A Quarter Horse training track covered in lush green grass fills the Zoom background behind Michigan State University professor and racehorse owner Brian Nielsen, PhD. As I’m interviewing him about managing horses on forage-only diets, he tells me the track is not only where he trains his racehorses but also where he pastures them.

“The root system holds in place better, and I can get on the track earlier in the spring,” helpful after long Michigan winters, says Nielsen, an equine exercise physiology professor in East Lansing. “But mainly, I thought, well, if I plant my track, it’s actually more grazing.”

Racehorses on pasture? Sport horses on hay without concentrates?

Absolutely, our sources tell us. And they’re all the better for it, so long as their owners know what they’re doing.

Getting Horses Back on Forage: A Growing Passion

Horses, we know, evolved as grazers. But as humans placed higher physical demands on work and sport horses, starch- or grain-rich concentrated feeds became popular ways to give the animals the extra energy they needed to perform, Nielsen says. Unfortunately, such feeds come at a cost to equine health, having been linked to gastric ulcers, obesity, and behavioral problems.

That’s why researchers across the globe have become passionate about promoting the idea that many horses can get sufficient energy through forage alone. Pat Harris, MA, VetMB, PhD, Dipl. ECVCN, MRCVS, an equine nutrition specialist and head of the WALTHAM Equine Studies group in the U.K., is arguably one of the most fervent.

“My passion is trying to explain to people that a lot of horses, ponies, and most donkeys can be managed on forage with a balancer,” Harris says. “It’s ­important that people recognize that forage should be the foundation of every single horse’s diet and that we need to provide enough forage to help support the health, welfare, and behavior of all the horses in our care.”

Sara Ringmark, PhD, of the Swedish University of Agricultural Sciences Department of Anatomy, Physiology, and Biochemistry, in Uppsala, is another forage-only proponent. Over the past few years her team has led multiple studies showing harness-racing horses can thrive on forage-only diets.

“You get all the health advantages, you get better metabolism for exercise, and you prolong feeding times,” she says. “It’s win-win.”

Better Health, Welfare, Performance, and Behavior

When the forage is good quality and the right type for a particular horse, it can significantly improve his overall health and welfare and even make him a better athlete, our sources say.

Horses evolved consuming a variety of grasses, leaves, and other plants over vast plains and steppes, says Nielsen. It’s in their nature to chew, salivate, swallow, digest, and defecate practically all day and night—keeping a near-constant stream of bulk and nutrients moving through the body.

By providing nutrients and energy in forage, owners give their horses the chance to have the prolonged meals their bodies are designed for, says Harris. Indeed, abundant chewing and salivating is part of the repertoire of normal equid behavior and affords them better welfare, she says. “They’re effectively hot-wired to chew!” she says. “It’s good for their minds, and it’s good for their whole digestive tract.”

Forage also typically contains very little starch, a component that can provoke gastric ulcers and increase the risk of colic, Ringmark says.

“By reducing starch intake, we decrease the frequency of such health problems,” she says.

A fiber-rich diet might also improve performance by spurring horses’ metabolism to burn more fat within the muscle, Ringmark adds. As a result, their muscle cells create less lactic acid, which is ­associated with fatigue. Horses on forage-only diets exercise longer before lactic acid starts to accumulate, meaning they have more stamina than horses on forage plus concentrates, she says.

Forage-rich diets are also better for the intestinal microbiota, she says. “It’s more stable, less sensitive to changes.”

When the forage is pasture, horses benefit from the natural movement associated with grazing, says Nielsen. “A lot of the injuries horses develop are because we mismanage them like sticking them in stalls all day,” he says. “But if horses are living on pasture, they’re running around, stimulating their bones.” Like muscles, bones can become stronger from regular exercise—particularly if horses are allowed to do short sprints, he explains. That could reduce the risk of injury, Nielsen says, and support better performance.

The ‘Right’ Forage Crop and Cut

Feeding the right forage in the correct amount is key to success, says Harris. Each equid is an individual and has different nutritional requirements depending on breed, genetics, age, activity level, reproduction status, and more.

Forage quality varies in multiple ways, starting with the plant species itself, she says. For example, cool-season grasses like orchardgrass or fescue in the U.S. or English ryegrass and timothy in the U.K. tend to be higher in sugar content, even at the same stage of maturity, than warm-season grasses such as Bermuda and modified crabgrass—which are more common in warmer parts of the U.S. Time of year, fertilization status, environmental conditions, and time of day can also affect sugar content. 

Grass maturity makes an important difference, as well, Ringmark says. Short, less mature grass is more digestible and much richer in energy and proteins.

Combined, these factors can make critical differences in a forage’s nutritional content, she explains. In general, rich grass provides the most energy, which is key for feeding many horses. But it’s not what you want for horses at risk of obesity or metabolic disease.

“There’s no point feeding a very immature, energy-rich forage to a fat pony; it’s inappropriate,” says Harris.

Owners of horses with endocrine issues such as insulin dysregulation can provide low-sugar forage (or soak the hay for 30 to 60 minutes to reduce sugar content, being sure to toss the water out before feeding) paired with a ration balancer.

