Fun With Feed Math! Part 2: Rules to Feed By

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Written By Dr. Kris Hiney

Now that we have finished our discussion concerning our horses energy requirements, we are going to turn our attention to how best to deliver those calories to our horses. Over the next few months, we will discuss many confusing issues facing horse owners concerning the type, quantity, and quality of our feeds. As horse owners are barraged with information concerning grazing, metabolic syndrome, obesity and ulcers, it is sometimes easy to get lost in the conflicting information. So we are going to take it step by step, and do our best to understand these complex issues. Hopefully we all know that our duty as horse owners is to feed our horses a diet which maximizes their health, both physically and mentally. This month we will discuss strategies for feeding horses that will optimize not only the health of their digestive system, but keep them mentally sound as well. To understand how best to feed horses, we first need discuss the true nature of a horse prior to its domestication and modern management practices.

How the horse got started.

Horses certainly didn’t evolve on the lush pastures of Kentucky behind beautiful wooden fences. They were plains animals who drifted about continuously looking for sources of food. Horses successfully existed through times of rapid growth of grasses in the spring but also through the dormancy of fall and winter, times of drought etc. Compare that idea to horses who now have laminitis issues with grazing lush pastures! If we examine how horses naturally forage, they are selective grazers who seek out the most nutritious plants at particular stages of growth. Thus they moved continuously as they look for plants with greater palatability, and presumably more nutritional value to the horse. Feral horses will typically spend from one half to two-thirds of their day grazing, moving continuously as they graze. That means horses are meant to eat small amounts continuously and to travel extensively as they do so. Studies on grazing horses have shown that typically horses will cover 1-3 miles per day as they forage.

Grazing too much?The amount of time foraging is dependent upon the nutrient density of the pasture. The more sparse the vegetation, the more need for grazing time. Imagine wandering on the open plains searching for feed compared to grazing on well manicured pastures in Kentucky! On modern pastures that are managed well and improved with fertilization and seeding, it does not take as much time for the horse to meet its nutrient requirements. That is why we often see horses managed on pastures which are able to get fat, compared to feral horses. They are also confined to a greater extent, and thus may not be getting the amount of exercise a feral horse would receive. Additionally, many breeds of horses were originally selected from individuals who were more efficient at using feed. Think of our more docile breeds who have an easy going temperament. This personality type is often linked with the “thrifty” genotype. These guys (think ponies, Quarter Horses, Morgans, etc.) often have more problems with obesity and obesity related issues. In fact, this is such an important, and confusing, issue, we will address this problem specifically in an upcoming issue.

Let’s look on the inside!

From what we stated previously about the “normal” life for a horse, the horse’s digestive system is designed to deal with small amounts of food taken in continuously throughout the day. When we look at a horse’s digestive system, this easily makes sense. In comparison to our dogs, or cats, a horse’s stomach makes up a relatively small percentage of its entire tract. The stomach makes up about 10% of the entire tract, while the hind gut of the horse comprises 65% percent of the horse’s digestive capacity. While carnivores are considered to be opportunistic meal feeders (Eat as much as possible when you catch something because you never know when your next meal is coming!) horses are designed to eat small amounts (or continuous steady intake) throughout the day. The rate of passage, or how fast food moves out of the stomach, is fairly rapid. Two hours after eating, half of the solid particulate matter has passed out of the stomach, with ingesta reaching the hind gut within 5 hrs, while the stomach will be completely empty 10 hours post feeding.

So what does this mean for the horse? Interestingly, the horse’s ability to salivate is directly tied to mouth movements. In other words, they salivate when they chew. In other species, such as cattle, the salivary glands continuously produce saliva, of which a significant component is sodium bicarbonate. This continuous salivation buffers the rumen (or the foregut) of cattle and helps to prevent a drop in pH (or preventing an acidic environment). Compare this again to our meal feeders, (dogs, cats, and us), which salivate when we anticipate a meal. This helps the food slide down the esophagus with greater ease. Horses in the natural state have a relatively steady supply of saliva entering their stomach, with buffers included, as they graze throughout the day. However, compare the natural state to what happens when we manage horses in the typical box stall setting. Horses are provided with feed twice a day, with sometimes a prolonged period of time between their evening meal and the morning feeding. When the horse has not been provided with feed after 5-6 hours, the pH of their stomach begins to drop. This is why feeding strategies can directly impact our horse’s health. With a repeated drop in pH, the horse becomes susceptible to ulcers. Couple this with other risk factors for ulcer development and we can get a pretty unhappy horse. So our first rule of feeding horses is to provide enough forage to prevent the horse from being without anything to eat, ideally for less than six hours but at least avoiding a completely empty stomach 10 hrs post eating. Next month we will discuss ulcers in horses in depth.


From a riding perspective, we like it when horses salivate when they are ridden. This is typically equated with a horse being “soft in the face or jaw”. These horses are using their jaw and tongue and thus are not locked or stiff through the jaw resisting the rider. We often use bits that have a copper component which encourages salivation. Ever put a penny in your mouth? What happens? As horses salivate they will swallow, and this again helps to prevent a horse from stiffening through his jaw.

The stomach of the horse is not the only part of the digestive tract we need to be concerned with. As horses are designed to graze, their natural diet consists of longstem forages. While they possess the digestive capacity to utilize grains such as corn and oats, these would not make up a significant portion of the horses’ natural diet. However, we sometimes need to supply our horses with more energy dense sources of feeds when their energy requirements go up, such as moderate or intense exercise. We may also find ourselves sometimes short of hay due to prices, drought, supply shortages etc. Thus we may need to look at alternative feed sources than our typical baled hay. However, as horses are designed to ferment forages in their cecum and hind gut, it is important that we keep that fermentation functioning properly. To ensure this proper function, we need to feed horses at least 1 % of their body weight in forage per day. That means if your horse weighs 1200 lbs, it should never receive less than 12 lbs of hay or forage per day. Now if you actually weigh that out, you would see that really isn’t that much at all. Ideally, the horse should receive closer to 2% of their body weight in hay per day. So double that 12 lbs to 24 and you will be much closer to what the horse would naturally consume. On their own, horses will consume about 2-3% of their body weight per day. How we provide that amount, or if we provide that amount of feed, is up to us.

For horses that have high energy requirements, it may be necessary to provide them with extra concentrate. However, large meals of concentrates may not be great for gut health. If the rate of concentrate intake exceeds that of the horse’s ability to digest it in the small intestine, it escapes to the hindgut of the horse. Here, there are types of bacteria that will thrive on this meal of simple carbohydrates. Unfortunately, this carbohydrate fermenting bacteria will produce more acidic by products. The lowering of pH in the hindgut can set off a chain of unhealthy events, including laminitis, colic, diarrhea etc. Thus, horses should never be fed concentrate meals (the grain portion) in levels of over 0.5 to 0.6% of their body weight at one time. Beyond this point, we exceed the capacity of the horse’s small intestine to digest and absorb the meal. For our 1200 lb horse, that means that his grain meal should never be over 6-7 lbs. If the horse truly requires that much grain (12-14 lbs per day), the best solution would be to split the concentrate into multiple, smaller meals.

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