The role of the lymphatic system in energy metabolism

Article by Peter Bollen, head nutritionist Cavalor

In recent years, focus has turned towards the emerging science of the lymphatic system. It is as important as the circulatory system (which includes the heart and the blood vessels), and is fundamental to the functioning of the body and central to the immune system, energy metabolism, detoxification and energy availability in the horse’s body.

A horse with a well-functioning lymphatic system can metabolise energy and clear metabolic waste more efficiently, leading to enhanced performance and faster recovery. 

So how can we tap into the benefits of an effective lymphatic system? Well, the first step is in understanding what it is. We might know that nutrients and oxygen are carried in the bloodstream towards our tissues, but what about how they are actually delivered to the cells?

This is where the lymphatic system comes in. Broadly speaking, it runs in parallel to the circulatory system and creates the point of delivery to the cells and tissues. The circulatory system carries the blood via arteries and vessels, which get smaller as they reach the muscle tissue as capillaries - where the wall is only one cell thick.  

This enables smaller molecules such as nutrients and oxygen to be pushed out of the capillaries and into the fluid around the cells - or lymph - while retaining larger cells like erythrocytes (red blood cells). 

The lymphatic system is an extensive network of vessels and nodes that transports lymphatic fluid around the body and it has two main functions:

1. Energy metabolism - transporting nutrients and oxygen to the cells

All the cells and tissues of a horse’s body are surrounded by a watery gel-like substance called interstitial fluid. This provides a medium for dissolved oxygen and nutrients to travel across to the cells. Lymph capillaries, carrying these substances, run through the interstitial fluid. The walls of these capillaries are also only one cell thick and have overlapping junctions, which make them highly permeable and allow easy transfer of materials.

In practical terms, this means the horse’s muscles and tissues get all the energy they require to carry out all their metabolic processes. As well as being responsible for giving cells the oxygen and nutrients they need, the interstitial fluid transports salts, hormones, neurotransmitters, coenzymes, amino acids, sugars and fatty acids around the body via the lymphatic system.

“A horse with a well-functioning lymphatic system can benefit from increased energy and enhanced performance, but without feeling too fresh or fizzy”

2. Detoxification: processing waste products

During the season, horses are placed under physiological demands and their body has a lot to process. In hard exercise and in races, their body will produce a lot of waste products. Their thin-walled lymph vessels also allow interstitial fluid into them to remove the waste products of cell metabolism (such as cell debris, bacteria, dead blood cells, pathogens, toxins, lactic acid and protein molecules) from each cell. This process is just as important as carrying necessary materials to the tissues to provide energy. 

These metabolic waste products are carried in the lymph away from the cells for detoxification. This is the term used for the continuous processes in the horse’s body to remove those waste products or metabolites that are naturally produced.

Detoxification takes place mainly in the liver, kidneys and intestines, so it is really important to ensure that those organs in the horse are healthy and functioning well. By supporting the liver and kidneys, you can help this breakdown process and allow the horse to better metabolise compounds that would otherwise be toxic if they remained in the body.

Gut health is also very important to the lymphatic system and detoxification, given that more than half of the lymphatic vessels of the horse are located within the gastrointestinal tract. 

Peristalsis (the natural contraction and relaxation of the gut wall) drives the return of lymph to the rest of the body. Movement in the gut is stimulated by food consumption (mainly long fibres) and is crucial to lymphatic system function as there is very limited muscular contraction in the horse’s lymphatic vessels themselves. This means it relies on passive forces from movement of other systems in the horse’s body as opposed to active muscle contractions.

Ensuring sufficient feed for a horse around the clock is crucial, not only for maintaining gut health, but to maintain a healthy immune system and detoxification process as well.

Lymphatic system and immune function

In addition to lymph and lymph vessels, the horse has around 8000 lymph nodes. These bundles of lymphoid tissue and proteins act as a filter for foreign substances that travel through the lymphatic fluid and contain lymphocytes (white blood cells) that help the body fight infection and disease. This means that the lymphatic system is also key to the functioning of the immune system.

As the lymph tissue approaches each lymph node, it slows down and collects in that area. Horses have so many lymph nodes that they are extremely susceptible to lymph node blockage. Lymph nodes can actually be felt or sometimes seen at various points around the horse’s body, particularly around the head and neck or when they are swollen.

Keep on moving

Movement is so important for horses, precisely because of the fact that there are no direct muscular contractions within the walls of the lymph vessels to promote the flow of lymph. The functioning of their lymphatic system relies on the force of movement of other structures in the body, such as the movement of the skin to apply pressure to the underlying tissues and stimulate the transport of lymph through the vessels.

