Exercise, the gut microbiome and health

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 The gut microbiome - the diverse community of bacteria, fungi, viruses and other microorganisms that inhabit the gastrointestinal tract - has become a major focus of research in both human and veterinary medicine.

 

Far from being passive inhabitants, these microorganisms play a crucial role in host health, influencing digestion, metabolism, immune function and even neurological processes. Growing evidence suggests that the composition and diversity of the gut microbiome can affect susceptibility to a wide range of conditions, including obesity, cardiovascular disease, autoimmune disorders and inflammatory diseases.

 

In human medicine, among the many factors that influence the microbiome, regular physical activity has emerged as one of the most important. Exercise is widely recognised for its benefits to digestive and systemic health, and research indicates that many of these effects may be mediated through changes in the gut microbiota. Regular moderate-to-vigorous exercise has been shown to increase microbial diversity, a characteristic strongly associated with better physical and mental health.

 

In contrast, reduced microbial diversity has been observed in individuals with obesity, cardiometabolic disease and certain autoimmune conditions.

 

While these effects are increasingly well documented in humans, less is known about the relationship between exercise and the gut microbiome in horses. A recent study, published in  Microbial pathogenesis, investigated this question by examining the effects of exercise on equine gut bacterial and fungal communities using 16S rDNA and ITS gene amplicon sequencing.

 

The results demonstrated that exercise significantly increased bacterial diversity, as reflected by higher ACE, Chao1 and Shannon diversity indices - commonly used measures of microbial diversity in ecological and microbiome studies. The increases in ACE and Chao1 suggest that exercise was associated with a greater number of bacterial taxa in the gut, while an increase in the Shannon index indicated that the bacterial community became both richer and more evenly distributed. Together, these findings suggest that exercise promoted a more diverse gut bacterial ecosystem.

 

Exercise also altered the overall composition of the bacterial community. Specifically, the relative abundance of eight bacterial phyla and 187 bacterial genera increased, while three phyla and 197 genera decreased significantly.

 

In contrast, exercise had little effect on the overall diversity and abundance of the fungal community, although significant changes were observed in the abundance of specific fungal taxa. Exercise increased the relative abundance of five fungal phyla and 105 genera, while reducing two phyla and 82 genera.

 

These findings indicate that exercise can substantially modify the composition and structure of the equine gut microbiota, particularly the bacterial component. The study supports the growing concept that exercise may promote health by shaping the gut microbial ecosystem.

 

Future research examining different exercise types and intensities may further clarify how physical activity can be used to optimise microbiome health and improve management strategies in both humans and horses.

 

For more details, see:

 

Ma, Rufei., & Wang, Chong.

Microbiome analysis reveals the positive effects of exercise on the gut microbiota in horse. 

Microbial pathogenesis (2026) , 216, 108501.

https://doi.org/10.1016/j.micpath.2026.108501

 

Could ertugliflozin reduce laminitis risk following corticosteroid joint injections?

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Intra-articular (IA) corticosteroid injections are widely used in equine practice to manage joint
pain and inflammation associated with conditions such as osteoarthritis. One commonly used corticosteroid is triamcinolone acetonide (TA), which can provide significant relief from lameness and improve performance. However, growing evidence suggests that even when corticosteroids are administered directly into a joint, they can have effects throughout the body, including alterations in blood glucose and insulin concentrations.

This is important because elevated insulin concentrations (hyperinsulinaemia) are strongly associated with endocrinopathic laminitis, one of the most common and serious causes of laminitis in horses. Horses with Equine Metabolic Syndrome (EMS) or insulin dysregulation (ID) are considered particularly vulnerable, but any horse experiencing a substantial increase in insulin may be at risk.

Researchers have recently investigated whether ertugliflozin, a member of the sodium-glucose co-transporter 2 inhibitor (SGLT2i) drug class, could help reduce these post-corticosteroid insulin increases. In human medicine, SGLT2 inhibitors are commonly used to treat Type 2 diabetes by promoting the excretion of glucose through the urine, thereby reducing blood glucose and insulin levels. More recently, these drugs have attracted attention in equine medicine as a treatment for severe insulin dysregulation.

Two independent studies have now examined the effects of ertugliflozin administration around the time of IA corticosteroid treatment in horses.

The first study, conducted by Page and colleagues at the University of Kentucky, used eight metabolically normal geldings in a controlled crossover design. Horses either received no treatment or were given ertugliflozin for seven days before and seven days after receiving a clinically relevant dose of triamcinolone acetonide. Researchers measured resting glucose and insulin concentrations and performed oral sugar tests to assess the horses' insulin responses.

The results showed that horses receiving ertugliflozin had significantly lower blood glucose and insulin concentrations following corticosteroid administration. Resting glucose concentrations remained lower for up to 48 hours after injection, while resting insulin concentrations were lower for up to 72 hours. Insulin responses during oral sugar testing were also reduced. Importantly, no obvious adverse effects were observed during the study.

A second study by Darch and colleagues produced similar findings. Using a randomised, blinded, placebo-controlled crossover design, eight Standardbred geldings received either ertugliflozin or a placebo before and after IA triamcinolone administration. The researchers monitored blood insulin, glucose and triglyceride concentrations over the treatment period.

