Effect of yeast culture on in vitro fermentation of a high-concentrate or high-fiber diet using equine fecal inoculum in a Daisy II incubator

¹ Department of Applied Sciences, Black Hawk College-East Campus, Kewanee, IL
² Department of Animal Science, Oklahoma State University, Stillwater, OK

^* To whom correspondence should be addressed. E-mail: steven.cooper{at}okstate.edu.

	Abstract

Two separate experiments were conducted to evaluate the use of a closed system fermentation apparatus (Daisy II incubator) and determine the effects of a yeast culture (YC) preparation (Saccharomyces cerevisiae) on in vitro microbial populations, diet digestion, and fermentation patterns in horses. In Exp. 1, 4 mature horses were fed a pelleted concentrate and alfalfa cubes in a 50:50 ratio. Fecal samples were taken from each horse to form the inoculum and placed in 4 separate incubation vessels. Twenty nylon bags (10 with 0.25 g and 10 with 0.50 g of the total mixed diet) were placed in each vessel, and in vitro fermentation was carried out for 48 h to determine DM, NDF, and ADF digestibility. In Exp. 2, fecal samples were taken from 4 mature horses consuming either a high-concentrate (HC) or high-fiber (HF) diet. Filter bags containing either the HC or HF diet were added to the 4 incubation vessels along with their respective inoculums. Yeast culture was added to 2 of the vessels containing either the HC or HF diet, while the other 2 vessels served as controls. Vessels were incubated as in Exp. 1 with samples taken at 24 h and 48 h. Filter bags were used to determine DM, NDF, ADF, and OM digestibility, while vessel fluid was analyzed for lactate, ammonia, VFA, and microbial concentrations. Results of Exp. 1 indicated that DM, NDF, and ADF digestibility were greater (P < 0.05), while the corresponding CV was lower (P < 0.05) for the 0.25 g vs. the 0.50 g sample size. In Exp. 2, YC tended (P = 0.10) to decrease ammonia concentrations in the HF diet and increased (P < 0.05) acetate production in the HC diet when compared to the control. There were no effects of YC on pH, lactate, or the measured microbial populations, as well as DM, NDF, or ADF digestibility. Results did, however, show that in vitro and in vivo DM digestibility estimates were extremely similar within a diet. Data from Exp. 1 indicated that the 0.25 g sample size provides a more accurate estimate of DM digestibility with less variation. Although YC had little, if any, effect in Exp. 2, results indicated that the Daisy II incubator does provide valid estimates of total tract DM digestibility in the horse. These data provide further evidence that this process would be an effective and practical means of approximating digestibility of diets with varying concentrate to forage ratios.

Key Words: in vitro fermentation, Saccharomyces cerevisiae, yeast culture