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Resistant starch was evaluated for energy value using fine silica and normal starch as controls and young rats as a test model. The net increase in rats' carcass energy due to the test materials fed over a 3‐wk period formed the basis for assessing energy value. Rats fed normal starch deposited about twice as much fat and significantly more protein in the carcass than those fed either resistant starch or silica. Rats fed resistant starch or silica showed similar growth responses and increases in components of body composition and carcass energy content. This suggested that resistant starch provided, like silica, no energy.

Objective: Prebiotics are used to support the gastrointestinal health via stimulating particular beneficial parts of the autochthonous microflora and enhancing their metabolism. Horses often suffer from gastrointestinal disturbances after feed changes or behavioral stress in response to transport. Therefore, the supplementation with prebiotic compounds might reduce the risk for intestinal dysregulation. The aim of this study was to investigate the influence of supplementation with Jerusalem artichoke meal (JAM) in a recommended prebiotic dosage on fermentation characteristics in the equine gastrointestinal tract.Methods: Twelve adult healthy horses received crushed oat grains (1.2 g starch/kg BW x d -1 ) and meadow hay (as fed basis; 1.5 kg/100 kg BW x d -1 ). Additionally, they were fed either an apparently prebiotic quantity of fructooligosaccharides (FOS) and inulin (0.2 g/kg BW x d -1 ) via Jerusalem artichoke meal (JAM) or an equal amount of maize cob meal without grains as control (CON) over 3 weeks. On d21, horses were euthanized, gastrointestinal contents were removed from 7 different regions of the gastrointestinal tract, the dry matter (DM) content, pH value and concentrations of short chain fatty acids (SCFA), L-and D-lactate and ammonia were measured.Results: JAM did not had a significant (P < 0.05) effect on any of the measured fermentation products and the pH value as well. Numerically, JAM increased the concentrations of SCFA (P > 0.05), lactate (both isomers, P > 0.05) and ammonia (P < 0.05) predominantly in the stomach but had no impact on the pH value overall. In the hindgut, the stimulation of the microbial activity was limited to the ventral colon only indicated by slightly higher SCFA (P > 0.05) and ammonia (P > 0.05) but lower L-lactate (P > 0.05) concentrations compared to control. Conclusion:FOS and inulin from JAM seem extensively be fermented already in the stomach of horses. The resulting organic acids might elevate the risk for gastric ulcers. Recently the gastric pH was buffered by concomitantly elevated ammonia, which requires a careful delineation of the influences of either individual acids or low pH levels or both together on the mucosa health in both distinct parts of the equine stomach. In the hindgut, the effect of JAM on the microbial activity seems to be much less pronounced than expected or advertised.

Four bulking agents-white wheat fiber, polydextrose, isomalt and oligofructose-were evaluated for usable energy values using young rats as the test model. The net increase observed in their carcass energy due to bulking agents fed over a 3-wk period was evaluated. Wheat fiber contained 0.9, polydextrose 0.8, isomalt 1.6, and oligofructose 1.5 calories/g. As a partial substitute for sugar, fat and/or flour, these bulking agents could effectively reduce the energy content of foods.