In the modern day, racehorses can be stabled for longer periods of time. It is very common to see leg swelling, which has a very simple explanation in terms of the immune system. This principle of continuous movement being necessary applies especially to the legs, where this elastic movement of the skin is assisted by a pump mechanism in the hoof and fetlock joint. It is thought that this is the case due to there being no muscles in the lower limbs of the horse to aid the movement of lymph from this area.

Horses therefore need to move extensively and perhaps almost constantly (up to 16 hours per day) to keep the lymph circulating around the body, and standing still for too long significantly impairs the functioning of the lymphatic system.

Practical tips for a healthy lymphatic system

1. Turn horses out as much as possible  

Horses that are standing still for long periods of time are at risk of an impaired lymphatic system, which can impact the immune system, recovery time and ultimately performance. Turnout makes a happier horse and a healthier horse.

2. Cool down for at least 15 minutes after exercise

The period of time immediately after training is important for removal of metabolic waste products and keeping a horse moving after a hard training session stimulates the lymphatic system to continue to remove waste products from cells, which includes the removal of lactic acid. By cooling down properly after every session, you can significantly improve recovery times.

3. Consider feeding supplements that can directly benefit the lymphatic system

Functional herbal ingredients in innovative supplements can support lymphatic system function. Cleavers (Galium aparine) is known to bring benefits to the lymphatic system. Couch grass (Elymus repens), Nettle (Urtica dioica), and Dandelion (Taraxacum officinale) are all known to have purifying effects which can support metabolism and detoxification.

Even Lionel Messi, Usain Bolt or Iga Swiatek have picked up issues through their sporting careers, despite having elite support teams behind them. Unfortunately injuries do just happen, but with foresight, preparation and providing the best nutritional support to their horses, trainers will give themselves the greatest chance of avoiding yet another bad news phone call to an owner.

Probiotics – The key to a well-balanced equine gut

By Kerrie Kavanagh

It is no surprise that the health maintenance of the racehorse is a top priority for trainers. And probiotics can be used as a treatment modality to manipulate the gut microbiome to improve or maintain health. Equine studies to date have shown that probiotic strains can offer an advantageous approach to minimising disturbances in the gut microbial populations, repair these deficiencies—should they occur—and re-establish the protective role of the healthy gut microbiome. Other probiotic-associated health benefits include reducing diet-related diseases such as colic and laminitis, preventing diarrhoea, conferring host resistance to helminth infection, improving stress-related behavioural traits (e.g., locomotion) and even promote the development of an effective gut-brain communication pathway. 

Probiotics have been used by humans for more than 5,000 years with their development closely linked to that of dairy products and fermented foods. Today, probiotics are seen as an excellent non-pharmaceutical way to improve the health of both humans and animals, and there are a plethora of products to choose from. But what exactly is a probiotic, and how do they work? Why would your horse need one? What types of probiotics are available for horses? These are all questions that horse trainers ask frequently, which we will attempt to answer here. 

The Equine Gut Microbiome

Probiotics and the equine microbiome can benefit from a valuable symbiotic relationship; probiotics are seen as a restorative treatment modality for the gut, to re-establish the bacterial populations there and also to re-establish the protective role that the health gut microbiome confers to the host. But when we discuss the equine microbiome, what are we really talking about? 

The gut microbiota/microbiome can be categorised by anatomical location such as the oral microbiota/microbiome in the mouth and the intestinal microbiota/microbiome in the intestines, etc. Therefore, the gut microbiome pertains to the microbiota in the gastrointestinal tract. This population of microorganisms (bacteria, fungi, viruses, protozoa) is referred to as the ‘microbiota’ of the gut, while the term ‘gut microbiome’ refers to the genetic material associated with these microorganisms. The microbiome can be defined as the sum of the microbes and their genomic elements in a particular environment. If we look at the definition of the microbiome having the propensity to an equation, then any equation must be balanced; to maintain that balance is key. If the microbial community exists in an environment in a balanced state, then any upset or disturbance to the microbial populations will cause the balance to shift (known as dysbiosis). To maintain the balance, we need to firstly understand the way the microorganisms exist within their community (i.e. their microorganism-to-microorganism interactions and also microorganism-to-environment interactions) and secondly, their functioning role. If we can understand their (microorganism) position and role, then we can maintain the balance or re-establish the balance if a shift occurs.  

