The Effect of Feeding Horses a High Fiber Diet With or Without Exogenous Fibrolytic Enzymes Supplementation on Nutrient Digestion, Blood Chemistry, Fecal Coliform Count, and In Vitro Fecal Fermentation

Abstract

Sixteen Quarter Horse mares (450 to 500-kg body weight) were used in a complete randomized design to determine the effects of feeding a high fiber diet with or without exogenous fibrolytic enzymes on nutrient digestion, blood chemistry, fecal coliform count, and in vitro fecal fermentation. The treatments comprised feeding the horses (1) a basal diet without enzyme addition (control); (2) control diet plus cellulase at 10 mL/mare/d (CELL); (3) control diet plus xylanase at 10 mL/mare/d (XYL); or (4) control diet plus a mixture of 5 mL cellulase and 5 mL xylanase/mare/d (CX). The basal concentrate diet consisted of a mixture of 50% commercial concentrate and 50% wheat bran fed at 4 kg/horse, offered twice daily at 04:00 and 16:00 hours, and oat straw offered ad libitum at 05:00 and 17:00 hours. The enzyme allocation for each day was mixed with 1 kg of concentrate diet at 04:00 hours, and the experiment lasted for 15 days comprising 10 days of adaptation and 5 days for sample collection. The in vitro cecal fermentation with addition of 2 μL/g dry matter (DM) of each enzyme (CELL, XYL, and CX) to a basal diet of oat straw and concentrates mixture (1:1 DM) as a substrate was carried out. The mares fed enzyme-supplemented diets had greater (P < .01) oat straw and total nutrients intakes compared with the control diet. Feeding enzyme-supplemented diets increased total nutrients digestibility (P < .05) and blood total protein (P = .0277) compared with the control. Feeding XYL-supplemented diet increased blood alanine transaminase and aspartate aminotransferase concentrations (P < .05) compared with control treatment. Lower fecal coliform count was obtained (P = .0114) with mares fed CX diet compared with control mares. The XYL and CX treatments had decreased asymptotic gas production (GP) (P = .0173) with lower rate of GP (P = .0412) compared with CELL treatment. CELL and XYL treatments had decreased (P = .0394) lag times compared with control and CX treatments. At 24 hours of incubation, CELL and XYL treatments decreased methane production (P = .0131), whereas CX treatment increased its production at 48 hours (P = .0202) compared with control treatment. No effect was observed (P > .05) with enzymes addition on carbon dioxide production at different hours of incubation compared with control treatment. Higher in vitro DM degradability values (P = .0092) were obtained with the enzyme treatments compared with control treatment. Fermentation pH was lower (P = .0396) with CX treatment and increased with CELL treatment compared with the control and XYL, showing a greater pH with CELL than the other treatments. It can be concluded that addition of fibrolytic enzymes at 10 mL/mare/d improved feed intake and nutrients digestibility without affecting mare's health.