Trust Your Gut – the importance of nutrition for health, performance and 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  fiber 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, fiber 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, fiber 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, diarrhea, colic or colitis), muscle dysfunction (eg: rhabdomyolysis (known as ‘tying up’), defective bone mineralization (expressed as increased incidence of stress fractures and developmental orthopedic 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 fiber 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 fiber (relative to other grains) are oats.

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 recognized 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 fiber 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 estrogen. Lignans are linked to a reduced risk of developing osteoporosis, heart disease and cancer.

Fiber - Flaxseed contains both the soluble and insoluble types of fiber 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 behavior 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 compromized 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 fiber. 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 life span. 

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

Probiotics – The key to a well-balanced equine gut

Article 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.  

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.

Figure 1: Factors that can lead to gut dysbiosis

What exactly is a probiotic?

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.