Effect of cellobiose supplementation and dietary soluble fibre content on in vitro caecal fermentation of carbohydrate-rich substrates in rabbits

Abstract

The in vitro caecal fermentation of five substrates low in starch and protein content [d-(+)-glucose (GLU), d-cellobiose (CEL), sugar beet pectin (PEC), sugar beet pulp (SBP) and wheat straw (WS)] was investigated using soft faeces from rabbits receiving different levels of cellobiose and soluble fibre as inoculum. A total of 24 rabbits were supplemented 3 levels of cellobiose in the drinking water (0.0, 7.5, 15.0 g/l) and fed two experimental diets containing either low soluble fibre (LSF) or high soluble fibre (HSF) levels (84.0 and 130 g/kg dry matter). All substrates were subjected to a two-step pepsin/pancreatin in vitro pre-digestion, and the whole residue was used as substrate for the in vitro incubations. Gas production was measured until 144 h, and volatile fatty acid (VFA) production was determined at 24 h incubation. Experimental treatments did not affect SBP fermentation and had only a subtle influence on fermentation of WS and GLU. In contrast, cellobiose supplementation × donors' diet interactions were detected for most gas production parameters for CEL. Both the fractional gas production (k) and maximal gas production rates were linearly increased (p ≤ 0.042) and the initial delay in the onset of gas production (Lag) linearly decreased (p < 0.001) by cellobiose supplementation with the HSF inoculum, with no differences between the 7.5 and 15.0 doses. In contrast, with the LSF inoculum cellobiose supplementation only affected k values, which were quadratically increased (p = 0.043) and had maximal values for the 7.5 dose. A quadratic effect (p ≤ 0.018) of cellobiose supplementation was observed for total VFA production at 24 h when CEL and PEC were fermented, obtaining the maximal VFA production for the 7.5 dose of cellobiose. Total VFA production for CEL was greater with LSF than with HSF inoculum (20.7 vs. 12.9 mmol/l; p = 0.014), but the opposite was found for WS (3.97 vs. 6.21 mmol/l; p = 0.005). The use of LSF inoculum for CEL fermentation sharply reduced acetate (p = 0.001) and increased butyrate proportions (p ≤ 0.001) compared with the HSF inoculum. A positive relationship between total VFA caecal concentrations in rabbits receiving the same experimental treatments and in vitro values was only observed when WS was used as substrate (r = 0.90; p = 0.015; n = 6). The results suggest that experimental factors influenced the fermentative activity of caecal digesta, but the observed response differed with the incubated substrate, being the CEL the most affected.

Effect of Dietary Insoluble and Soluble Fibre on Growth Performance, Digestibility, and Nitrogen, Energy, and Mineral Retention Efficiency in Growing Rabbits

“…The increase of SF when NDF is low (LIF-HSF vs. LIF-LSF) improved both NDF and SF digestibility in agreement with previous studies [7,9,23]. It is explained by the faster digestion rate of SF, similar to that observed in vitro for SBP when compared with straw [36]. The increase of NDF when SF is high (HIF-HSF vs. LIF-HSF) improved also the NDF and SF digestibility as expected [37,38] but the NDF to a lesser extent.…”

Characterisation and In Vitro Evaluation of Fenugreek (Trigonella foenum-graecum) Seed Gum as a Potential Prebiotic in Growing Rabbit Nutrition

“…FSG was highly fermented by rabbits’ caecal microflora because of its high carbohydrate content, which is positively correlated with the maximum cumulative volume of gas production [ 51 ]. The fermentative behaviour of FSG was similar to that shown by other soluble fibre sources in rabbits [ 52 , 53 ], having a maximum gas production rate (3.1 to 3.7 mL/h) between that of sugar beet pulp (2.9 mL/h) and that of pectin (6.0 to 8.0 mL/h). The high level of microbial fermentation of FSG might imply high energy losses, which may require a nitrogen source supplementation.…”

Effect of dietary soluble and insoluble fibre level, oligosaccharide supplementation and feed restriction on rabbit performance

“…LIF-LSF) improved both NDF and SF digestibility in agreement with previous studies (Trocino et al, 2013;Abad-Guamán, 2015;Delgado et al, 2019). It is explained by the faster digestion rate of SF, similar to that observed in vitro for SBP when compared with straw (Ocasio-Vega et al, 2018a). The increase of NDF when SF is high (HIF-HSF vs. LIF-HSF) impaired the NDF and SF digestibility that partially agreed with previous results (Caîsin et al, 2020;.…”

“…It would suggest that the dietary insoluble fibre level should be limited after weaning. The digestive symptoms during the trial pointed to ERE, but the most affected groups (HIF) showed an increase of caecal pH instead of the caecal acidification we found during ERE outbreaks (Gómez-Conde et al, 2007;Ocasio-Vega et al, 2018a), although this was not observed in other farms (Martínez-Vallespín et al, 2011). The highest caecal pH found in HIF-LSF group might be associated to its high ileal protein flow and a potential higher ammonia concentration in the caecum that would agree with the higher urinary nitrogen losses reported in Exp.…”

“…A positive effect of non-digestible oligosaccharides supplemented in drinking water on feed efficiency should be expected if feed intake is not affected, especially in diets with a high protein content, like those of this experiment. However, the effect of cellobiose supplementation in drinking water on feed efficiency was widely variable, from positive to even negative, depending on the dose, and the dietary level of SF (Ocasio-Vega et al, 2018a, 2018b. In broilers, the improvement of feed efficiency by XOS was accompanied by a parallel increase of villous height and changes in the caecal/colonic microbiota (De Maesschalck et al, 2015).…”