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The question of whether horses need continuous access to hay or if feeding hay in meals is sufficient is a common query among horse owners. Observing a plump pony that seems to expand like yeast when fed hay continuously might lead one to believe that weight management can be achieved through simple rationing. The idea is that if a horse consumes fewer calories, it will either maintain its weight or even shed some pounds. This approach seems to work for us humans if we stick to disciplined eating habits. But here’s the catch: we often transfer our habits and needs to horses, neglecting the fact that horses are fundamentally different in several aspects due to their evolution.

Inferring from humans to horses?

Humans tend to project their own behaviours onto their horses. If we feel cold, we assume our horses need blankets. If we eat three meals a day, we might think horses should also have regular meal times. However, we overlook the fact that horses have evolved with distinct physiological and dietary requirements. Evolution has shaped horses in ways that differ greatly from humans. For instance, horses can run with remarkable speed and endurance, require less sleep, and possess digestive systems that fundamentally diverge from ours. Humans are classified as “omnivores,” akin to pigs. Over time, our bodies have adapted to extract nutrients and energy primarily in the small intestine, driven by a diet that includes animal products. Animal-derived foods like meat and eggs are energy-dense, contributing to the development of our large, powerful brains. Because of the concentrated energy content of our diet, we need relatively small quantities to meet our nutritional needs. This has shaped humans into “meal eaters,” with breaks between energy-rich meals, aligned with our body’s digestive rhythm. Because if we eat our rich food all day long, what happens is what can be observed in many western countries: fatty degeneration and corresponding diseases occur. Therefore, it is good and sensible for people to have longer breaks between energy-rich meals; our body is set up for this and it also needs them. We have the longest break at night because humans – comparable to predators – need a long, continuous sleep phase to regenerate.

Horses are adapted to a completely different diet

Contrastingly, horses’ evolutionary background places them in an entirely different dietary and lifestyle context. They are herbivores and not adapted to high-energy and nutrient-dense diets like humans. While humans might pluck and consume only the berries from a bush (high in sugar, low in fibre), horses consume the entire bush (low in sugar, high in fibre). Horses have evolved to thrive in environments where many other species struggle due to a scarcity of easily digestible food sources—such as steppes, semi-deserts, and tundras. Their vegan diet centres around converting even the leanest food sources, like plant fibres, into energy. Unlike us, plant fibres in horses are not simply discarded; they serve as the primary source of energy due to their availability throughout the year. This adaptation hinges on the presence of specialised cellulolytic microorganisms in the horse’s large intestine. These microorganisms break down plant fibres (cellulose) into energy, transforming what we perceive as indigestible fibre into a vital energy source. Consequently, horses boast a distinct composition of intestinal flora, enabling them to derive energy from plant fibres—a feat beyond our capabilities. Horses’ digestive systems are designed to continuously process plant materials, allowing for consistent energy intake throughout the day. Restricting this natural rhythm by feeding hay in meals can disrupt their digestive efficiency and result in unintended consequences such as weight gain, metabolic imbalances, and other health issues. Providing horses with access to hay throughout the day, mirroring their evolutionary dietary patterns, is essential for their overall well-being and optimal functioning of their digestive systems.

When examining the energy density of various molecules, it becomes evident that cellulose does possess energy, albeit in considerably smaller amounts when compared to other nutrients. For example, proteins offer 1.5 times the energy of sugars, while fats provide double the energy of sugars.

Cellulose is composed of complex chains of sugar molecules, making it challenging to digest. Consequently, it holds the lowest energy value when compared to protein or fat. Its complex structure renders it challenging for digestion, and as a result, not all of its energy content is accessible to the horse. Only the portion that remains after the microorganisms’ activity is available. As a result, horses must consume substantial quantities of feed to meet their energy requirements by the end of the day. However, the horse can only ingest these substantial amounts of feed if it eats virtually continuously.

Horses need 10-15 kg of lean hay per day

Both wild and healthy domestic horses exhibit comparable feeding behaviour and consume roughly the same amount of roughage. Horses typically require 2-3% of their body weight in lean hay to meet their energy needs. This equates to around 2-3 kg of hay per 100 kg of body weight, amounting to 10-15 kg per day for a 500 kg horse. The more nutrient-poor the hay, the more of it they will eat to meet their needs. This amount is not ingested in a single large meal, followed by a prolonged pause. Such a diet is what predators have, they strike prey, gorge their stomachs and then sleep for long periods to digest their energy-rich food until they get hungry again and go hunting again. Instead, horses consume their lean feed in small quantities throughout a 24-hour period, interspersed with numerous short breaks between eating.