Fig. 1 Factors that can lead to gut Dysbiosis

The human intestinal microbiome is now recognised as an organ and likewise, the equine intestinal microbiome is deemed an ‘organ’ of the body and is vital for the breakdown of complex food and subsequent release of energy, protection against the pathogenic bacterial colonisation and in regulating the immune system and metabolic functions. There has been much debate regarding the content of the healthy equine microbiome, and even to deduce what ‘healthy’ or ‘normal’ is requires a level of understanding of the microbiota associated with healthy horses. This question has been posed by many researchers and frankly has yet to be answered with certainty. There are many reasons why the ‘normal’ microbiota keeps eluding us; and this can be attributed to the many reasons as to why the gut microbiota (of a healthy horse) can be affected (see Figure 1). It is thought that the diversity of the human gut microbiota and the general assembly of microbial communities within the gut (with the dominant phyla being classed as belonging to Firmicutes and Bacteroidetes) is a shared hypothesis across most species (i.e., humans and animals share a similar gut microbiome structure). Firmicutes and Bacteroidetes have been shown to constitute the main dominant phyla in equine, bovine, canine and feline gut microbiome studies indicating the cruciality of the role they play in the maintenance of a healthy microbial ecology in the gastrointestinal tract. Several studies do agree that dominant phyla of the equine gut microbiota are obligate anaerobes: the gram-positive Firmicutes and the gram-negative Bacteroidetes; other phyla are identified as Proteobacteria, Verrucomicrobia, Actinobacteria, Euryarchaeota, Fibrobacteres and Spirochaetes. Ninety-five percent of the  Firmicutes phyla contains the Clostridia genus in addition to genera related to gut health such as Lachnospiraceae, Faecalibacterium and Ruminococcaceae. The other main dominant phyla, Bacteroidetes, on the other hand contains a large variety of the genus. 

Role of the Equine Gut Microbiota

The role of the gut intestinal microbiota serves to protect and prevent disease. The gut microbiota has several purposes: prevention of pathogen colonisation by competing for nutrients, enrichment and maintenance of the intestinal barrier—their ability to renew gut epithelial cells and repair damage to the mucosal barrier, the breakdown of food and releasing energy and nutrients, such as synthesising vitamins D and K and also conserving and restoration of the immune system by the formation of antimicrobial metabolites and blocking access to the binding sites of the mucosal wall. The gut microbiota is also thought to play some role of influencing the neuro-active pathways that affect behaviour. It is not surprising to see that gut disorders and gastrointestinal diseases can arise when gut dysbiosis occurs. The role of the gut microbiota may have even more importance than is realised and may have a role to play with developing illness or disease later in life.

The microbial colonisation of the intestinal tract begins at birth. The foal begins its colonisation through contact with the microbiota of the mare’s vaginal and skin surfaces plus the surrounding environments to which the foal is exposed and reaches a relatively stable population by approximately 60 days in age. It is perhaps a fight for dominance to achieve establishment in the gut among the bacterial populations that sees the foal’s microbiota as being more diverse and quick to change when compared to that of the older horse. The subsequent colonisation of the intestinal tract will reflect the foal’s diet, changing environment, introduction to other animals, ageing and health.

What exactly is a probiotic?

Beneficial bacteria can be isolated and harvested to prepare a bespoke probiotc

The word ‘probiotic’ is of Greek origin meaning ‘for life’ and the WHO/FAO have defined probiotics as ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’.  People have long believed that exposure to non-pathogenic microorganisms can benefit the health of humans and animals. The thinking behind this is that daily consumption of sufficient numbers of ‘good’ microorganisms (either bacteria or fungi) can maintain a healthy population of microorganisms in the gut and benefit overall health.  

Probiotics are used to manipulate the bacterial populations of the gut in order to re-establish the delicate microbial balance there which, in turn, confers health benefits on the host. As the benefits associated with some of the ‘good’ bacteria within the gut became known, these were referred to as probiotic bacteria. 

How do probiotics work?

There are 4 main mechanisms by which probiotics are thought to exert their effects.

1. By inhibiting pathogen colonisation in the gut through the production of antimicrobial metabolites or by competitive exclusion; in other words, they prevent the ‘bad’ bacteria from growing in the gut.

2. By protecting or re-stabilising the commensal gut microbiota, probiotics can be a means to re-establish the balance of the gut microbial populations.

3. By protecting the intestinal epithelial barrier, they maintain the health of the intestinal wall.

4. By inducing an immune response, probiotics can boost the immune response and help prevent disease.

If we consider the definition of a probiotic as ‘live non-pathogenic microorganisms that, when administered in adequate amounts, confer a health benefit on the host’, then this reference to ‘adequate amounts’ must be emphasised, and the dose administered is critical to ensure that the probiotic has the desired effect. For horses, we must consider the route through the digestive tract that the probiotic strains must travel to arrive at their destination is a distance over 15 metres long. It is a race for survival! The gastrointestinal system has many obstacles along the passage such as the acidic stomach environment and the dangers of exposure to bile and digestive enzymes, in which they must survive. The initial dose of ‘live’ probiotic strains is therefore crucial to ensure survival in the gut. Prebiotics are ingredients such as carbohydrates and fibre, which promote the growth of these probiotic bacterial/yeast strains in the gut. Prebiotics are essentially the food for the probiotic strains and can help form a symbiotic relationship with the probiotic to improve the overall health status of the horse. 