Again, ertugliflozin substantially reduced the insulin response following corticosteroid injection. The peak insulin concentration (Cmax) was approximately 40 μIU/mL in the placebo group but only 17 μIU/mL in horses receiving ertugliflozin. Statistical analysis indicated a greater than 99% probability that the peak insulin concentration was lower when horses received ertugliflozin.

Together, these studies provide encouraging evidence that ertugliflozin can attenuate the increases in blood glucose and insulin that occur following IA corticosteroid administration. This finding is particularly relevant because corticosteroid-associated hyperinsulinaemia may contribute to laminitis risk.

However, both studies were conducted in horses that did not have insulin dysregulation. Consequently, the most important question remains unanswered: can ertugliflozin reduce post-corticosteroid insulin elevations in horses already suffering from EMS or ID, where the risk of laminitis is greatest?

Further research is now needed to determine whether this treatment strategy can safely protect high-risk horses. If successful, ertugliflozin could become an important tool that allows veterinarians to continue using corticosteroid joint injections while reducing the metabolic complications that may accompany them.

 

For more details,see:

1) Allen E Page,  Jenna L McPeek,  Ella McGreevy,  Sophia Carattini,  Emma N Adam.  

Treatment with ertugliflozin mitigates the hyperinsulinemic response to intra-articular triamcinolone acetonide. 

Equine Vet J.  2026.

https://doi.org/10.1002/evj.70150

 

2) Cara Darch, Timothy H. Hyndman, David Byrne, David Ian Rendle, Barny Fraser,

Ertugliflozin decreases the insulin spike in non-insulin dysregulated standardbred horses following intra-articular triamcinolone administration,

Domestic Animal Endocrinology, (2026) Vol 96,107016,

https://doi.org/10.1016/j.domaniend.2026.107016

Free webinar supports call for posters for Horses Inside Out Conference 2027

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A call has been made for scientific posters centred on the theme of wellness and welfare for the
2027 Horses Inside Out Conference. Equine coaches, therapists, and industry professionals are being encouraged to contribute research, case studies, and practical observations as part of the conference programme.

The initiative provides an opportunity for professionals within the equine sector to present their expertise in a scientific format and contribute to ongoing discussions surrounding equine wellness and welfare. Contributors are invited to transform their practical experience and case studies into engaging scientific posters that may help advance understanding within the field.

To support participants through the process, Professor Meriel Moore-Colyer will host a free webinar entitled “Mastering Scientific Posters” on Monday 1st June. The webinar is designed to guide attendees through each stage of poster creation, including selecting an appropriate topic, developing ideas, and designing an effective and visually compelling scientific poster.

The webinar aims to make the process accessible and supportive for those who may feel unfamiliar with scientific poster presentation, while encouraging wider participation in equine science and welfare discussions.

For more details, see: 

https://www.horsesinsideout.com/webinars

 

Effects of a fibre-based forage feed on hindgut fermentation and microbiome

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As understanding of equine gut health continues to evolve, increasing attention is being focused on the relationship between diet and the horse’s hindgut microbiome. The microbial community structure (MCS) within the hindgut plays a critical role in fibre digestion, nutrient utilisation, immune support, and overall gastrointestinal health. Although numerous commercial feeds and supplements are marketed to support digestive function and optimise nutrition, relatively little research has examined how these products influence the equine hindgut microbiome.

 

Newly published research conducted by K.J. Hart, M.J. Hegarty, E.H. Hart at Aberystwyth University sought to address this knowledge gap by investigating the effects of a complementary fibre-based forage feed* on hindgut fermentation and microbial community structure under controlled laboratory conditions.

 

The study aimed to evaluate how the feed influenced fermentation profiles and microbial populations when added to two contrasting basal diets: a forage-only diet (FOR) and a mixed forage-and-concentrate diet (MIX). Researchers used an in vitro hindgut fermentation model designed to simulate conditions within the equine large intestine.

 

While in vitro systems cannot replicate every aspect of the living horse, they provide valuable tools for studying microbial activity under carefully controlled conditions. These laboratory models allow researchers to isolate dietary effects without the many variables present in live-animal trials. However, the authors acknowledged that such systems cannot fully reproduce the complexity of the equine gastrointestinal tract, including immune responses, intestinal motility, hydration dynamics, stress, exercise, and long-term microbial adaptation.

 

Using a 2 × 2 factorial design, the researchers examined fermentation characteristics and microbial community changes in vessels receiving either the forage-only or mixed diet, with or without inclusion of the fibre-based feed. Each treatment was replicated three times. Artificial saliva was continuously infused into the fermenters, and feed bags were incubated for 24 and 48 hours to assess microbial community structure.

 

The study demonstrated clear differences between the two basal diets. The MIX diet produced a lower hindgut pH and higher total volatile fatty acid production compared to the forage-only diet, indicating altered fermentation activity. These findings reinforce existing knowledge that concentrate inclusion can significantly influence hindgut fermentation patterns.

