How to choose the most effective supplements to support your horse
Good horse people want to do the right thing for the horses in their care. They want to help them perform to the best of their ability, and they want to help them to do that consistently, throughout the racing or competition season. Nutrition is a vital part of that. Every season, stables are presented with a long list of supplements, and every rep says theirs is the best. How do you know if you need to spend money on supplements, at all? If you conclude that you do, how do you sort the wheat from the chaff and pick the best one?
There are, essentially, only three reasons to feed a supplement:
To improve the balance of the daily ration,
To fill the gap between good daily nutrition and the increased requirements of horses under stress, and
To address specific health concerns.
Daily Ration Balance
First, remember that horses’ guts have adapted to digest roughage, and they need it. Hay (or grass, if you are lucky enough to have it) is the basis of a good daily ration.
You only need to feed a concentrated feed (the stuff you buy in a bag, like a Racehorse or Stud Farm Mix) to meet the additional protein, energy, vitamin, and mineral requirements that horses in work, growing, or breeding have. If the concentrate feed you choose has been prepared by a major feed company, it will generally be balanced for those things already, and they will essentially meet the daily needs of horses, when fed with forage. If you are having to correct deficiencies of energy or protein in your daily feed, consider picking a better-balanced concentrate feed for your particular horses.
In some parts of the world, grass isn’t plentiful, so forage is generally fed in the form of hay or green feed. Depending on the type of hay you choose, calcium and phosphorus balance might have to be adjusted with a daily supplement. You should ask your nutritionist or veterinarian to help you to get that right. In general, though, grains are high in phosphorus and low in calcium. Lucerne (Alfalfa) is high in calcium, while grass hays are generally lower in it. Feeding a mixture of grass hay and Lucerne as the main part of your daily ration, will likely mean that calcium and phosphorus will be close to right in your total ration, including the right concentrated feed. As an added bonus, Lucerne is a very good source of cost-effective and bioavailable protein for horses.
If you don’t need to add other stuff to your daily ration, don’t. With a few exceptions, it’s money wasted. Adding individual nutrients can produce no results or disrupt the balance of a good feed and actually have negative results.
Exceptions to the Rule
If the daily ration has selenium provided in an inorganic form, such as sodium selenite or selenate, have your veterinarian check blood selenium. Some horses will absorb and use those forms of selenium well, and others might not. Selenium has a very narrow therapeutic range (the amount they need is only a little bit less than the amount that is toxic), so it’s dangerous to over-supplement. If some horses need more, pick a supplement that provides selenium in an organic form like selenomethionine or selenocysteine. Yeast-based selenium is mostly a mixture of the two.
In a hot climate, some additional table salt or a salt block will be needed. Every horse, even spelling ponies, need access to a salt block.
Stabled horses and those in the Middle East don’t always get much grass. If horses aren’t getting fresh, growing grass, vitamin C might be low. Although it is often included in prepared feeds, it can be unstable, especially in hot climates, and levels can quickly drop. You might consider supplementing with vitamin C when horses are under extra stress. Vitamin C and the B group vitamins are water soluble, and they are not stored in the body. As a result, it makes more sense to provide those in supplements, given only when horses are under extra stress and requirements are increased.
When horses are under the added stress of hard work, transport, racing, competition, high heat and humidity, or ill health, requirements for many nutrients are increased. Feeding a daily ration designed for horses in hard work will generally provide energy, protein, fat soluble vitamins, and mineral levels to meet their overall needs, but some nutrient requirements will be increased beyond that, just at the time horses are under stress. B vitamins, for instance, will be needed in doses between 20 and 200 times requirements during times of added stress. If they were fed doses at this level on a daily basis, much of the dose would pass out in the urine. That is money wasted. On days they are travelling, racing, or sick, they would need more, absorb it, and use it. That’s money well spent.
At the same time as horses are under extra stress and need more nutrients, they will often go off feed and drink less than usual. Supplements will certainly be helpful, at those times, to fill the gap between good daily nutrition and the amount of nutrients they are eating and drinking voluntarily.
When you need a supplement for times of increased stress, it’s really important to read labels carefully. Ask yourself, these questions:
Does it have the right stuff? Is it complete?
Is the balance right?
Are the forms of nutrients and the doses going to meet the requirements of your horses?
To help answer these questions, consider the following:
Completeness
Metabolism is complex, requiring a broad range of essential nutrients. You can’t just feed two or three of them and hope to support performance, recovery, health, and metabolism. A lot of one nutrient doesn’t make up for deficiencies in another. If you ran out of food in your house and tried to just live on a big bag of salt, you wouldn’t last long. It is, therefore, important to consider if the supplement you are evaluating is complete enough to meet the complex requirements of equine physiology.