Why would you need to give your horse a probiotic?

Gut dysbiosis is a fluctuation or disturbance in the population of microorganisms of the gut, which may be linked to a wide range of diseases in horses. Gut dysbiosis can be caused by many factors ranging from dietary changes, antibiotics, disease, intense exercise and training, age, worms, environment, travel, or even minor stress events—resulting in major consequences such as colic. Dysbiosis is generally associated with a reduction in microbial species diversity. 

Diet is one of the major factors contributing to gut dysbiosis. Unlike the ruminant cattle and sheep that use foregut fermentation, horses are hindgut fermenters. The large intestine is the main area where fermentation occurs. The horse utilises the microbial enzymes of the hindgut microbial population in the colon and caecum to break down the plant fibres (cellulose fermentation) sourced mainly from grasses and hay. The horse itself does not possess the hydrolytic enzymes that are required to break the bonds of the complex structures of the plant carbohydrates (in the form of celluloses, hemicelluloses, pectins) and starch; so therefore, it strongly relies on the microbiota present to provide those critical enzymes required for digestion. The main phyla Firmicutes and Bacteroidetes possess enzymes capable of breaking down the complex carbohydrates (such as starch and cellulose). Research has shown that forage-based diets (grasses and hay) promote the most stable gut microbiomes, but ultimately the equine athlete requires far more energy than a forage-based diet can supply. Supplementing the diet with concentrates containing starch such as grain, corn, barley and oats can affect the number and type of bacteria in the gut. Optimising diet composition is so important as carbohydrate overload—as seen with high-starch diets (>1g/kg body weight per meal)—can change the populations of bacteria in the gut, alter pH, upset digestion and the gut environment, and ultimately result in diseases such as colitis, colic and laminitis. The correct diet is essential for maintaining the delicate balance of bacterial populations. Probiotics can be used to either replace the bacteria missing in the gut and/or can help maintain the delicate microbial balance even in the face of adversity such as abrupt dietary changes, antibiotic treatment and stress.

What types of probiotics are available for horses?

There are several probiotic products on the market, and most are in powder or liquid form. There are two main categories of probiotics: generic and autogenous. Generic probiotics are off-the-shelf products that contain specific strains of bacterial or yeast, singularly or in combination. The Lactobacillus and Bifidobacterium families, Enterococci and yeasts such as Saccharomyces cerevisae and boulardii are the most common equine probiotic strains. Advantages of generic probiotics are that they are widely available, easy to administer, and they may be beneficial to horse health (if the strains are alive in sufficient numbers). Autogenous probiotics are specifically formulated using bacteria obtained from the horse’s own faecal sample and, as such, are uniquely adapted to that individual animal. These host-adapted bacteria are more likely to survive in the gut than non-adapted generic strains and can quickly replenish absent or low levels of bacteria unique to the individual horse, thus maintaining health.

Gut Health - Aspects of bad behaviour and how to fix it

By Bill Vandergrift, PhD

When performance horses behave or react in ways that are less than desirable, we as trainers and handlers try to figure out what they are telling us.  Is there a physical problem causing discomfort, or is it anxiety based on a previous negative experience? Or, is the bad behaviour resulting from a poor training foundation leading the horse to take unfamiliar or uncomfortable situations into their own hands? This usually triggers the fright and flight reflex instead of relying on the handler for direction and stability.  

Often when the most common conditions that cause physical discomfort are ruled out, it may be tempting to assume that the bad behaviour is just in the horse’s head or that the horse is just an ill-tempered individual. In my experience, most unexplainable behaviour expressed by performance horses is rooted in the horse’s “other brain,” otherwise known as the digestive system. In this article, I will explain what causes poor digestive health, the link between digestive health and brain function, and what steps can be taken to prevent and/or reverse poor digestive health.

Digestive health

While most trainers are familiar with gastric ulcers, symptoms and common protocols utilised to heal and prevent them, there still remains a degree of confusion regarding other forms of digestive dysfunction that can have a significant effect on the horse’s performance and behaviour. In many cases, recurrent gastric ulcers are simply a symptom of more complex issues related to digestive health.  Trainers, veterinarians and nutritionists need to understand that no part of the horse’s digestive tract is a stand-alone component. From the mouth to the rectum, all parts of the digestive system are in constant communication with each other to coordinate motility, immune function, secretion of digestive juices and the production of hormones and chemical messengers. If this intricate system of communication is interrupted, the overall function of the digestive system becomes uncoupled, leading to dysfunction in one or more areas of the digestive tract.