Of course, people can try managing their horses’ weight by giving them more or less hay, Harris says. But it’s better to avoid cutting the amount fed, which defeats an important point about forage-rich diets: spending much of the day chewing and swallowing. And it might not even be possible to sufficiently increase the intake of mediocre hay for horses with high energy needs. Such a ration also increases bulk in their digestive systems and could lead to hay bellies.

Smart Storage Sense

Knowing how forage is stored makes a difference both for calculating rations and ensuring it’s safe for horses to eat.

Haylage, for example, is preserved ­effectively by being wrapped in an airtight binding; silage does so with even greater moisture content, enabling a beneficial fermentation process to occur, ­Ringmark explains. Such storage is especially appropriate for early-cut forage, which contains more moisture. But those advantages run out within days of opening the plastic, as air creeps in and causes unwanted bacteria to proliferate and mold to develop.

Hay loses nutrients during the drying process, even before baling, as well as in storage, explains Harris. This reinforces the need for a ration balancer.  

The way the forage was preserved also affects the amount of dry matter—a critical point, given most equids should be eating at least 1.5% of their body weight every day in dry matter. Dry matter is not the same thing as the total weight of the preserved forage fed to a horse. Baled hay is usually 85-90% dry matter, meaning the rest of the weight is moisture (even if it feels completely dry). But haylage varies dramatically in its dry matter content; while it’s generally 60-75% dry matter, it can range from 50% to nearly 90%. In other words, there’s almost always more dry matter in hay than in haylage, so getting to that 1.5% body weight in dry matter might require more haylage than hay. But because haylage is typically higher in energy (calories) than many hays, feeding it at a rate to meet your horse’s dry matter requirement might exceed his energy needs.

Hay baled with more than 15% moisture (less than 85% dry matter) is likely to become moldy, which can threaten horses’ respiratory as well as general health, says Harris. But even lower-­moisture hay can get wet and become moldy due to baling or storing ­conditions.

All hays contain some mold and fungi, but steaming could potentially make hay safer to feed without affecting nutritional quality, Harris explains.

“If you want to feed hay to horses with respiratory issues in particular, it may be advantageous to steam first—although you should always start with as good, hygienic, quality hay as possible,” she says. Steaming is tricky business; it must be done properly—at the right temperature and under the right conditions—to be effective.

The Critical Balancing Act of the Ration Balancer

Despite all its benefits, forage is still rarely sufficient to meet many horses’ nutritional requirements on its own, our sources say. Depending on the geographic region, season, grass species, cut, and storage methods, forage can contain varying amounts of important vitamins and minerals—which can affect horses’ health, whether they’re in work or not. 

“You know those wild horses that lived on forage alone and seemed to do just fine?” Nielsen says. “Well, the question is, did they do fine, or did they die at age 12? Sometimes that long-term deficiency might not show up right away. But it might show up eventually.”

People could get hay bales and sections of pasture analyzed regularly to try to create a custom mix of extra nutrients, but that’s not very realistic in terms of timing, effort, and expense, he says.

Fortunately, commercial feed balancers offer a good blend for topping off forage, says Ringmark. “We usually get a surplus of the minerals, because we already have them in the forage,” she says. “But it’s never been way out of range. It works.”

Even so, she says she’d like to see more balancers tailored to horses on forage-only diets and adapted to local conditions.

Ringmark’s study horses get enough protein, calcium, magnesium, and phosphorus in their Swedish haylage, she says. So they usually only add balancer containing sodium and trace elements.

In typical U.K. and many U.S. grass hays, the nutrients are sometimes insufficient even for horses in low-intensity work, Harris says. So balancers must provide sufficient-quality protein and essential amino acids, as well as vitamins, minerals, and trace elements. Because alfalfa hay is usually high in protein, protein-rich balancers aren’t usually necessary on an alfalfa-based diet.       

The Wrong Way To Do Forage-Only

While many horses can live well off forage alone, such diets often fail, our sources say, usually due to human error. “You have to know a few things about forage and diet before you can do this successfully,” Ringmark says. “If you try without the right knowledge and without the right food, there’s a big risk that you’ll fail and have a bad experience.”

People must also recognize the signs of failure, adds Harris. “If you don’t provide horses with enough energy, they’ll be thin and often lack energy,” she says. “If you provide them with too much energy, they’ll be fat or very excitable or both. If you don’t provide enough good-quality protein, they’re not able to develop the muscles you want.”

Other factors, such as training or underlying pain, can also cause or contribute to body condition and muscle-associated issues, she says. And, again, the consequences of insufficient vitamins and minerals might not show up for years or only under certain circumstances, such as challenges to the immune system.

Implementing a successful forage-only program requires education and, ideally, assistance from qualified nutrition experts.

“There’s always going to be an art to feeding horses and looking at the horse and knowing how they’re performing,” Nielsen says. “But that still goes with a lot of guesswork.”

Take-Home Message

With digestive systems designed to break down fiber consumed throughout the day, horses often benefit from better physical and mental health when they’re fed forage-only diets with added vitamins, minerals, and protein to meet their nutrient needs. Education, experience, and expert guidance can help owners learn to keep even their athletic horses happy, healthy, and performing well without having to feed large amounts of starch- and sugar-rich concentrates—provided they can acquire forage of sufficient ­quality. “There are a lot of things to think about when you’re feeding forage-based rations, and there are lots of decisions to be made,” Harris says. “But doing so can be very beneficial.”