Balance
The balance between nutrients is equally important. Some nutrients are required for the uptake and function of other nutrients. (These supportive and cooperative nutrients are called co-factors.) Too much or too little of one nutrient may result in deficiencies or toxicities of other nutrients. Imbalances, therefore, can have a negative impact on health, performance, and recovery. At a minimum, imbalances in a feed or supplement can cost you money and have no effect at all.
For example, vitamin C is required for the absorption of iron from the gut. Without it, iron passes straight through the gut and out in the manure. Vitamin E binds with iron and reduces its absorption, causing much of it to be wasted. So, for horses to use dietary iron effectively, it has to be given with Vitamin C and without Vitamin E.
Bioavailability
Bioavailability refers to how well nutrients are absorbed and used. While this is partly related to the composition and balance of nutrients in a product, this is also about the form each nutrient is provided in. Some forms are more easily absorbed and used by the body than others.
The trace element chromium, for example, exists in several different forms. The form of chromium found in a chrome bumper on a car is, as you can imagine, not very digestible at all. The more organic forms like chromium picolinate (for people) or those incorporated into yeasts (a form often found in daily feed supplements for horses) is very easily absorbed and then used by cells. Minerals including calcium, magnesium, iron, cobalt, copper, zinc, selenium, and manganese can all be provided in a variety of forms, each of which have differences in their bioavailability.
In general, inorganic forms of nutrients are less well used than organic forms, though that is not always a reliable rule. Zinc oxide is one of the more bioavailable forms of zinc, whereas zinc chelate forms a big molecule that can be too big to be well absorbed. In most cases, though, minerals provided as gluconates, lactates, and amino acid or protein complexes are well used.
When reading labels, you should note whether the amount of the ingredient or the amount of the active nutrient is listed. For instance, Iron Bioplex, in which iron is bound to amino acids, contains only about 10% iron. If a label says a product contains 400mg of iron per dose, that means that a dose contains about 4000mg of Iron Bioplex yielding 400mg of very well absorbed and used iron. If the label says a product contains 400mg of Iron Bioplex per dose, then it really only has 40mg of actual iron. Make sure that you check those details carefully when reading labels and comparing products.
Doses and Nutrient Requirements
Do the doses of nutrients meet science-backed nutrient requirements? Caution! This might require math before you can measure a supplement against published nutrient requirements.
Labels will include the quantity of each nutrient, but those might be listed per kilogram or per dose. They might be in milligrams (mg), grams (g), or kilograms (kg), pounds (lb), ounces (oz), parts per million (ppm), percentages, or in some cases, a combination of units. All of these must be converted to the same units as the published nutrient requirements, and all have to be calculated per dose. It sounds seriously confusing, and it can be, but it’s also vitally important. If math isn’t your thing, ask a nutritionist for help. You can look up “NRC requirements” yourself or ask your nutritionist or veterinarian for help with this, too. Many feed companies have in-house nutritionists, and this can be a good way to get help, for a minimal charge or even for free, if you don’t have your own nutritionist.
Here's a tip to help make things easier:
If labels are easy to understand, and you can tell, at a glance, what you are feeding your horse in a single dose, then the manufacturer probably believes their formulation will stand up to scrutiny. If you have to perform too many calculations to figure out what you are giving, there’s a fair chance that the formulation isn’t great.
In any case, take the time to do the math and make sure you are comparing apples to apples before picking a supplement to spend your money on.
Addressing Specific Conditions or Concerns
Once the ration is properly balanced and nutritional requirements are being met effectively, you might also wish to feed supplements designed to address specific health issues. Nutraceuticals fed for healthy joints and tendons, or as digestive aids are common examples, and nutritional elements (vitamins, minerals, and amino acids) are also marketed for specific concerns. For example, vitamin K1 may support the development of strong cannon bones; biotin is fed to horses on high grain diets to support healthy hooves; chromium is fed to support muscle cells; and a variety of nutrients are fed to relax highly strung horses or to support red blood cell production in anaemic horses.
If you are looking at extra supplements like these, there are a few important questions to ask.
What scientific evidence is there that these products are likely to be effective?
Are the doses provided the same as the doses that produced good results in studies?
If nutritional elements are to be fed, do the amounts meet NRC requirements and are the cofactors needed for their absorption and effect also provided?
What quality, safety, and security assurance does the manufacturer provide?
Quality, Safety, and Security
How do you know if the product you are looking at contains what is says it does; only a fraction of what it says it has; or way more than it is supposed to have? Even more alarmingly, how do you know it doesn’t contain contaminants that aren’t supposed to be there?