© Adobe Stock / Valeri Vatel

The horse is not a meal eater

Unlike predators, the horse’s stomach is relatively small in relation to its body size and is not highly expandable. It lacks the capacity to intake large quantities at once. Additionally, when new food enters the horse’s stomach, a reflex triggers the passage of some food to the small intestine. As a result, the stomach remains consistently full but not overfilled. This differs from the stomach of a predator, which is familiar to those who have experienced dogs swiping food from the table. The horse’s stomach continuously produces hydrochloric acid, which is balanced in a natural diet through constant absorption and buffering by saliva. When a dog’s stomach empties, acid production ceases, whereas a horse’s stomach does not stop acid production even when it’s empty. This constant acid production is a leading contributor to the development of stomach ulcers in horses, as the acid erodes the stomach walls.

The horse’s stomach is adapted for continuous consumption, not intermittent meal eating. Feeding hay in meals disrupts this natural rhythm and encourages the development of painful stomach ulcers. Therefore, providing horses with continuous access to hay mirrors their evolutionary dietary patterns and supports the health of their digestive system.

The role of the small intestine in the horse’s digestion is secondary. Here, nutrients that are easily digestible by the small intestine, such as sugar, starch, fat, and protein, are broken down and extracted from the food. The horse can use these nutrients in small amounts for energy or as building blocks. However, in larger quantities, they can quickly become detrimental to the horse’s health, as its evolutionary history did not involve adapting to high levels of such nutrients.

So what are the most important nutrients and energy sources for us – the small intestine-digestible components – very quickly become harmful to horses and can lead to diseases such as insulin resistance, clinically manifest PSSM, kidney overload, fatty degeneration (EMS) and all the associated secondary diseases such as laminitis.

These elements must be present in the horse’s diet in limited quantities. The pivotal digestive region for horses is the large intestine and its complex microbiome.

Once the potentially harmful nutrients (sugar, starch, fats, and excessive protein) have been processed by the small intestine, the large intestine’s microorganisms begin to break down plant fibres. This process generates numerous nutrients that the horse can absorb and utilise, along with a significant amount of energy in the form of propionate, butyrate, or acetate.

A continuous supply of fibre material is needed

In order for the intestinal flora to work optimally, it needs a continuous supply of fibre material. If the large intestine becomes deprived of fibre, the microorganisms within begin to starve, causing detrimental consequences. As microorganisms perish, endotoxins are released, burdening the horse’s detoxification process, and potentially leading to laminitis. Additionally, the remaining microorganisms might consume the protective mucus layer of the intestinal lining due to their hunger, possibly triggering inflammation of the intestinal mucosa. This can manifest as symptoms like faecal water or a predisposition to colic.

Disorders of the large intestine environment are one of the main causes of most of the metabolic diseases we see in horses – from sweet itch to chronic coughing to laminitis

Supplying the intestinal flora with digestible plant fibre, especially cellulose, is of utmost importance. This clarifies why horses continually consume small amounts of hay without extended breaks from feeding.

Eating breaks cause stress

Last but not least, a lack of hay also has a negative effect on the horse’s psyche.

In the wild, a lack of food poses a life-threatening situation for horses, as weakened individuals become susceptible to predation. Consequently, domestic horses respond with heightened stress during periods of roughage scarcity. Research indicates that this stress heightens aggression within groups. Problematic behaviours like pawing, weaving, lip-chewing, and cribbing may also emerge or intensify when horses lack access to roughage. Beyond disrupting group dynamics, roughage deprivation also instigates physical stress.

This is because stress leads to the release of endogenous cortisol in horses, which not only suppresses the immune system and causes blood sugar levels to rise, but can also trigger Cushing’s symptoms in the long term.

The horse has adapted to a sparse diet

Over nearly 50 million years of evolution, horses have adjusted their digestive systems and metabolisms to subsist on a sparse diet of low-energy cellulose. Even when humans domesticated horses roughly 6,000 – 8,000 years ago, the equines were provided sustenance in the same manner as their wild counterparts for millennia. Agriculture introduced human-consumed crops like grains and turnips, but these were too precious to feed to horses. Horses could thrive on vegetation unfit for human consumption: grass, hay, leaves, straw, and shrubbery. It’s only within the last 150 years, due to industrialisation and modern agriculture, that energy-dense feedstuffs like grains have become part of equine diets. However, what evolution has crafted over 50 million years can’t be fully overturned in 150 years.