For example, a primary cause of recurrent gastric ulcers that return quickly after successful treatment with a standard medication protocol is often inflammation of the small and/or large intestine. Until the intestinal inflammation is successfully controlled, the gastric ulcers will remain persistent due to the uncoupling of communication between the stomach and lower part of the digestive tract.

How do we define digestive health? Obviously, digestive health is a complex topic with many moving parts (figuratively and literally). The main parts of a healthy digestive system include, but are not limited to 1) the microbiome, 2) hormone and messenger production and activity, 3) health of epithelial tissues throughout the digestive system, 4) normal immune function of intestinal tissue and 5) proper function of the mucosa (smooth muscle of the digestive tract) to facilitate normal motility throughout the entire length of the digestive tract.

Microbiome is key

A healthy and diverse microbiome is at the centre of digestive health. We now recognise that reduced diversity of the microbiome can lead to digestive dysfunction such as colic and colitis, development of metabolic disorders such as insulin resistance, reduced performance and increased susceptibility to disease. Research efforts leading to greater understanding of the microbiome have recently been aided by developing more sophisticated techniques used to identify and measure its composition in horses, laboratory animals, pets, livestock and people. While these research efforts have illustrated how little we really understand the microbiome, there have been significant discoveries stemming from these efforts already.  For example, a specific bacteria (probiotic) is now being used clinically in people to reverse depression resulting from irritable bowel syndrome (IBS). Bifidobacterium longum NCC3001 reduces depression in IBS patients by directly affecting the activity of the vagus nerve which facilitates communication between the brain and the digestive tract. It should be noted that Bifidobacterium longum NCC3001 has been demonstrated to be more effective at reducing depression in IBS patients than antidepressant drugs commonly used in these same cases. While we do not commonly recognise clinical depression as a physiological condition in horses, the same mechanisms that affect the function of the vagus nerve and brain chemistry in IBS patients can affect a horse’s behaviour and reactivity due to intestinal dysfunction, resulting in a horse that bites, kicks, pins its ears or otherwise demonstrates hyper-reactivity for no apparent reason, especially if this behaviour is a recent development.

One case in particular I dealt with years ago that had underlying suggestions of depression in a horse, and underscores the importance of a diverse and healthy microbiome for performance horses, was a horse that had been recently started in training and was working with compliance on the track. The problem was this horse seemed to be unable to find the “speed gear.” The trainer had consulted with various veterinarians, physical therapists, chiropractors and others in an attempt to pinpoint the cause for this horse’s apparent inability to move out; and it was everyone’s opinion that this particular horse had the ability but he simply wasn’t displaying the desire. In other words, he was “just dull.”  After reviewing this horse’s case and diet, I had to concur with everyone else that there was no obvious explanation for the lack of vigor this horse displayed on the track even though his body condition, muscle development and hair coat were all excellent. Despite any outward signs of a microbiome problem other than the horse’s “dullness,” I recommended a protocol that included high doses of probiotics daily, and within 10 days, we had a different horse. The horse was no longer dull under saddle; and when asked to move out and find the next gear, he would readily comply; by making an adjustment to the microbiome, this horse’s career was saved.

There is always a change to the microbiome whenever there is a dysfunction of the digestive system, and there is always digestive dysfunction whenever there is a significant change to the microbiome. Which one occurs first or which one facilitates a change in the other may be dependent upon the nature of the dysfunction, but these two events will almost always occur together. Therefore, efforts to maintain a viable and diverse microbiome will reduce the chances of digestive dysfunction and increase the speed of recovery when digestive dysfunction occurs.

Leaky gut

Even though the physiological basis of leaky gut has been understood for some time, leaky gut has not been a condition recognised to affect behaviour, performance or health in horses until recently. Today, leaky gut is quickly becoming a recognised dysfunction of the digestive system that has a multitude of negative effects on the overall well-being of horses including allergies, insulin resistance, uncharacteristic behaviour, picky appetite and reduced performance. As illustrated in Figure 1, leaky gut refers to a breakdown of the structures, referred to as tight junctions that hold adjacent intestinal cells together.

When the small and large intestines are healthy, the tight junctions between individual intestinal cells remain closed, forming a barrier between the inside of the intestinal lumen and the inside of the horse’s body. This barrier normally serves as a very important function by preventing complex molecules such as undigested proteins and carbohydrates as well as pathogenic and non-pathogenic bacteria from “leaking” through the intestine and entering the horse’s blood stream. Also note in Figure 1 that as you move your focus from left to right in the diagram, not only do the tight junctions become open, but the intestinal cells become more and more inflamed, eventually leading to total breakdown of the intestinal cells themselves. At this point, you not only have leaky gut, but now the condition has progressed from a leak to a flood, so to speak. This illustrates that the severity of leaky gut can vary from mild to severe with increasing severity also being associated with increasing intestinal inflammation.

