The Native Equine Diet: Exploring the Ancestral Forage of Horses (Part 2)

February 7, 2024

By Sarah Griffiths, DCH

The old sentiment that horses eat hay is not entirely accurate. We all know that forage quality is an important aspect of equine nutrition but today’s methods for analyzing the meaning of a “healthy diet”  for equines has gotten…. confused. An oversimplification has manifested in modern day equine nutrition programs resulting in some serious consequences. We’re using outdated science as reference points and it’s costing horses their health. To understand the trajectory of common equine diseases like gastric ulcers and colic, we need explore other fields of science including biological evolution, ecology, pathology and epigenetics.

Today’s article is the second piece in a series of writings on why we need change in the field of modern equine nutrition. If you missed the first entry, please check out Part 1: Are Modern Diet Recommendations Failing Horses? In part 1, I shared some disturbing equine health statistics from the NIH on colic, ulcers and insulin resistance. These numbers are unacceptable and should not be considered normal. Given the prevalence of these (largely) nutritionally-created diseases, we need some new tools to help horses. Conventional treatments are not contributing to long term solutions for these diseases. Instead, horse owners are being given short-acting, immune-suppressive and expensive medications that provide temporary relief without addressing the underlying cause. If you’ve been on this gut-health hamster wheel with your horse, you’re not alone.

The most shocking statistics I uncovered in my exploration of equine disease prevalence were that conventionally kept horses have ulcers at a rate of 70-90% whereas in an abattoir study done in the UK, the ulcer rate of feral horses is approximately 30%. (1) (2) (3) Since there is no research into colic incidents within wild horse populations, I was unable to compare it with modern horse statistics, however, colic remains the number one cause of death in captive horses with ulcers being a major contributing factor in recurrent colic cases. (4) Insulin resistance is prevalent amongst aging horses and is the major contributing factor in the development of laminitis, a painful disease that’s often fatal at some stage of its development.

With so many horses struggling with life-threatening chronic conditions, it makes no sense to assume that this is normal. We cannot keep going in the same way and expect different results. This is the definition of insanity. It’s important to recognize that these pathologies have well-researched dietary causes. As you’ll read below, there are some glaring differences in the dietary intake of wild horses versus their domestic counterparts. These differences illuminate clues about where we can improve in modern equine nutrition protocols.

What and how do wild horses eat?

In their natural environment, horses eat a wide variety of plants in various seasonal stages of maturity. When we compare the native diet of horses to modern feeding practices, it’s easier to understand where the failures are occurring in supporting equine nutritional needs.

Wild horses eat in seasonal rotation and consume very little in the way of immature green grass, except in the spring. My research revealed that feral horses forage for dozens of additional plant species that are not in the grass (grammanoid) family. Their diet does not traditionally consist of perfectly timed cuts of the same 5 grass species harvested in terms of their period of highest “digestibility.” This is how modern equine hay production is managed. Besides the spring season, horses do not feed on young grasses, nor do they stick to one forage all year round. Most of the year, they are consuming mature plants that are much higher in fiber than what’s found in hays being fed to modern horses. This fact is a missing link to discovering the truth about what we should be feeding.

According to several research studies that I discovered on feral horse populations, wild horses eat a variety of grasses, shrubs, leaves, flowers, bark, herbs and are proficient in finding mineral deposits. (5) (6) (7) They also forage for different plants and different parts of those plants during the changing seasons. (8) (9) (10) (11) Native equine foraging skills are genetically acquired instincts that have developed in relation to their environment and their evolved physiology. Plant foraging has been almost completely stifled in modern equine management practices. A field full of green grass doesn’t count!

I wanted to understand the full spectrum of equine forage selection and decided to dive in to the research. After several months of research and calculations, I came up with the following averages in the variety of the feral horse diet. It looks something like this:

Species of grasses: 16 – 68.77% of the total diet.

Species of shrubs and trees: 7 – 11.99% of the total diet

Species of forbes (nutritive herbs): 19  – 19.24% of the total diet.

Soil and mineral deposits: Approximately 4% of the total diet.

A key note about this data is the is variety in their native forage. These studies indicate a minimum of 42 plant species in the diet of feral horses. Only 16 species were grasses compared to 26 other non-grass species. I also discovered that as seasonal cycles occur, horses adjust their foraging behaviours in relation to the nutritional content and availability of plants during each season. I, myself, have witnessed this in domestic horses that are given the chance to forage in natural environments. You can follow along with my documentation of this on my social media platforms. (@theanimalsynergist)

What does this all mean for modern horses? It means that they dynamically and synergistically adapt to their environment, taking in different nutrients at different times of the year. They also forage for a diverse number of highly so-called “indigestible” fiber sources (we’ll explore the importance of this later). This is how they complete their nutritional profile. They don’t eat one forage all year round. And they didn’t start doing this yesterday – they spent millions of years specializing their forage selections.

The most important macronutrient for horses is fiber which is a type of complex carbohydrate. Of course, horses also need protein and fat but in studying their ancestral diet, protein and fat are quite minimal in comparison to complex carbohydrate. Their physiology and anatomy also reflect this fact. When we look at the fiber sources that horses naturally consume, it’s highly variable and changes with the seasons. Conventionally kept horses that are not given the opportunity to forage are often fed only one or two types of hay all year round with the addition of a synthetic vitamin and mineral ration. I refer to this way of feeding as a “mono-diet” or “mono-forage” program. This method of feeding is not accurate in relation to their native diet. We’ll get into why mono-diets are, arguably, a dangerous way to feed horses in my next article regarding equine gut health and microbiome status.