There was an interesting study presented at an American Associate of Equine Practitioners (AAEP) meeting several years ago, in which several nutraceuticals were tested and their actual contents were compared with label claims. Those products were found to contain anywhere between 10 and 200% of the active ingredients that they were supposed to have. That is potentially a huge problem! If a product has too little of an ingredient, it may not be effective and will be a waste of money, but if it has a lot more than it is supposed to have, it may make horses sick or return a positive drug test result. We have already talked about how only a little too much selenium can be toxic, but for some nutrients like cobalt, an essential trace-mineral, feeding too much will produce a positive drug test. Contamination of feed supplements with Naturally Occurring Prohibited Substances, like caffeine, can also produce a positive test.
So, how do you know if a product is manufactured safely and meets its label claims?
This information isn’t generally on the label, but it can be just as important as the label itself. To get it, you either have to know the company management personally and have confidence in their diligence and ethics; you might have to talk to the manufacturer and ask questions; you can look at their website to find a statement about quality management; or you can look for third-party certification of their quality management practices. GMP or ISO certification are good ones to watch for. If a company has either ISO or GMP certification, you can be sure that the supplements they produce will be safe, secure, and generally meet label claims.
If a manufacturer lacks certification, it doesn’t mean they aren’t doing a fabulous job of quality management. They might have a written statement about their commitment to quality management or you might have to ask some questions to be sure. If at least some proportion of finished product undergoes analysis for common contaminants, the concentration of active ingredients, and microbial testing, it will likely be safe. If no testing is done, and the company doesn’t talk about product quality, safety, and security, you should be concerned.
Tip: Be sure to ask every rep that visits your stable about quality management as they will almost certainly be the most readily available source for this information. That is also a simple way to separate the wheat from the chaff. Any rep that can’t talk competently about their company’s quality management program, probably represents a company that doesn’t have one.
Feeding supplements can be necessary for adequately supporting horses, particularly during times of hard training, racing, competition, transport, illness, or stress. It is your responsibility to ensure the supplements you are feeding are necessary, complete, balanced, bioavailable, effective, and safe for health and drug testing. Get good value for money by avoiding under or over-supplementing. Hopefully I have helped you to make good choices, but remember, if in doubt – seek further advice from an equine nutritionist, veterinarian, or feed manufacturer.
Trust your gut - the importance of feeding the gut microbiome for health, performance & longevity
Article by Dr. Richard McCormick, M.V.B., Dip. Eq.Sc., M.R.C.V.S.
The science of equine nutrition is really quite simple – The horse is a flight animal and in the wild, needs to be able to escape from predators using a short burst of energy. Nutrition and subsequent ‘energy’ for survival is all provided by grass which has the required balance of vitamins, minerals, immune supportive nutrients and fibre to maintain a healthy gut microbiota and keep the horse in adequate health for reproduction. Proper functioning of the gastro-intestinal tract (GIT) in horses is dependent on a broad range of micro-organisms and more than half of the energy requirement for their survival comes from the microbial fermentation occurring in their enlarged caecum and colon (Chaucheyras-Durand et al 2022). The bacterial populations resident in the various compartments of the horses intestinal tract vary greatly (Costa et al 2015) and there is more DNA in the bacteria located in the gastro-intestinal tract than there is in the entire body. Because of this, having a healthy gut flora is critical to having a healthy immune system.
In modern times, our demands of horses for performance for our pleasure rather than their survival has led to their need for increased energy that cannot be provided from grass alone. Because of this, the intricacies of diet (in particular the consumption of starch, fibre and fat) has come under scrutiny. Equine feed manufacturers have looked for additional sources of starch, a carbohydrate and a natural component of grass that is ‘essential to provide energy, fibre and a sense of fullness’ (Seitz 2022). Today, most horses and rapidly growing foals are commonly fed diets with >50% of total ration by weight in the form of grain ‘concentrates’ and carbohydrates from oats, maize, soya, barley and wheat. These grain based feeds contain high concentrations of soluble, easily fermentable starches but can be deficient in certain minerals and vitamins so getting an optimally balanced feed ‘right’ is difficult.
