Horses in few disciplines require as much high-energy nutrition as racehorses. So it’s no surprise that, traditionally, a large part of a racehorse’s food ration is energy-dense concentrated feeds. But concentrates are hard on the equine stomach, contribute to gastric ulcers, and lack the bulk and fiber content that keep a horse’s gut healthy.

In an ideal world, horses—even racehorses—would thrive off forage alone. But given their intense training programs, could that ever be possible? Swedish researchers say yes, not only is it possible but it can also be beneficial.

The key is to ensure the hay, haylage, or grass has enough high-energy nutrient value to cover the horse’s needs, said Sara Ringmark, PhD, of the Swedish University of Agricultural Sciences Department of Anatomy, Physiology, and Biochemistry, in Uppsala.

“A high energy content is crucial for the function of a forage-only diet in racehorses, which is why regular analyses of the forage nutrient content should be performed,” she said.

If the forage is up to the required energy standards, racehorses should be able to thrive, without reduced performance, while maintaining good body condition, said Ringmark. In fact, in an earlier study, fellow researchers at the Swedish University of Agricultural Sciences found that a forage-only diet is associated with lower levels of lactic acid, meaning the horses physically cope with the training regimen better than they would on a mixed diet with concentrates.

In their current study, Ringmark and her fellow researchers followed 2- and 3-year-old Standardbred racehorses over a two-year period of intense training and racing. Throughout the study period, the horses received free-choice high-quality haylage (grass cuttings wrapped in plastic soon after harvesting to maintain nutrients) consisting mainly of meadow fescue, timothy, and ryegrass. Depending on the nutrient analysis of each batch of haylage, the scientists supplemented the forage with 0.25 to 1.0 kg of a pelleted lucerne product (95% lucerne, 5% molasses) per day to meet government-stated nutrient requirements. They also had access to a basic salt block as well as a mineral supplement based on the forage content to fulfill their mineral intake needs. But they had no concentrated feeds during this critical two-year period of growth and training.

Half the horses followed a standard training program, whereas the other half followed a reduced intensity program, consisting of approximately 30% less training. These were the same horses Ringmark used in another study comparing the effects of the training programs.

They found that feeding young racehorses the forage-only diet did not prohibit muscle glycogen storage, growth, or body condition scores (BCS), and it seemed to promote good nutrition-related health, she said. Specifically, there were no differences in feed intake or in any of the body measurements between the training groups, with an average BCS of about 5 (on a 1-9 scale). She also found no difference between groups in muscle glycogen content (a measure of muscle energy storage), and none of the horses developed nutrition-related disorders or stereotypies.

And, contrary to popular thought, these forage-only horses did not appear “big-bellied” or heavier than concentrate-fed racehorses, Ringmark added. “The forage used was cut at an early plant maturity stage, providing a feed with high fiber digestibility and a high energy content as opposite to a late-cut forage,” she said. “Previous studies have reported that horses weigh approximately 3 kilograms more when fed a forage-only diet. Our horses showed no signs of bulkiness in the belly, as can be seen in the photos.”

This diet also did not appear to affect performance, Ringmark said. The analyses of that aspect are still underway, so while they “don’t expect” to find any differences, it’s too soon to draw a definite conclusion.

“Feeding racehorses a forage-only diet is certainly contrary to tradition, but not to what the horses have evolved to be feeding on for millions of years,” Ringmark said. “There are a lot of health problems associated with feeding starch to horses as well as an increased risk of stereotypic behaviors. The welfare of the horse may therefore be favored by the replacement of high-starch concentrates to a high-energy forage.

“Moreover, when fed an early cut, high-energy forage, horses have shown a decreased plasma lactate response to submaximal exercise and a higher blood pH, which could be an indication that the forage-only diet could at least not impair performance capacity in Standardbreds,” she continued.

A forage-only diet should also be conceivable for Thoroughbred racehorses, she told The Horse, although studies need to confirm that theory. Hay could possibly be used instead of haylage, Ringmark said.

“As long as the nutritive value were the same I would not expect any large differences,” she said. “However, in some parts of the world, it may be difficult to harvest and dry hay at such an early plant maturity stage as required to reach the high energy content of the forage used in the study.”

Fresh grass might also serve as good forage, she added, but “it’s difficult to monitor nutrient content of what the horse is actually feeding on in a pasture, and the variation may be too large to use it as a long-term feeding strategy.”

It’s important to keep in mind that individual horses might respond differently to forage-only diets, she said. That’s why working horses on forage-only diets require a “thorough control of the nutrient content of the forage” as well as regular monitoring of the horse’s BCS. “But that, of course, is also true in horses fed concentrates,” she said.

The study, “Effects of training distance on feed intake, growth, body condition and muscle glycogen content in young Standardbred horses fed a forage-only diet,” was published in Animal