What is the purpose of consuming variable forage and fiber?

Why do wild horses select the plants that they do and why do they have such a different prognosis when it comes to the development of gastric ulcer formation? I believe the answers to these questions lie in their physiological ancestry. Science acknowledges this statement. My hypothesis is that the prevalence of gastro-intestinal and metabolic disease is a natural progression of the unmet environmental needs of the modern horse. Here’s why:

The horse, in digestive terms, is a hind-gut fermenter or cecal fermenter. This system evolved in horses over 35 million years ago – a significant length of time in relativity to how long they have been domesticated – approximately 6000 years. Physiological and anatomical changes do not occur in 6000 years. This is not my opinion. It is scientific fact. A study published in 2011 and conducted at Oregon State University by Zoologist Josef Uyeda concluded that long-lasting physiological changes take at least one million years to occur. On the other hand, environmental stress can also illicit significant short term genetic mutations – in the form of disease processes. (12) Horses did not evolve cecal digestion overnight and it was not an accident. It was an intelligently designed evolutionary adaptation that mirrored the environmental conditions they faced millions of years ago. We can’t suddenly and drastically modify their diet without consequence.

Since industrialized equine feeding methods have only existed for about 150 years, we can conclude that it’s not possible for horses to have “evolved” to consume an industrialized mono-diet. Referring to human research on what is accepted as a healthy diet, we can also conclude that complex mammalian species need a variety of species-specific whole foods to truly thrive. Scientists, governments and the United Nations all conclude that the definition of a healthy diet is varied, fresh and free of ultra-processed foods. (13) (14) (15)

If you’ve been told that all your horse needs is water, hay and industrialized feed, throw this belief out the window. It’s nonsense and also completely unscientific. The difference between industrialized feed science and actual nutrition science is vast. Zooming out into the fields of basic biology, genetic evolution, epigenetics, equine veterinary pathology and adding a little bit of common sense, it becomes impossible to comprehend continuing in the current fashion when it comes to feeding horses. During this article series, you’ll be able to fully appreciate why I’m so adamant about changing the paradigm. Horses deserve better…

I use a method of triangulation to study the current scientific understanding of modern gastrointestinal pathologies with genetically-acquired equine physiological processes and current feeding practices. These pieces are vital in solving the so-called “mysteries” of modern equine disease origins. Equine biology is a mirror of their genetic evolution. And so is their pathology. We can’t ignore this and expect to see them thriving.

The unfortunate route that modern equine nutritional “science” has taken involves the study of how to provide minimum requirements necessary for avoiding nutritional deficiency. This is done using the most affordable and convenient feed options possible – ingredients that can be utilized from industry, not from nature. Industrialized nutrition logic always reminds me of the story of Frankenstein where we learned that cutting up the pieces of a subject based only on the information that we have deemed important or known does not equate to an accurate reconstruction of what’s true. Sure, it’s scientifically true that you can get the math right but does that equate to biological health? Modern equine disease statistics suggest the answer is no.

Feeding ultra-processed feed, synthetic supplements and conventionally farmed hay sources has very little to do with equine health. It’s mostly a practice in human convenience. And don’t be fooled into thinking that the more you pay for a supplement or a feed, the better care you’re giving your horse. Cost in relativity to branding and marketing is just as competitive as in the equine nutrition space as it is in the fashion industry. We can’t allow fancy marketing to blind us from the realities of how sick modern horses are.

I encourage you to review the scientific references below to fully understand the great disservice that conventional diets are doing for horses. It will give you a zoomed out perspective on how far we’ve strayed from what horses really need. It also sets us up to discuss the next sections of this article series: equine gut microbiology and common gut pathologies.

In next week’s article, we’re taking a deep dive into the ancestry and evolutionary development of the equine digestive system. We’ll discover the reason why horses evolved their hind-gut digestion process and why it’s imperative to use multiple fields of science to understand how to feed horses correctly and prevent digestive illness.


  1. Equine Sports Medicine and Surgery – Equine Gastric Ulcer: A Review – Nanna Luthersson, Jenifer A. Nadeau (2013)
  2. Journal of Equine Veterinary Science – Results of a large-scale necroscopic study of equine colonic ulcers – Pellegrini (2005)
  3. BEVA Equine Veterinary Education: Comparison of the prevalence of gastric ulceration in feral horses and domesticated horses in the UK, 2015
  4. Journal of the American Veterinary Association: Gastric Ulceration in Horses: 91 cases (1987-1990)
  5. Rangeland and Ecology Management: Comparison of methods to examine diet of feral horses from non-invasively collected fecal  samples, 2019
  6. Applied Animal Behaviour Science: Geophagia in horses: A short note on 13 cases, 2001
  7. Animals: Ingestion of soil by grazing sport horses, 2021
  8. University of Southern Queensland: The ecology of feral horses in central Australia, 1991
  9. Journal of Range Development: Foods of free-roaming horses in Southern New Nexico, 1976
  10. Journal of Range Management: Horses and cattle grazing on the Wyoming Red Desert, 3: 1984
  11. Journal of Range Management: Habitat selection patterns of feral horses in South Central Wyoming, 1997
  12. Environmental Health Perspectives: Epigenetics: The Science of Change, 2006
  13. Canada’s Food Guide, 2024
  14. Brazilian Food Guide, 2015
  15. Food and Agriculture Organization of the United Nations: Ultra-processed foods, diet quality and health using the NOVA classification system, 2019