Feeding horses based on their gastrointestinal (GI) tract design and biological needs can help improve their gut and overall health. Their small stomach capacity is best suited for grazing and consuming small meals throughout the day.

“A good feeding program will provide adequate energy and feed for (a horse’s) gut health by providing long-stem fiber needed to ensure the gastrointestinal tract is moving well and consistently,” said Robert Bray, PhD, professor emeritus at California State Polytechnic University, in Pomona, and consulting equine nutritionist for Star Milling Company, in Perris, California, during the 2024 EquiSummit virtual conference, held Dec. 3-4.

To feed horses by gut design, Bray said owners should follow two important rules for feeding fiber: the 1.5% rule and the 50% rule.

What is Fiber?

“Fiber is the horse’s primary fuel source that is digested by microbes in the large intestine,” said Bray. “Fiber promotes GI tract movement and when the horses chew, it produces saliva that buffers the foregut (everything ahead of the cecum). Fiber nourishes the gut microbes, promoting microbial diversity and stabilizing the pH of the GI tract. “Fiber also establishes the rate food moves through the GI tract.”

Bray described fiber as the cell wall component of a plant cell. In contrast, the contents of the cell include the starches, proteins, sugars, trace minerals, etc.

He emphasized that fiber is not considered a nutrient, yet it is an essential component of the diet, often noted on feed tags as “crude fiber.”

The 1.5% Rule for Feeding Horses FiberHorses need to eat at least 1.5% of body weight per day in fiber. So, an average 1,000-pound horse needs 15 pounds of fiber.

Fiber can come from a variety of sources and be found in different amounts depending on the type of forage. For example, 15 pounds of timothy hay provides 4.5 pounds of crude fiber, or 2,043 grams per day (based on 30% crude fiber).

“Other grass hays have similar levels of crude fiber such as teff, Bermuda, orchardgrass, and oat hay,” said Bray. “But let’s look at alfalfa hay that owners commonly feed.”

Fifteen pounds of a reasonable-quality alfalfa offers only 1,736 g of crude fiber per day, which is much lower than the crude fiber in grass hays noted above. “This alfalfa example will only fill 86% of the horse’s fiber requirement,” said Bray.

The 50% Rule of Feeding Horses Fiber

Because alfalfa hay does not fulfill a horse’s fiber requirement, it should not exceed 50% of the total forage because pound per pound it contains less fiber than grass hay.

“In addition, horses will often select the alfalfa leaves instead of the stems, so they are getting even less fiber,” said Bray. “Even though alfalfahas less fiber, it has higher energy (more calories) than the grass hays so, to maintain body weight, they (horse owners) need to feed less, which means they (horses) get even less fiber.”

If we split alfalfa 50/50 with timothy hay, we are still only feeding 94% of the horse’s total fiber requirement, he explained, but it’s better than alfalfa alone.

“If you feed a more mature grass hay, then the fiber content will increase even more,” said Bray.

Regardless of the type of hay your horse eats, feeding it in a slow feeder might improve GI tract motility, stimulate saliva production to buffer gastric juices, and decrease time between feedings.

Looking at Processed Forages and Complete Feeds

Just like long-stem alfalfa, horses should not consume more than 50% of their dietary fiber in the form of alfalfa cubes or pellets. Processed forages and hay offer the same level of digestibility.

“Cubes have less volume which induces less GI tract contraction/gut motility and stimulates less water consumption,” said Bray. “This is a negative. In addition, feeding intervals are longer because they consume the cubes and pellets quicker, leaving them with an empty gut.”

Bray, who admits he’s not a fan of complete feeds—designed to meet all of a horse’s nutritional needs, including forage—explained, “If you look at fiber requirements, 15 pounds of a complete feed only fulfills 81% of the horse’s fiber requirements. This is far off from the target.” To meet those requirements, you’ll need to supplement with additional forage.

Other Fibers for Horses

Beet pulp and soy hulls are also referred to as super fibers, but Bray prefers the term soluble fibers. These fibers contain pectins and oligosaccharides (short carbohydrate chains), which horses digest in the small intestine unlike regular fibers that are digested in the large intestine.

“One pound of soy hulls or beet pulp can provide a significant amount of fiber,” said Bray. “Still, it is important to provide adequate long-stem forage to promote GI tract motility.” Beet pulp is typically soaked and soy hulls softened with water.

Take-Home Message

Long-stem grass forages fulfill a horse’s daily fiber needs when fed at 1.5% of his body weight per day. These promote GI tract motility, stimulate saliva production to buffer gastric juices, and decrease the gap between feedings, especially if fed in a slow feeder.

Additional 2024 EquiSUMMIT Coverage:

• Tackling Equine Gastric Ulcers
• Investigating Prebiotics’ Role in Managing Equine Leaky Gut
• Benefits of Extruded Horse Feeds
• What Happens With the Horse’s Gut in the Heat?
• The Equine Microbiome and Immunity