Haylage and grass hay are popular forage options for horses and ponies, but differences between the two products make them suitable for different groups of horses. Haylage contains at least 50% dry matter and is stored in airtight conditions, while grass hay is preserved for long periods by drying to a much higher dry matter content of at least 85%, said Ashley Fowler, PhD, a nutritionist with Kentucky Equine Research in Versailles, Kentucky, during her presentation at the Equine Science Society’s Symposium, held June 6-9 in Grapevine, Texas.

“Haylage is often a good option for horses that need a restricted diet because it increases their time spent eating, which might help reduce their risk of ulcers and stereotypies,” she explained.

This type of forage can also have higher protein and lower water-soluble carbohydrate (WSC) content than grass hay of the same species, maturity, and harvesting conditions. The researchers hypothesized that while the digestibility of haylage and grass hay might be similar, horses fed grass hay will have a greater glycemic response than in those fed haylage.

Fowler and her team designed a study to determine the effects of feeding haylage versus timothy hay in four Thoroughbred geldings over two 28-day periods. The horses were fed timothy-ryegrass haylage during one period and timothy hay during the other. They were fed a forage-only diet at 1.5% of their body weight on a dry matter basis, with the exception of one horse fed at 1% to minimize uneaten hay.

To perform a glycemic response test, the researchers fed the horses 25% of their daily dry matter allotment and took blood every 30 minutes for eight hours. Over the last seven days of each study period, they used fecal collection harnesses to collect feces and calculate the digestibility of each forage.

As expected, the researchers found that the horses took longer to finish their meals when fed haylage. “The horses’ peak blood glucose concentrations were higher when they were fed grass hay, likely due to the greater nonstructural carbohydrate (NSC) concentration in the hay,” said Fowler. Grass hay also had greater dry matter digestibility and digestible energy.

“The fiber digestibility of haylage was lower than we expected, and the horses developed free fecal water syndrome (a sign of low digestibility) when fed haylage,” said Fowler. “Fecal water holding capacity and fecal sodium concentration were greater in horses fed haylage, which may have contributed to the development of free fecal water.”

Horse owners should work with their veterinarian and an equine nutritionist to determine which forage option is best suited to their horse. Typically, haylage is best for hoses who cannot consume a large quantity of hay or require low NSC forage; however, it is important to examine each horse’s individual needs before making changes to their feeding program.