Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2001
Publication Date: N/A
Citation: Interpretive Summary: Polydextrose (PD) is carbohydrate used as a synthetic fat substitute because it has many physical properties of fat, but is digested to only a small extent in the human digestive tract. PD is occasionally available for sale as an animal feed, but little is known about its digestion in cattle or other ruminants. We determined that PD is metabolized in a complex fashion by ruminal bacteria. A small fraction of the PD is digested rapidly to produce a fermentation product mix useful to the animal. However, most PD is digested even more slowly than is fiber. Pure cultures of individual species of ruminal bacteria varied greatly in their ability to utilize PD, but again, PD was fermented much less effectively than was starch. The fermentation properties of PD suggest that this material, even if available at competitive prices, is not an effective substitute for starch. This research will be of interest to dairy and beef producers who will use this information in ration formulation.
Technical Abstract: Polydextrose (PD) is a synthetic additive to human foods that has many physical properties of fat, but is poorly metabolized by monogastric animals. PD was fermented in vitro by mixed ruminal microorganisms, but the kinetics of the fermentation were complex and varied with different ruminal inocula. Gas production during digestion of PD was described by a two-pool digestion model. One pool, which contained 20-48 per cent of the substrate, was fermented without a lag period and at rates similar to that of potato starch or corn starch. The second pool was fermented considerably more slowly than was cellulose. The acetate/propionate ratio in products of PD fermentation ranged from 2.7 to 3.5. Growth rate of Selenomonas ruminantium D was higher on PD than on starches, while the reverse was true for Streptococcus bovis JB1, Prevotella ruminicola B14, and Butyrivibrio fibrisolvens H17c. For all four strains, the low final culture densities obtained suggest that only the easily-degraded oligomeric fraction of PD was utilized. The fermentation properties of PD suggest that this material, even if available at competitive prices, is not an effective substitute for starch.