Figure 1. Basic Physiology of Leaky Gut

 Image Courtesy of Kemin Industries.

As the severity of leaky gut increases, the communication between the different components of the digestive system is disrupted, and the coordination between the different sections of the digestive tract becomes uncoupled. The production of hormones such as serotonin and dopamine is altered, which has a direct effect on digestive function and brain function concurrently. This is one of the most obvious reasons why intestinal inflammation causes a horse’s behaviour and temperament to change.  Inflammation of intestinal cells initiates a self-propagating process that stimulates additional inflammation of the intestine and initiates systemic inflammatory processes throughout the entire body.  The self-propagating nature of intestinal inflammation is the reason why horses don’t just simply recover from it without assistance. In fact, I have worked with individual horses that have suffered from leaky gut for years based on their case history. The longer leaky gut has existed, the longer it will take to reverse in most cases.

In addition to leaky gut causing changes in behaviour and performance, leaky gut can also alter immune function and metabolic status. There is growing evidence that the initial cause of insulin resistance in many horses is in fact leaky gut. Intestinal inflammation causes a marked change in glucose homeostasis, which in turn reduces insulin sensitivity. Unfortunately, it appears that once insulin resistance is established, it is near impossible to reverse completely even if the leaky gut condition that caused it in the first place is successfully reversed.  

Leaky gut is also a common trigger for allergies in horses. It is well known that the majority of the horse’s immune system is located in the intestine. When the intestine “leaks,” undigested proteins, bacteria and other immune-stimulating agents gain access to the bloodstream, thus putting the immune system on high alert. Many horses respond to this situation by presenting with multiple allergies, many of which are reactive enough to warrant immunotherapy (allergy shots). I often hear in these situations that “my horse is allergic to everything”; and in many instances, this would seem to be the case. Fortunately, by reversing leaky gut and removing these immune-stimulating agents from the horse’s body, many of these allergies simply disappear. Keep in mind that horses can in fact be truly allergic to certain feeds and environmental agents, and these allergies have nothing to do with digestive health. It is best to consult with an experienced veterinarian and nutritionist to distinguish between true allergies and those caused by an overactive immune system triggered by leaky gut.

As illustrated in Figure 2, leaky gut can be caused by many different “triggers.” In performance horses, the most common triggers for leaky gut are: 1) stress (physical and emotional), 2) intense exercise, 3) heat stress and 4) various medications. Of these, stress is the strongest trigger for leaky gut due to the fact that stress of any kind increases circulating levels of cortisol. Cortisol breaks down the tight junctions of the intestine, which in turn results in leaky gut.

Figure 2.  Possible Factors Causing Leaky Gut in Horses

Preventing and reversing leaky gut

Almost all performance horses will present with digestive dysfunction or leaky gut at some point in time in their career. The reason is simple: stress is the strongest trigger for leaky gut, and all performance horses experience stress to one degree or another. Unfortunately, there is no exclusive marker for leaky gut at the present time. Researchers are getting close to developing a reliable diagnostic test for leaky gut as this article is written, but in the meantime it is best to detect digestive dysfunction and leaky gut by evaluating changes and observing symptoms presented by the horse. A partial list of symptoms to look for includes: a) not performing to the previous level or level that is expected, b) change in personality (e.g., grouchy or “leave me alone” behaviour, c) resistance to leg aids especially on right side (right dorsal colon is often inflamed), d) backing ears or biting when being saddled especially when the cinch is tightened, e) dull, f) prefers to eat hay rather than grain, g) manure has a funny odor or consistency, h) low fecal pH (herd specific), i) constantly shifting weight from one hind leg to the other in the stall, j) tight and “sunk in” in flank area, k) tight in back and hamstrings, l) eating a lot of grain but not gaining weight, m) dull coat and/or skin disorders, n) poor hoof quality, o) multiple allergies, p) improves while on omeprazole but quickly reverts when taken off, q) recurrent or chronic diarrhea and r) irreconcilable behaviour. (Note: No two horses will present with all of these symptoms or the same symptoms, but this list provides a guide for the most common symptoms to evaluate.