The equine digestive system still operates much like that of their wild ancestors.

Consequently, wild horses, such as the brumbies in Australia or abandoned mustangs in the US, manage well without a daily muesli ration, even within arid landscapes. Their digestive systems efficiently handle the modest nourishment found in the wild.

The horse’s digestive tract is adapted to a constant supply of nutrient-poor, cellulose-rich roughage.
© Adobe Stock/Eileen

Constant access to nutrient-poor, cellulose-rich roughage

This dilemma leads us directly to the issue with our overweight pony. Its digestive system has evolved to depend on a continuous supply of nutrient-poor, cellulose-rich roughage. However, the landscape of hay meadows has been drastically transformed by high-intensity agriculture over the last five decades. Pastures that once provided suitable roughage for horses have been replaced by vibrant green performance meadows filled with high-sugar grasses. While these grasses yield rapid gains in milk and meat production (often at the expense of livestock health), they are no longer appropriate for equine consumption. The more sugar in the hay, the more appealing it is to horses, as it tastes better to them. Regrettably, this high sugar content presents problems for horses, as their metabolic systems are not equipped to efficiently process large amounts of sugar. This dilemma forces us to acknowledge that the equine digestive tract fundamentally relies on a continuous roughage supply. Consequently, ensuring that horses have constant access to hay is imperative. Failing to provide this access can result in conditions like stomach ulcers or large intestine dysbiosis (abnormal fermentation), with severe consequences. However, if horses are permitted to freely consume high-sugar hay—especially if they are already accustomed to sugar due to daily concentrate feedings, generous carrot treats, and the occasional banana—there’s a risk of overindulgence in “sugar hay.” This excess consumption can overwhelm their metabolism, leading to potential issues such as obesity, insulin resistance, and subsequently laminitis.

This predicament prompts the question: What measures can be taken to address this challenge?

The initial step is always to eliminate all nutrient-rich (small intestine-digestible) feeds. While it might be satisfying for us to create elaborate meals for our horses and witness their enthusiastic consumption, even “grain-free mueslis” often contain added carrot pieces or oils for flavour, which are unsuitable for equine diets – especially for horses with weight or health concerns. Carrots, apples, bananas, and other fruits and vegetables should only be given sparingly and after careful consideration. In the case of horses with metabolic issues, it’s often better to avoid them altogether. Treats should be reduced to the minimum necessary amount. Once all fattening feeds have been minimised, the next step involves optimising hay feeding practices. Instead of fixed mealtimes, electronically controlled paddocks with enforced feeding breaks, or insufficient feeding spaces resulting in ongoing stress and conflicts, it’s crucial to ensure that all horses have unrestricted access to hay at all times. Straw is not an adequate substitute for hay; excessive consumption of straw can lead to constipation colic and should only be offered as a supplement to hay. The appropriate number of feeding spaces depends on the dynamics of the group. For well-harmonised groups, around 10% more feeding spaces than horses in the group are recommended. For groups with poorer compatibility or frequent changes, it’s advisable to provide twice as many feeding spaces. The speed at which horses consume their feed can be controlled through the use of slow feeder systems, with hay nets being a straightforward option. The mesh size should be selected according to the hay’s quality and the horses’ abilities. For example, coarse hay requires larger mesh sizes than fine hay. Heavier or clumsier horses need larger openings, while “hoover” ponies that devour their hay quickly should be provided with closely meshed nets, possibly mixed with straw.

Two horses eating hay
A species-appropriate diet for horses is only possible with continuous hay feeding. © Adobe Stock / Alexia Khruscheva


Only through continuous hay feeding, adjusted based on the hay’s nutrient content and the horses’ weight condition using slow feeder systems, can horses receive a species-appropriate diet. Any form of restricted access—whether through meal feeding, straw instead of hay, automatic hay feeders, and so on—induces significant stress that can lead to aggression, depression, stomach ulcers, immune system suppression, faulty fermentation in the large intestine, and subsequent ailments such as watery stools, diarrhoea, colic, insulin resistance, or laminitis.