 

Researchers also identified significant differences in microbial community composition between the two diet types at both 24 and 48 hours. In particular, an interaction involving Proteobacteria was observed at 24 hours, with levels highest in the MIX diet supplemented with the fibre-based feed. However, beyond this isolated interaction, the inclusion of the forage feed caused no substantial additional changes to the overall microbial community structure.

 

Importantly, the researchers concluded that the fibre-based feed produced “no negative effects” on fermentation parameters or microbial composition within the in vitro model. In practical terms, this suggests the feed was compatible with normal hindgut fermentation processes and did not disrupt microbial balance under the conditions tested.

 

The findings are significant because they contribute to a growing body of research examining how equine diets influence gut microbial ecology. However, the authors’ conclusions remained appropriately cautious. The study did not evaluate live horses, clinical health outcomes, performance measures, or long-term feeding effects. Instead, it provided an initial laboratory-based assessment of how a fibre-based feed interacts with hindgut fermentation systems.

 

Overall, the research suggests that inclusion of the tested fibre-based forage feed did not adversely affect hindgut microbial activity in vitro, while also highlighting the substantial influence that basal diet composition exerts on equine fermentation dynamics and microbial community structure.

 

*EquidGel®

 

For more details, see:

K.J. Hart, M.J. Hegarty, E.H. Hart,

An investigation into the impact of the inclusion of a commercial fiber-based feed, designed for both hydration and nutrition, on the equine hindgut microbiomes,

Journal of Equine Veterinary Science (2026) Vol 161, 105862,

https://doi.org/10.1016/j.jevs.2026.105862

Black soldier fly larvae for treating horse manure

Black soldier fly larvae composting manure 

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Managing horse manure remains a significant challenge for the equine industry. Large volumes
of waste are produced daily by stabled horses, and disposal can be costly, labour-intensive, and environmentally problematic. In addition to the sheer quantity of manure generated, its nutrient composition can vary widely, and it may also contain residues of veterinary medications such as moxidectin, a commonly used antiparasitic drug. These factors complicate composting and land application practices, prompting researchers to explore more sustainable and efficient waste-management solutions.

A novel study led by Yanting Guo at the University of Findlay, Ohio,  investigated whether black soldier fly larvae (BSFL) could provide an innovative biological approach to processing horse manure. The research examined the ability of BSFL to reduce manure mass while transforming nutrients into potentially useful by-products such as natural fertiliser.

Black soldier flies are increasingly attracting scientific and agricultural interest because of their remarkable waste-processing abilities. Unlike common houseflies and blowflies, black soldier flies are not considered pests to humans. Adult flies possess greatly reduced mouthparts and consume little or no food, meaning they do not regurgitate material or spread pathogens in the way houseflies commonly do. Their larvae are also substantially larger and more competitive than other fly species, often suppressing the development of nuisance flies by consuming resources before other larvae can establish themselves. As a result, BSFL-based composting systems tend to produce less odour and are generally considered more hygienic and environmentally friendly.

The study evaluated how effectively BSFL could process horse manure collected from four horses treated with moxidectin. Researchers compared larvae raised on manure with a control group fed standard chicken feed. Over the course of the experiment, the team assessed larval survival, growth rates, dry mass reduction, and nutrient transformations within the manure.

The results were highly encouraging. Black soldier fly larvae demonstrated exceptionally high survival rates of between 98 and 100 percent across all feeding substrates, indicating that horse manure, even when containing pharmaceutical residues, could successfully support larval development.

Interestingly, larvae reared on horse manure initially outperformed those fed chicken feed. During the first half of the experimental period, the manure-fed larvae achieved greater body weight and longer body length than the control group, suggesting that horse manure may provide a surprisingly effective nutritional resource for BSFL growth. Growth later plateaued during the second half of the trial, but the larvae remained healthy and viable throughout.

One of the most important findings involved waste reduction. Within just 15 days, BSFL treatment significantly reduced the dry mass and carbon content of the manure. This demonstrates the larvae’s impressive ability to rapidly break down organic waste material, potentially reducing the volume of manure requiring storage or disposal on equine properties. 

The study also revealed important changes in nutrient composition following larval treatment. Levels of total phosphorus, potassium, calcium, magnesium, zinc, manganese, and copper decreased after processing. However, several valuable nutrients — including total nitrogen, available phosphorus, sodium, sulphur, boron, and iron — were largely retained. The carbon-to-nitrogen ratio also remained relatively stable, suggesting the remaining material may still possess strong fertiliser value for agricultural use.

Overall, the findings demonstrate that black soldier fly larvae could offer a practical and environmentally sustainable strategy for managing horse manure. By simultaneously reducing waste volume and converting manure into nutrient-rich fertiliser material, BSFL systems may provide horse owners and equine facilities with an innovative approach to improving manure management while supporting circular agricultural practices.

 

For more details, see:

Yanting Guo, Victoria Ritzler, Susan Grube,

Bioconversion of horse manure using black soldier fly (Hermetia illucens) larvae: growth, waste reduction and nutrient dynamics,

Next Research (2026) Vol 9,101726.

https://doi.org/10.1016/j.nexres.2026.101726

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