Since stress is the strongest trigger for intestinal inflammation and leaky gut, steps should be taken to remove as much stress as possible. For example, paying attention to biosecurity measures, transporting at times and with methods that reduce stress, adjusting training schedules to avoid heat stress and overexertion are things that can be done to reduce stress. Keeping forage (hay and/or pasture) in front of horses 24/7 is critical. Controlling the amount of grain-based feed fed per day can help in many cases. As a guideline, if you are having to feed more than 7 kgs (or 15 lbs) of grain per day to maintain a horse’s condition and energy level, you should suspect digestive dysfunction as one of the reasons so much feed is required.

If you suspect your horse is presenting with leaky gut, how can you help reverse it? Begin by continuing to provide “good quality” forage 24/7 and utilise a high-fibre, high-fat, low-soluble carbohydrate feed in place of a grain-based feed.

Second, utilise nutritional tools that are now available to stimulate closure of the tight junctions. These include nutraceuticals such as butyric acid, glutamine, bioactive peptides (plasma or colostrum), specific probiotics such as Bacillus subtillus PB6 and carnitine. There are products available currently that provide one or more of these nutraceuticals in the proper dosage.

Third, support a diverse and healthy microbiome with the use of probiotics and prebiotics. When selecting probiotics, numbers matter! It is preferred that any probiotic strain be dosed at a minimum of 1 billion CFUs (colony forming units) per day. Be sure to understand that this is per strain and not cumulative for a mixture of different probiotic strains. I would rather administer 10 billion CFUs of a single probiotic strain than 5 billion CFUs of a product containing a mixture of seven different strains.  Additionally, for optimal effectiveness of any probiotic, it is imperative that it be dosed in combination with prebiotics such as yeast cultures, mannan-oligosaccharides, fructooligosaccharides, or inulin, for example. Prebiotics and probiotics work synergistically to alter the diversity and overall activity of the microbiome in a manner that provides far superior results compared to either one by itself.

Fourth, provide anti-inflammatory activity to the intestine with omega-3 fatty acids. Flaxseed, chia seed, hemp oil, and fish oil all contribute to reducing inflammation in the intestine. The omega-3 fatty acid EPA from fish oil is especially effective as an anti-inflammatory agent for the intestine. DISCLAIMER:  In cases of severe leaky gut and severe intestinal inflammation, omega-3s may exacerbate the inflammation rather than reduce it. This will be noted within just 2–3 days by the horse presenting with notable diarrhoea. Additionally, omega-3s and coconut products are contraindicated for horses presenting with severe or chronic diarrhoea, as this is usually a reliable symptom of severe leaky gut, which is often made worse by these dietary components.

Fifth, include nutraceuticals to improve production of intestinal hormones and provide additional protection for intestinal cells. Possible choices include liquorice, slippery elm, aloe, arginine, citrulline, theanine, tryptophan, or alpha lipoic acid. Consult with a reputable supplement company for suggestions on which products and dosage are appropriate for your horse.

No guts, no glory!

By Catherine Rudenko

Can we increase the efficiency of the digestive system through dietary and supplementary manipulation in order to alter performance and recovery? 

The idiom ‘no guts, no glory’, when taken in the literal sense, is quite an appropriate thought for the racehorse. The equine gut is a collection of organs, which when in a state of disease, causes a multitude of problems; and when functioning effectively, it is key for conversion of food to fuel and maintaining normal health. 

In the same way we consider how fuel-efficient our car engines are, what power can be delivered and the influence of fuel quality on function, we can consider the horses’ digestive anatomy. The state of the ‘engine’ in the horse is critical to the output. What is fed or supplemented, and the manner in which we do so, has fascinating and somewhat frightening effects on efficiency and recovery. 

We now, in a human context, have a much better understanding of the relationship between the gut and states of disease. Before disease in a notable sense is present, we see loss of function and reduction in performance. With equines, in recent years, the focus has fallen toward ulceration and the stomach. Now interest is growing into the small and large intestines, looking at factors that influence their performance and in turn how this affects performance on the track. 

In order to consider how we can positively influence gut function, first we need to understand its design and capability, or lack of capability which is more often the problem. The horse, by definition, falls into the category of a large non ruminant herbivore—the same grouping as rhinoceroses, gorillas and elephants. The horse is well designed for a fibre-based diet, as reflected by the capacity of the large intestines, yet we must rely heavily on the small intestine when feeding racehorses. Health and function of both small and large intestines are important and are connected. 

Small Intestine 

The small intestine is a relatively short tube of approximately 25m in length—the same length as found in sheep or goats. The primary role of the small intestine is the digestion of protein, fats and carbohydrates. The workload of this organ is significant and is also time constrained, with feed typically moving at a rate of 30cm per minute (1). The rate of passage is highly influenced by whether the stomach was empty before feeding, or if forage has recently been consumed. The advice of feeding chaff with hard feed is in part to the slow rate of passage and give further time for the processes of digestion. 