Too much of a good thing
With advances in scientific knowledge, we now know that when a horse is exposed to surplus starch, the hydrogen ion concentration of their gut increases promoting the production and absorption of lactic acid, acetate and propionate through the activity of fermentation (Ralston 1994). The process is quick, with lactic acid entering the bloodstream within 3 hours of feeding and calcium subsequently being excreted in the urine. In order to combat this nutrient loss, the horses’ hormone system triggers the release of parathyroid hormone into the bloodstream, activating the release of stored calcium (to maintain optimal blood levels) but unfortunately causing bone demineralisation. Clinically, the horse experiences health consequences of varying degrees including digestive diseases (eg: gastric ulcers, diarrhoea, colic or colitis), muscle dysfunction (eg: rhabdomyolysis (known as ‘tying up’), defective bone mineralization (expressed as increased incidence of stress fractures and developmental orthopaedic diseases), systemic diseases (such as laminitis, equine metabolic syndrome and obesity (Chaucheyras-Durand et al 2022) as well as potential causes of fatigue.
The ideal equine diet
There is little equine focused research available on the benefits of individual nutrients (due to limited numbers in trials and their subsequent evaluation) of grain ‘concentrates’. But we do know that ingredient availability and quality is regularly influenced by market pressures.
The table (fig 1) below outlines the sugar, starch and fibre components of the various ingredients commonly found in horse feeds. The optimal grain for equine nutrition with its efficient energy source through lower starch content (relative to other grains) and its high level of soluble fibre (relative to other grains) are oats.
Oats are highly digestible and do not require heat treatment or processing prior to feeding (unlike all other grains). They are the only grain that is easily digested raw and the least likely to cause insulin spikes and blood sugar fluctuations. Unfortunately, oats are not a ‘complete’ nutrient source as they are high in phosphorous and low in calcium. For adequate bone and muscle development as well as proper blood formation, oats must be balanced with additional vitamins and minerals.
The healing power of omegas and short chain fatty acids
While grass provides optimal equine nutrition in its own right, the ‘curing process’ when making hay depletes the valuable omegas 3 and 6 intrinsic in grass. These ‘healing’ nutrients naturally protect the lining of the gastro-intestinal tract by increasing mucous production and alleviating ‘auto digestion’ (via hydrochloric acid). For horses, bacterial fermentation in the hind gut also results in the production of Short Chain Fatty Acids (SCFAs), namely acetic, proprionic and butyric acids. These SCFAs ‘cross talk’ with the gut immune system providing local immunity in the gut as well as protection of the respiratory system, the brain and other tissues against disease. In human medicine, it has been repeatedly established that a dysfunctional gut microbiome is associated with respiratory problems. This is evidenced by the fact that when gut disorders such as Irritable Bowel Syndrome (IBD) or Coeliac disease exist in humans, they are commonly associated with a higher incidence of respiratory infections and related asthmatic like conditions. Barragry (2024) explores the relationship (Fig 2) between gut microbiome and the immune system's ability to support health and combat disease in cattle. A scenario mirrored in the equine.
The stabled horse should be provided with SCFAs daily to support proper functioning gut microbiome. This critical dietary consideration should ideally be provided in the form of flaxseed which has the highest ratio of omegas 3 and 6 (in the ideal ratio 4:1) in the plant world and is most suitable for the equine herbivore.
The health benefits of flaxseed for both humans and equines has been recognised as early as 3,000 BC. Flaxseed was used for various medicinal purposes such as the treatment of gastric disorders, as a soothing balm for inflammation and as a laxative (Judd, 1995). Horsemen (who relied heavily on their equines) and trainers (who sought optimal performance from their charges through natural means) also used flaxseed as a way to supplement the diet with omega-3’s and fibre to produce high quality proteins. Now, thirteen centuries later, we have research to substantiate the knowledge of our ancestors. The renowned German researcher of ‘fats’ and pioneer in human nutrition, Dr. Joanna Budwig, as early as the 1950’s reported that “the absence of highly unsaturated fatty acids causes many vital functions to weaken". Dr. Budwig’s life’s work focused on the dietary ‘imbalance’ between omega-3 and omega-6 fatty acids in humans has been a cornerstone to the exploration of the role of inflammation and the development of many diseases of the coronary, respiratory, metabolic and immune system.
The small seed of the flax plant is also an excellent source of high-quality protein (exceeding that of soybeans and fish oils) and potassium (a mineral that’s important for cell and muscle function). But, the true power of flaxseed lies in three key components:
Omega-3 essential fatty acids – Also known as "good" fats, omegas enhance the oxygen usage of cells and in combination with alpha-linolenic acid (ALA) are anti-inflammatory in their effect within the body.
Lignans – Flaxseed contains 750 - 800 times more lignans than other plant foods (McCann 2007, Yan 2014). Lignans are a group of compounds with antioxidant properties which also contain plant oestrogen. Lignans are linked to a reduced risk of developing osteoporosis, heart disease and cancer.
Fibre - Flaxseed contains both the soluble and insoluble types of fibre essential for maintaining ‘gut’ health.
