Evaluation of an in vitro system to simulate equine foregut digestion and the influence of acidity on protein and fructan degradation in the horse′s stomach

Abstract

SummaryThe aim of this study was to improve an in vitro system in order to gather optimized information on the digestion of different forages in the horse 0 s upper gastrointestinal tract. Therefore, foregut digestion of several forages was simulated in vitro (Part 1). The effect of different pH values on in vitro fructan degradation of two selected grasses (Part 2) was tested subsequently. Part 1: We hypothesized that our system produces representative results simulating digestive processes in the upper alimentary tract, but neglects microbial fermentation. In vitro digestion of six forages (grass mixture for horses, grass mixture for cows (GMC), tall fescue, English perennial ryegrass (ER), white clover, lucerne) was performed in two phases with pepsin and pancreatin. The results are consistent with current data from in vivo studies, including a degradation of crude protein and monosaccharides as well as a relative increase in fibres. Interestingly, a loss of fructan was measured in two feedstuffs (ER/GMC: 4.1/4.4% DM fructan before and 0.59/0.00% DM after simulated foregut digestion). Part 2: As fructans are thought not to be fragmented by digestive enzymes, another hypothesis was developed: acidic hydrolysis leads to a degradation of fructans. To evaluate the influence of gastric pH on the digestion of fructan and protein, different pH values (2, 3 and 4) were adjusted in a second series of in vitro foregut digestion trials with ER and GMC. As expected, the highest degradation of protein was seen at the lowest pH (protein in ER/GMC at pH 2: 6.11/8.28% DM and at pH 4: 7.73/10.64% DM), whereas fructan degradation was highest at pH 4 (fructan in ER/GMC at pH 2: 1.63/1.95% DM and at pH 4: 1.31/0.91% DM). We presume that not only acidic hydrolysis but also plant enzymes cause the loss of fructans in an acidic environment.

Modification of the equine gastrointestinal microbiota by Jerusalem artichoke meal supplementation

“…This finding is in accordance with other studies that also described the fermentation of inulin and/or grass fructans starting in the lower gut [20, 40]. The degradation might possibly be started by acid hydrolysis in the stomach [23, 24]. Furthermore, the WSC content in the large intestine was zero in the current study, indicating a largely complete degradation in the foregut.…”

“…Hitherto, some authors speculated from in vivo or ex vivo results that the fermentation of inulin-type fructans, as well as inulin itself, begins in the foregut [20, 21] and particularly the stomach [21], which might cause negative effects concerning stomach health. In vitro studies support the suggestion that the digestion of fructans in particular (in terms of acid hydrolysis) might not occur in the large intestine alone (as previously assumed) [22, 23, 24]. Consequently, we hypothesized that i) the feeding of FOS + inulin as active prebiotic ingredients originating from Jerusalem artichoke meal has an impact on the microbiota of the entire GIT and that ii) prebiotic compounds act as possible substrates for the microbiota in the stomach.…”

Glycaemic and insulinaemic responses of adult healthy warm‐blooded mares following feeding with Jerusalem artichoke meal

“…(), Ince et al. () and Strauch et al (), fructans are prone to be already decomposed in the lower gut, including the stomach where the DP might be of particular importance (Strauch et al, ). Glatter et al.…”

“…Previously, PP exhalation of methane and hydrogen in equines indicated that inulin started to be fermented already in the foregut (Coenen et al., ). In vitro studies with grass fructans suggested that under specific conditions, acid hydrolysis in the stomach leads to the decomposition of grass fructans (Ince et al., ; Strauch et al, ). When fructose is released and not immediately fermented by gut microbes, it might be absorbed in the equine digestive tract by specific transporters (Glut 5), which are highly abundant in the small intestine (Fernandez‐Castaño Merediz et al., ; Taylor et al, ), and is transported through the bloodstream into the liver.…”

Associative Effects between Forages and Concentrates on In Vitro Fermentation of Working Equine Diets

“…All the ingredients used for the experimental diets were treated with digestive enzymes using the in vitro method with the technique described by Strauch et al [ 28 ]. Briefly, each sample was performed in triplicates.…”