Changes in in vitro fermentative capacity of equine feces due to alteration of forage diet

Abstract

In vitro digestibility methods require a microbial inoculum source. In hindgut fermenters like equids, cannulation of the cecum is a high-risk procedure and can be avoided by using feces as a microbial inoculum source. The hindgut microbial population can change with an alteration of concentrate and forage ratios in equids. This study’s purpose was to determine if forage type fed to horses providing fecal inoculum alters subsequent in vitro digestibility estimates. Four mature mares were arranged in a 2 × 2 crossover design and used in a 4-wk study using two species of hay fed ad libitum: alfalfa (Medicago sativa) and Coastal bermudagrass (Cynodon dactylon). Each of two periods consisted of 7 d during which the mares were adapted to their respective diets, followed by feeding the experimental forage diet for 7 d. On d 14 of each period, feces were collected via rectal grab from each mare. Fecal samples (200 g) were blended with 400 mL of buffer solution under anaerobic conditions, filtered to remove large particulates, and placed into one of eight DaisyII (ANKOM Technology) incubation vessels. Filter bags were filled with 0.25-g samples of dried, ground alfalfa and bermudagrass to pass a 2-mm screen. Six filled filter bags of a single forage plus 2 blanks were added to each vessel before being flushed with CO2 and sealed for fermentation at 39.5°C. Half of the sample bags were removed at 48 h, and the remaining bags were removed at 72 h. Sample bags were rinsed with cold deionized water and dried at 60°C for 12 h before weighing for determination of percentage dry matter in fermentation residues. Dry matter disappearance (DMD) was calculated, followed by NDF and ADF determination. Using JMP Pro 12 (SAS Inc.), an ANOVA was performed. Significance was declared at P < 0.05. Results from the 48-h fermentation indicated that donor animal diet had no effect on DM, NDF, or ADF digestibility of bermudagrass, but at 72 h, DM digestibility estimates are higher with alfalfa-sourced feces. For alfalfa at 48 and 72 h, DMD, NDF, and ADF digestion were more extensive when fermented in alfalfa-sourced feces than bermudagrass-sourced feces. These results indicate that equids used as microbial inoculum donors for in vitro digestibility evaluations may need to be consuming the forage being studied, but further investigation is required.