In equines, adding flaxseed to the diet has the immediate benefits of a shiny, healthy coat and fewer skin allergies. Consistent use of flaxseed has multiple long term benefits including strong hoof quality, improved joint health, reduced muscle soreness, faster healing of ulcers (Sonali et al 2008) and significantly impacts inflammation associated with chronic skin conditions (commonly known as ‘sweet itch’). In breeding stock, increased Omega-3 levels in mares’ milk leads to boosted immunity in foals with higher stallion fertility and improved conception rates in broodmares documented (Holmes, 2015).
How diet can influence performance
It is easy to think that ‘providing more is better’ when it comes to using nutrition to support performance. But having excess levels of essential vitamins and minerals being processed by the horses’ sensitive gut has a direct impact on their behaviour and willingness to perform. Today, we have greater ‘choice’ at the feed store with a broad range of commercial feeding offerings available including mixes, mashes and supplements but the discerning horse owner can be forgiven for being overwhelmed by the range of diet options for every ailment and stage of life.
In modern times, despite advances in nutrition offerings, we have seen a falloff in performance (Fig 3). During the late 1960s, the U.S. Jockey Club stats noted that racehorses averaged 12 starts per year – a far cry from today's horses racing in the U.S. where the average of 3 ‘starts’ was highlighted by leading US Trainers in 2020 (www.ownerview.com). Unfortunately, this is not just a U.S. based problem, but a phenomenon noted worldwide.
The first equine pelleted feed was formulated in the US by the Cistercian monks in Gethsemani, Kentucky in 1957. Prior to this, all horses were fed ‘straights’ (primarily oats as their energy source and flaxseed as their protein source). My own understanding of the link between modern feeding practices and compromised performance since the 1960s has been curated off an understanding of “what was different” then, as well as a career of observations, clinical practice and scientific review. Fact is, the equine diet of the 1960s was lower in starch and high in fibre. It consisted of oats, minerals, and flaxseed as the “norm”. Hay was the preferred forage (Fig 4).
Today, soya (with one fifth of the omega 3 content of flaxseed) has practically replaced flaxseed as the protein source in equine nutrition. This small change has seen a significant drop in omega-3 and 6 (needed for prostaglandins) in the diet with consequential gastro-intestinal and joint issues. Other dietary changes include those recommended by the National Research Council (NRC) in 1978, who suggested doubling the recommended calcium levels for horses with a subsequent increase in levels of Osteochondrosis (OCD) and Osteopetrosis in the equine population (Krook and Maylin, 1989). Additional moisture in the diet too has led to excess mould formation in convenience feeds and with severe exposure causes liver damage (Buckley et al 2007). Stabled racehorses today mostly lack the nutritional protection afforded a previous generation of horses. The impact has been noted clinically in the widespread increase in equine gastric issues and as stated by J.E. Anthony “Racing fans are missing about half of what they once enjoyed in racing.”
The role of the gut bacteria in the prevention of disease
The gut microbiome begins populating and diversifying from the moment of birth. Though ‘sterile’ in utero, gut derived DNA immediately drives immune health with exposure to nutrition. Recent research suggests that the gut microbiome can be stimulated by using proven probiotics with a track record in enhancing gut health (Barragry 2024). But it is the protective power of SCFAs to allow ‘cross talk’ between the lungs and the gut microbiome that is critical to supporting horses through their lifespan.
Nutrition using grain ‘concentrates’ is currently at approximately 99% saturation in today’s equine population so a return to feeding ‘straights’ is a swim against the tide of modernity. But, knowing the influence of nutrition on health, performance and longevity it falls on horse owners to be mindful of the consequential impacts such convenience feeds have on the gut microbiome and immune system. Random supplementation and high starch feeds are leading to dietary health issues such as gastric ulcers, hyperinsulinemia and hyperlipaemia (obesity) as well as increased risk of laminitis . So trust your gut and keep it simple – a diet of oats, flaxseed, a multi-vitamin balancer and ad lib hay will not only meet your horses’ energy needs but will keep them happy and healthy too.
REFERENCES
Barragry. TB (2024) WEB https://www.veterinaryirelandjournal.com/focus/254-alternatives-to-antibiotics-probiotics-the-gut-microbiome-and-immunity
Buckley T, Creighton A, Fogarty (2007) U. Analysis of Canadian and Irish forage, oats and commercially available equine concentrate feed for pathogenic fungi and mycotoxins. Ir Vet J. 2007 Apr 1;60(4):231-6. doi: 10.1186/2046-0481-60-4-231. PMID: 21851693; PMCID: PMC3113828.
