Forage: A Fluid Reservoir for Horses

Ingested forage holds water in the horse’s gut. This is seen as positive in endurance horses, as the stored fluid can be drawn upon to keep the horse hydrated as it covers the miles during a long ride. Trainers of Thoroughbred horses see the weight as a disadvantage that has the possibility of causing a horse to run more slowly in a short race, so they routinely remove hay from a horse’s stall in the hours prior to competition.

A recent study conducted at Michigan State University looked at type of forage and length of forage particles as related to their water-holding and water-releasing properties. Grass hay had the highest rate of water absorption and also showed the greatest potential for early liquid release, while alfalfa hay held much less water. Chop length was important for water-holding ability, with longer forage pieces holding fluid more effectively than shorter pieces.

Based on this study, grass hay might be the best forage for endurance horses, while alfalfa hay might be a better choice for Thoroughbreds in the days leading up to a race.