Influence of yeast culture supplementation on ration digestion by horses

Summary Four 3-year-old Quarter Horse geldings were assigned to dietary treatments in a 4 × 4 Latin Square crossover design to determine the digestibility of a basal diet supplemented with 4 levels of yeast culture. The basal diet consisted of a corn/rice hull base textured concentrate and commercially processed alfalfa cubes. Diets were formulated to meet nutrient requirements for horses in light training 13 and were adjusted to maintain body weight. Diets were supplemented with 0, 10, 20 or 40 g/hd/d of yeast culture. During the experiment, each trial consisted of a 10-day preliminary feeding period, a 5-day total collection period, followed by a 3-day rest period. A harness equipped with a collection apparatus was used to collect the feces and urine. Apparent digestibilities of dry matter (DM), ash, crude protein (CP), gross energy (GE), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose and lignin were not different (P>.05) between the supplemented and unsupplemented diets. All horses were in positive nitrogen balance throughout experiment. Nitrogen balance was not affected (P>.05) by treatments. The lack of a significant difference between yeast culture supplementation and digestibility suggests that either not enough yeast culture was fed or that the yeast culture was digested and utilized as a nutrient source, rather than for enhancing fermentation in the lower gut. Also, rice hulls furnished the major bulk of the diet and because of their indigestible nature, they may have contributed to the lack of a significant treatment difference.