Budwig, Dr. J (1903-2008) WEB https://www.budwig-stiftung.de/en/dr-johanna-budwig/her-research.html
Chaucheyras-Durand F, Sacy A, Karges K, Apper E (2022). Gastro-Intestinal Microbiota in Equines and Its Role in Health and Disease: The Black Box Opens. Microorganisms. 2022 Dec 19;10(12):2517. doi: 10.3390/microorganisms10122517. PMID: 36557769; PMCID: PMC9783266. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9783266/
Holmes, R (2015) Feeding for stallion fertility. WEB
https://www.theirishfield.ie/feeding-for-stallion-fertility-172113/
Judd A (1995) Flax - Some historical considerations. Flaxseed and Human Nutrition, S C Cunnane, L U Thompson. AOCS Press, Champaign, IL 1995; 1–10 [Google Scholar]
Martinac, P (2018) What are the benefits of flaxseed lignans? WEB https://healthyeating.sfgate.com/benefits-flaxseed-lignans-8277.html
National Research Council. 1989. Nutrient Requirements of Horses. Washington D.C.: National Academy Press.
Ralston, S VMD, PhD, ACVN (1994) The effect of diet on acid-base status and mineral excretion in horses in the Journal of Equine Practice. Vol 16 No. 7. Dept of Animal Science, Rutgers University, New Brunswick, NJ 08903
Seitz, A (2022) What to know about starch_Medically reviewed by Seitz, A - MS, RD, LDN, Nutrition — WEB https://www.medicalnewstoday.com/articles/what-is-starch#benefits
Sonali Joshi, Sagar Mandawgade, Vinam Mehta and Sadhana Sathaye (2008) Antiulcer Effect of Mammalian Lignan Precursors from Flaxseed, Pharmaceutical Biology, 46:5, 329-332, DOI: 10.1080/13880200801887732
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.
Nutrition and the new science of the "Gut-Brain connection"
Article by Scott Anderson
Trainers are always looking to gain an edge in performance. But what about their mental state? Are they jittery, distracted or disinterested? No matter how strong the horses, their heads must be in the game to succeed.
Surprisingly, much of that mental attitude is driven by gut health, which in turn depends on the collection of microbes that live there: the microbiota. In a horse, the microbiota is a tightly packed community of about 100 trillion microbes, composed of bacteria, archaea, fungi and protozoa. It colonises the entire GI tract but is largely concentrated in the hindgut, where it works to ferment the prebiotic fibre in forage. The microbial fermentation of fibre into fatty acids produces 70% of the animal’s energy requirements and without it, the horse couldn’t get sufficient energy from simple forage. Intriguingly, byproducts of that fermentation can affect the brain.
It is easy to be sceptical about this gut-brain connection, but over the last decade, research has made it clear that gut microbes have an outsized influence on mood and behaviour. Microbes that improve mental state are called psychobiotics, and they may completely change the way you train and manage your horses. A horse’s health – and consequently its performance – starts in the gut.
Inflammation
When the microbiota is unbalanced by stress, diet or sickness, it is said to be dysbiotic. It loses diversity, and a handful of bacterial species compete for domination. Without the pushback of a diverse population, even beneficial bacteria can become pathogenic. Surprisingly, that can affect the brain. Multiple studies in various animal models have shown that transmitting faecal matter from one animal to another also transmits their mood. This demonstrates that a dysbiotic microbiota can reliably cause mental issues including anxiety and depression, thereby affecting performance.
An important function of the microbiota is to fight off pathogens by outcompeting, starving or killing them. However, a dysbiotic microbiota is less diligent and may permit pathogens to damage the gut lining. A degraded gut lining can leak, allowing bacteria and toxins into the bloodstream. The heart then unwittingly pumps them to every organ in the body, including the brain. This makes the gut the primary source of infection in the body, which explains why 80% of the immune system is located around the intestines. Over time, a leaky gut can lead to chronic systemic inflammation, which weakens the blood-brain barrier and interferes with memory, cognition and mood.
Inflammation is a major component of the gut-brain connection, but not the only one.
Neurotransmitters and hormones
Horses and humans use neurotransmitters to communicate between nerve cells. Brains and their attendant nerve bundles constitute a sophisticated network, which makes it somewhat alarming that microbes also produce neurotransmitters. Microbes use neurotransmitters to converse with each other, but also to converse with their host. The entire gut is enmeshed in nerve cells that are gathered up into the vagus nerve that travels to the brain. Microbial neurotransmitters including serotonin and dopamine thus allow certain microbes to communicate directly with the brain via the vagus nerve. We know this happens with specific bacteria, including Lactobacillus species, because when the vagus is severed, their psychobiotic effects disappear.
