Evaluation of the Effects of Live Yeast Supplementation on Apparent Digestibility of High-Fiber Diet in Mature Horses Using the Acid Insoluble Ash Marker Modified Method

The objective of this study was to evaluate the effects of live yeast (LY) in a high-fiber diet on nutrients digestibility in mature horses. Six Italian Standardbred mares (weight: 544 ± 14 kg; age: 15.30 ± 3.9 years) in a two-period crossover design were fed a basal diet (2.5% body weight BW]) in a 70:30 forage:concentrate ratio with (LY) or without (CTR) the administration of 4.6 × 10¹⁰ colony forming unit (CFU)/d of Saccharomyces cerevisiae (MUCL 39885). An adaptation to the diet of 14 days, and an 18-day administration phase, with fecal collection in the last 3 days were performed for each period. Yeast was top-dressed twice a day during the concentrate meal (12:30 am and 09:00 pm). Change in BW was measured at the beginning of each experimental phase and the diet adjusted accordingly, and individual feed intake was recorded daily. Concentrate samples were collected at the beginning of each confinement period and individual hay samples were obtained for each confinement day 38 hours before fecal collection. No influence of LY was observed on BW change (P = .64), feed intake (P = .48), hay intake (P = .48), or concentrate intake (P = .47). S cerevisiae supplementation improved apparent digestibility of dry matter (64.5% vs. 60.1%, P = .03), organic matter (66.1% vs. 61.6%, P = .04), neutral detergent fiber (42.5% vs. 35.9%, P = .04), and acid detergent fiber (36.5% vs. 28.0%, P = .03) with a positive trend on crude protein (P = .08). In the present study, the administration of LY to horses significantly improved the digestion of the fiber fractions of the diet.