Effects of Dietary Fat and Yeast Culture Supplementation on Total Tract Digestibility by Horses

The effects of different dietary fats on apparent total tract digestibility in growing horses were examined using an incomplete Latin square design in Exp 1. Four yearling horses - 2 fillies and 2 colts - were fed a completely pelleted diet containing different types of fat: no supplemental fat (control); 10% hydrogenated fat; or 10% soybean oil (SO). Horses consuming the control treatment had greater (P < 0.05) digestibility of DM, OM, total dietary fiber, and GE than did those fed the supplemental fat treatments. Horses consuming the SO treatment had greater (P < 0.05) digestibility of DM, OM, CP, fat, total dietary fiber, and GE than those consuming hydrogenated fat. The SO treatment had the least negative effect on nutrient digestibility compared with the control treatment. In Exp. 2, 8 horses were used in a replicated 4 × 4 Latin square design to determine the effects of yeast culture (YC) supplement on nutrient intake and total tract nutrient digestion when highfat and low-fat diets were fed. The lowfat treatments had greater (P < 0.05) digestibility of DM, OM, CP, and GE than high-fat treatments. There were no significant differences (P > 0.05) in nutrient digestibility of treatments containing YCcompared with no YC. There were no interactions (P > 0.05) between fat supplementation and YC supplementation. No effects of yeast culture supplementation on nutrient digestibility were noted when high-fat or low-fat diets were fed.