Good fibers maintain a healthy gut bacterial population
When grazing, horses spend most of their day (12–17 hours) eating and foraging, and their digestive system is adapted to receiving small amounts of feed at short intervals. Naturally, a horse’s primary food source is fresh pasture grass, which is why the foundation of equine nutrition is appropriate forage. Adequate forage intake is essential for preventing diet-related diseases and behavioral disorders.
The horse’s digestive system is well adapted to breaking down fiber. Fibers are divided into soluble and insoluble fibers. Fiber has many functions in the body. It supports digestion, but also carries harmful substances out of the digestive tract and helps cleanse the intestines. The more diverse the fiber sources in the diet, the more chemically varied the fiber compounds are, and the better they can support different beneficial gut bacteria. Insoluble fiber increases fecal bulk and softens its structure. Soluble fibers form a gel in the gut and bind harmful substances, which then leave the body with the manure.
Grass contains about 20 percent fiber. Horses prefer grass that is about 15 cm long. As grass grows, it becomes more stemmy, which also increases its fiber content. However, there are significant individual differences in how horses digest fiber, and this can be a major factor in whether a horse tends to “keep weight on” easily. In addition to fiber, the horse’s digestive system digests sugar better than starch.
About 1.5 kg of forage per 100 kg of body weight
As a rule of thumb, feeding should provide about 1.5 kg of forage per 100 kg of body weight, meaning that a 500 kg horse should receive at least 7.5 kg of forage per day. If the forage is haylage with a dry matter content of 75 percent, about 9.5 kg of haylage should be fed to meet the forage requirement. Dried hay and herbs generally have low sugar and starch levels, and they help maintain a diverse bacterial population in the horse’s gut, which supports nutrient absorption and digestive function. The gut bacterial population—and its diversity—has a significant impact on the horse’s wellbeing and ability to utilize feed. For gut health, concentrates should be divided into as many meals as possible.
Equine digestion works with the help of enzymes and microbes
The purpose of the horse’s digestive system is to break down feed into a form that allows nutrients to be absorbed from the digestive tract and converted into energy for the body. In horses, digestion is carried out through digestive enzymes and intestinal microbes.
The most important part of the digestive tract for nutrient absorption is the small intestine, where most nutrients are absorbed. In the small intestine, enzymes digest the feed. The intestinal walls are constantly moving, carrying the feed forward. A sufficient amount of coarse feed material—i.e., fiber—promotes intestinal motility. Severe stress can slow intestinal movement, which can lead to constipation. For feed to move optimally through the small intestine, it should also contain plenty of fiber.
In the large intestine, the parts of the feed that the small intestine did not digest are broken down. The large intestine and its microorganisms play a major role in breaking down and utilizing fiber from forage and other fibrous feeds. Feeding must therefore ensure that the microorganisms in the large intestine receive enough fiber as a substrate, because disturbances in the large intestine become visible very quickly in the horse’s nutritional status. Hindgut bacteria also produce vitamins C and K as well as B vitamins.
Too little fiber increases the risk of digestive disturbances
A feed particle’s journey through the horse’s digestive system takes two to four days. The horse’s digestive system is unique and more prone to digestive disturbances than many other animals.
A diet containing only a small amount of fiber does not move normally through the horse’s digestive tract and can cause digestive problems. Horses need plenty of long-stem fiber to minimize various digestive disturbances.
The degree to which the forage fed to a horse has become stemmy has a major effect on its digestibility. Normal function of the horse’s digestive tract requires plant fiber.
Eating very stemmy hay can limit energy intake and cause an energy deficiency in sport horses. On the other hand, stemmy forage can be helpful for horses that gain weight easily. The more fiber there is in the feed, the more time it needs for digestion.
Hay, yes—but what kind?
The nutritional quality of hay is primarily affected by the plant’s stage of growth at harvest. Forage harvested at a late growth stage, with a high proportion of stem, typically contains a lot of fiber that is indigestible in the horse’s digestive tract, which reduces overall nutrient digestibility. The protein content of stemmy hay is often low and the sugar content high, because plants accumulate sugars in the stem. Leafier forage with less thick stem is made from younger growth, and its digestibility and feed values are generally better than more mature, stemmy hay. Other factors that affect the nutritional quality of hay include, among other things, the plant species used and their proportions, weather conditions at harvest, harvesting method, and pasture management.
With normal feeding, horses usually receive the necessary amount of fiber. A more common problem is an excessively high amount of poorly digestible fiber (for example, straw or overly stemmy hay). High intake of poorly digestible fiber reduces nutrient digestibility and absorption, and also leads to an energy shortage for hindgut microorganisms and a weakening of the microbial population, and it can increase what is often called a “hay belly.”
Especially if the amount of digestible fiber in the forage is not sufficient, or if the amount of hay has to be restricted for some reason, digestion can be supported with fiber-rich feeds. Dietary fiber is found in plant-based products: grains, vegetables, fruits and berries, as well as nuts and seeds.
Good additional fiber sources include, for example, hemp seed, chia seed, hemp bran, flax seed, beet pulp fiber, beetroot, sunflower and pumpkin seeds, blackcurrant berries, apple, and rosehip.
