The results of a trial aimed at studying the effects of a commercial polyherbal digestive tonic, Ruchamax®, on the feed intake, apparent digestibility, fermentation and microbial digestion of lucerne and wheat straw in Arabian horses are reported. Six Arabian mares, aged three to four years and weighing about 400 kg, received a diet containing 65% forage, consisting of lucerne and wheat straw, and 35% concentrate for two phases of ten days; the first phase without any digestive supplement and the next phase with an additional 15 grams of Ruchamax® per animal per day. Feed intakes were measured daily, and apparent digestibility, cecal digestion, and fermentation were assessed at the end of each phase. In vitro gas production was assessed to determine the fermentation and gas production of lucerne and wheat straw. Digestibility of dry matter and neutral detergent fiber was also determined for each phase. Ruchamax® increased (p < 0.05) feed intake; apparent digestibility of dry matter, crude protein, neutral detergent fiber, and acid detergent fiber; the potential of gas production; and microbial biomass efficiency for both forages. However, Ruchamax® did not affect cell wall degradability, partitioning factor, microbial biomass, amount and ratio of volatile fatty acids, and in vitro digestibility of dry matter, crude protein, neutral detergent fiber, and acid detergent fiber. Besides establishing the positive effects of Ruchamax® supplementation on cecal digestion and fermentation in horses, our findings also uphold the functional equivalence of the equine hindgut to the ruminant forestomach.