As well as neurotransmitters, hormones are involved in gut-brain communications. The hypothalamus-pituitary-adrenal (HPA) axis controls the stress response in animals. The hypothalamus is located low in the brain and responds to stressors – such as a lurking predator – by producing hormones that stimulate the neighbouring pituitary, which then triggers the adrenal gland to produce cortisol, the stress hormone. Cortisol acts as a threat warning and causes the horse to ramp up glucose production, supplying the energy needed to escape a predator. This is the same hormonal circuit that trainers exploit for racing.
The HPA axis produces cortisol in response to stress. Cortisol inhibits the immune system, which in combination with a leaky gut allows pathogens to enter the bloodstream. Susequent systemic inflammation and vagal feedback lead to stereotypies.
The production of these hormones redirects energy to the heart, lungs and muscles at the expense of the immune system. From an evolutionary point of view, the tradeoff makes sense: first escape the predator and deal with infections later. After the danger has passed, cortisol causes the HPA to return to normal – the calm after the storm.
However, continued stress disrupts that cycle, causing anxiety and diminishing the brain’s ability to store memories. This can dramatically interfere with training. Stress can also induce the release of norepinephrine, which promotes the growth of pathogenic bacteria including Campylobacter jejuni, Listeria, Helicobacter pylori, and Salmonella. Prolonged high cortisol levels can increase gut leakiness, potentially leading to infection and further compounding the situation. In the long term, continued stress leads to systemic inflammation, which is a precursor to problematic behaviours.
Short-chain fatty acids
When microbes consume proteins and fibre, they break them down into their constituent molecules, such as amino acids, fatty acids and sugars. These are the metabolites of the microbes. As well as neurotransmitters and hormones, the gut-brain conversation is mediated by metabolites like butyrate, an important short-chain fatty acid which plays multiple roles in the body.
In the gut, butyrate serves as a preferred nutrient for the cell lining. It encourages the differentiation of stem cells to replenish gut cells that are routinely sloughed off or damaged. It plays an important role in the production of mucus – an essential part of gut protection – which coats the gut from mouth to anus. In the muscles, butyrate boosts the growth of skeletal muscle, crucial to athletic performance, as well as inducing the production of glucose, the primary muscle fuel. One-quarter of systemic glucose is driven by butyrate. In its gut-brain role, butyrate passes through the blood-brain barrier, where it nourishes and enhances the growth of new brain cells.
These factors make butyrate a star player in the gut-brain connection. They also highlight the benefits of prebiotic fibre, especially when high-energy, low-fibre feeds are provided.
Starting a microbiota
We’ve explored the major pathways of the gut-brain connection: inflammation, neurotransmitters, hormones and fatty acids. Some of these pathways are at odds with each other. How does such a complicated system come together?
As mentioned, the microbiota is an animal’s first line of defence against pathogens, attacking and killing them often before the immune system is even aware of them. That means a healthy microbiota is an essential part of the immune system. However, the immune system is designed to attack foreign cells, which includes bacteria. For the microbiota to survive, the immune system must therefore learn to accept beneficial microbes. This lesson in tolerance needs to take place early in the foal’s development, or its immune system may forever fight its microbiota.
There are multiple ways nature ensures that foals get a good start on a microbiota that can peacefully coexist with the immune system. The first contribution to a protective microbiota comes from vaginal secretions that coat the foal during birth. After birth, microbes are included in the mare’s milk. These microbes are specially curated from the mare’s gut and transported to the milk glands by the lymphatic system. Mare’s milk also includes immune factors including immunoglobulins that help the foal to distinguish between microbial friends and foes. An additional way to enhance the microbiota is through coprophagia, the consumption of manure. Far from an aberration, foals eat their mother’s manure to buttress their microbiota.
Microbes affect the growth and shape of neurons in various brain sites as the foal develops – a remarkable illustration of the importance of a healthy early gut microbiota.
The cooperation between the immune system and the microbiota is inevitably complex. Certain commensal bacteria, including Clostridiales and Verrucomicrobia, may be able to pacify the immune system, thus inhibiting inflammation. This is a case where microbes manage the immune system, not the other way around. These convoluted immune-microbial interactions affect the mental state – and consequently the behaviour – of the horse, starting at birth.
Stereotypies
A 2020 study of 185 performance horses conducted by French researchers Léa Lansade and Núria Mach found that the microbiota, via the gut-brain connection, is more important to performance than genetics. They found that microbial differences contributed significantly to behavioural traits, both good and bad. A diversified and resilient microbiota can help horses better handle stressors including stalling, training, and trailering. A weakened or dysbiotic microbiota contributes to bad behaviours (stereotypies) and poor performance.