The mechanisms for digestion in the small intestine include pancreatic juices, bile and enzymes. Of particular interest are the various enzymes responsible for digestion of protein and carbohydrates— the key nutrients often considered when choosing a racing diet. The ability to digest carbohydrate, namely starch, is dependent on two factors: firstly, form of starch and the level of alpha-amylase—a starch-digesting enzyme found in the small intestine. Whilst the horse is quite effective in digestion of protein, there are distinct limitations around digestion of starch. 

Starch digestion, or lack of digestion in the small intestine, is the area of interest. When feeding, the aim is to achieve maximum conversion of starch in the small intestine to simple sugars for absorption. This is beneficial in terms of providing a substrate readily available for use as an energy source and reducing the ill effects seen when undigested starch moves into the next section of the digestive tract. Alpha-amylase is found in very limited supply in the equine small intestine—the amount present being only approximately 5% of that found within a pig. Despite a low content, the horse can effectively digest certain cereal starches, namely oats, quite effectively without processing. However, other grains commonly used, (e.g., barley and maize [corn]), have poor digestibility unless processed. Flaked, pelleted or extruded cereals undergo a change in starch structure enabling the enzyme to operate more effectively. 

Processing grains whilst improving digestion does not alter the amount of enzyme present in the individual. An upper limit exists on starch intake, after which the system is simply overloaded and the workload is beyond the capacity of the naturally present enzymes. The level is estimated at 2g starch per kilogram of bodyweight in each meal fed. In practice, this translates to 3.5kg (7 ¾ lbs) of a traditional grain-based diet of 28% starch. In bowls, this is roughly 2 bowls of cubes or 2 ¼ bowls of mix—an intake typical of an evening feed. The ‘safe limit’ as a concept is questionable because of other factors involved in starch digestion, including how quickly a horse will eat their feed, dental issues and individual variation in the level of alpha-amylase present. 

In practice, feeding racehorses will invariably test the capacity of the small intestine as the volume of feed required to meet the demands of training is significant, and through time constraints of both horse and human results in a large-sized evening meal. The addition of amylase or other enzymes to the diet is therefore of interest. Addition of amylase is documented to increase digestion of maize (corn)—one of the most difficult grains to digest—from 47.3% to 57.5% in equines (2). Equally, wheat digestion has been evidenced to improve with a combination of beta-glucanase, alpha-amylase and xylanase in equines, increasing starch digestion from 95.1% to 99.3% (3).

Use of enzymes in the diet has two areas of benefit: increasing starch conversion and energy availability, and reducing the amount of undigested starch that reaches the hindgut. The efficacy of the small intestine directly impacts the health of the large intestine—both of which influence performance. 

Large Intestine 

The caecum and colon, of which there are four segments, form the group referred to as the hindgut. Their environment and function are entirely different to that of the small intestine. Here, digestion is all about bacterial fermentation of the fibrous structures found in forages and parts of grains and other feed materials. The time taken to digest foodstuffs is also significantly different to that of the small intestine, with an average retention time of 30 hours. 

The end result of fermentation is the production of fatty acids, namely acetate, butyrate and propionate—the other by-product of fermentation being lactate. The level of fatty acids and lactate produced is dependent on the profile of bacteria found within the gut, which in turn react to the type of carbohydrate reaching the hindgut. There are markedly different profiles for horses receiving a mostly fibre-based diet compared to those with a high-grain intake. 

The interaction between the microbial organisms and metabolism, which directly influences health and disease, is gaining greater understanding. By looking at the faecal metabolome, a set of small molecules that can be identified in faecal samples, and the categories of bacteria in the gut, it is possible to investigate the interaction between the individual horse, its diet and bacteria. Of course, the first challenge is to identify what is normal or rather what is typical of a healthy horse so that comparatives can be made. Such work in horses in training, actively racing at the time of the study, has been carried out in Newmarket. 

Microbiome is a term used to describe microorganisms, including bacteria, that are found within a specific environment. In the case of the horses in training, their microbiome was described before and after a period of dietary intervention. The study evidences the effect on the hindgut of including an enzyme supplement, ERME (Enzyme Rich Malt Extract). The table below shows changes in nine bacterial groups before and after supplementation. 

Along with changes in bacterial abundance, which were relatively small, came more significant changes within the metabolome. The small molecules found in the metabolome are primarily acids, alcohols and ketones. Of particular interest, and where statistical significance was found, were changes in acetic acid and propionic acid evidencing an effect on the digestive process. 

Whilst production of fatty acids is desired and a natural outcome of fermentation, further work is needed to determine what is an optimum level of fatty acid production. This study of horses in training is an interesting insight into an area of growing interest. 

Effects on Performance & Large Intestine Function…

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