotton pads placed in the armpits. Volunteers wore the pads while watching 20 minutes of either fear-inducing (horror) or joy-inducing film clips. To minimise confounding factors, participants followed strict hygiene routines and dietary restrictions for two days prior to odour collection. Unused cotton pads served as a control condition.

During testing, each horse was fitted with a disposable lycra muzzle positioned over the nostrils. Attached to the muzzle were either two unused cotton pads (control group) or two pads from a single volunteer collected in either a fear or joy context. Horses were exposed to only one odour condition.

The experimental protocol consisted of both human–horse interaction tests and fear-related tests. In the morning, horses completed a grooming test and a free human approach test, designed to assess their willingness to interact with a person. In the afternoon, they underwent a suddenness test, involving an unexpected stimulus, and a novel object test, which assessed reactions to an unfamiliar item. Alongside behavioural observations, physiological measures were collected, including heart rate and salivary cortisol levels, to evaluate stress and emotional arousal.

The results showed clear differences between odour conditions. Horses exposed to fear-related human odours interacted less with the experimenter during the human approach test and displayed stronger fear-related behaviours than horses exposed to joy-related or control odours. Specifically, horses in the fear condition touched the human significantly less and spent more time gazing at the novel object, indicating heightened vigilance. They were also more strongly startled by sudden stimuli.

Physiological data supported the behavioural findings. Horses in the fear group showed significantly higher maximum heart rates compared with those in the joy and control groups, suggesting increased emotional arousal. Post-hoc analyses confirmed these differences, and principal component analysis revealed an overall pattern of heightened fear responses and reduced human interaction when horses were exposed to fear-related odours.

The authors concluded that human emotional body odours can influence both behaviour and physiology in horses. Sweat samples collected during fearful situations induced greater fear responses and reduced willingness to engage with humans, whereas joy-related odours did not produce these effects. These findings highlight the importance of chemosignals in interspecific emotional communication and raise interesting questions about how domestication may have shaped horses’ sensitivity to human emotional cues.

From a practical perspective, the study suggests that a handler’s emotional state may influence horses not only through body language and voice, but also through smell. For horse owners, trainers, and equine professionals, this research underlines the potential value of remaining calm and emotionally regulated during interactions, as emotional signals may be transmitted in ways that are subtle yet biologically meaningful to horses.

For more details, see:  

Jardat P, Destrez A, Damon F, Tanguy-Guillo N, Lainé A-L, Parias C, Reigner F, Ferreira VHB, Calandreau L, Lansade L.

Human emotional odours influence horses’ behaviour and physiology. 

PLoS One (2026) 21(1): e0337948. 

https://doi.org/10.1371/journal.pone.0337948

Stress biomarkers and stereotypic behaviour in Thoroughbred horses

(c) Dahlskoge Dreamstime.com

 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

(c) Virgonira Dreamstime.com

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