The horses in this study were all carefully managed performance horses, yet the rates of stereotypies were surprisingly high. A kind of anxiety called hypervigilance was observed in three-quarters of the horses, and almost half displayed aggressive behaviour like kicking or biting.
The study found that oral stereotypies like biting and cribbing were positively correlated with Acinetobacter and Solibacillus bacteria and negatively correlated with Cellulosilyticum and Terrisporobacter. Aggressive behaviour was positively correlated with Pseudomonas and negatively correlated with Anaeroplasma.
Some of these behaviours can be corrected by certain Lactobacillus and Bacteroides species, making them psychobiotics. That these personality traits are correlated to gut microbes is truly remarkable.
Intriguingly, the breed of a horse has very little impact on the makeup of its microbiota. Instead, the main contributor to the composition of the microbiota is diet. Feeding and supplements are thus key drivers of the horse’s mental state and performance.
The gut-brain connection and training
How might the gut-brain connection affect your training practices? Here are some of the unexpected areas where the gut affects the brain and vice-versa:
High-energy feed. Horses evolved to subsist on low-energy, high-fibre forage and thus have the appropriate gut microbes to deal with it. A high-energy diet is absorbed quickly in the gut and can lead to a bloom in lactic acid-producing bacteria, which can negatively impact the colonic microbiota. High-energy feeds are designed to improve athletic output, but over time, too much grain can make a horse antisocial, anxious and easily spooked. This can damage performance—the very thing it is trying to enhance. Supplementary prebiotics may help to rebalance the microbiota on a high-starch regimen.
Changing feed regimens quickly. When you change feed, certain microbes will benefit, and others will suffer. If you do this too quickly, the microbiota can become unbalanced or dysbiotic. Slowly introducing new feeds helps to prevent overgrowth and allows a balanced collection of microbes to acclimate to a new regimen.
Stress. Training, travelling and racing all contribute to stress in the horse. A balanced microbiota is resilient and can tolerate moderate amounts of stress. However, excessive stress can lead, via the HPA axis, to a leaky gut. Over time, it can result in systemic inflammation, stereotypies and poor performance.
Overuse of antibiotics. Antibiotics are lifesavers but are not without side effects. Oral antibiotics can kill beneficial gut microbes. This can lead to diarrhoea, adversely affecting performance. The effects of antibiotics on the microbiota can last for weeks and may contribute to depression and anxiety.
Exercise and training. Exercise has a beneficial effect on the gut microbiota, up to a point. But too much exercise can promote gut permeability and inflammation, partly due to a lack of blood flow to the gut and consequent leakiness of the intestinal lining. Thus, overtraining can lead to depression and reduced performance.
Knowing how training affects the gut and how the gut affects the brain can improve outcomes. With a proper diet including sufficient prebiotic fibre to optimise microbiota health, a poor doer can be turned into a model athlete.
References
Mach, Núria, Alice Ruet, Allison Clark, David Bars-Cortina, Yuliaxis Ramayo-Caldas, Elisa Crisci, Samuel Pennarun, et al. “Priming for Welfare: Gut Microbiota Is Associated with Equitation Conditions and Behavior in Horse Athletes.” Scientific Reports 10, no. 1 (May 20, 2020): 8311.
Bulmer, Louise S., Jo-Anne Murray, Neil M. Burns, Anna Garber, Francoise Wemelsfelder, Neil R. McEwan, and Peter M. Hastie. “High-Starch Diets Alter Equine Faecal Microbiota and Increase Behavioural Reactivity.” Scientific Reports 9, no. 1 (December 9, 2019): 18621. https://doi.org/10.1038/s41598-019-54039-8.
Lindenberg, F., L. Krych, W. Kot, J. Fielden, H. Frøkiær, G. van Galen, D. S. Nielsen, and A. K. Hansen. “Development of the Equine Gut Microbiota.” Scientific Reports 9, no. 1 (October 8, 2019): 14427.
Lindenberg, F., L. Krych, J. Fielden, W. Kot, H. Frøkiær, G. van Galen, D. S. Nielsen, and A. K. Hansen. “Expression of Immune Regulatory Genes Correlate with the Abundance of Specific Clostridiales and Verrucomicrobia Species in the Equine Ileum and Cecum.” Scientific Reports 9, no. 1 (September 3, 2019): 12674.
Daniels, S. P., J. Leng, J. R. Swann, and C. J. Proudman. “Bugs and Drugs: A Systems Biology Approach to Characterising the Effect of Moxidectin on the Horse’s Faecal Microbiome.” Animal Microbiome 2, no. 1 (October 14, 2020): 38.