In vitro caecal fermentation of carbohydrate-rich feedstuffs in rabbits as affected by substrate pre-digestion and donors' diet

Abstract

The influence of substrate pre-digestion and donors' diet on in vitro caecal fermentation of different substrates in rabbits was investigated. Eight crossbreed rabbits were fed 2 experimental diets containing either low (LSF; 84.0 g/kg dry matter [DM]) or high soluble fibre (HSF; 130 g/kg DM) levels. In vitro incubations were conducted using batch cultures with soft faeces as inoculum and four fibrous or fibre-derived, lowstarch and low-protein substrates: D-cellobiose (CEL), sugar beet pectin (PEC), sugar beet pulp (SBP) and wheat straw (WS). Substrates in half of the cultures were subjected to a 2-step pepsin/pancreatin in vitro digestion without filtration, and the whole residue (soluble, insoluble and added enzymes) was incubated at 39°C. Gas production was measured until 144 h, and volatile fatty acid (VFA) production at 24 h incubation was determined. Cultures without substrate (blanks) were included to correct gas production values for gas released from endogenous substrates and added enzymes. Pre-digestion had no influence on in vitro gas production kinetic of WS, and only reduced the time before gas production begins (lag time; by 31%; P=0.042) for SBP, but for both substrates the pre-digestion decreased the molar proportion of acetate (by 9%; P≤0.003) and increased those of propionate and butyrate (P≤0.014). For CEL, the pre-digestion increased the gas and total VFA production (by 30 and 114%), shortened the lag time (by 32%), and only when it was combined with LSF inoculum 38 percentage units of acetate were replaced by butyrate (P≤0.039). Treatments had a minor influence on in vitro fermentation traits of SBP pectin. The results showed that the pre-digestion process influenced the in vitro caecal fermentation in rabbits, but the effects were influenced by donors' diet and the incubated substrate. Pre-digestion of substrate is recommended before conducting in vitro caecal fermentations. The level of soluble fibre in the donors' diet also influenced the in vitro caecal fermentation, but its effect depended on the type of substrate.

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

“…Samples (250 mg DM) of each substrate were carefully weighed into 115-ml glass vials and were subjected to a two-step pepsin-pancreatin in vitro digestion (pre-digestion) following the method of Ramos et al (1992), with the only exception that the contents of the vials were not filtrated at the end of the procedure. All vials were stored at 4°C overnight to stop the digestion process, and placed back in an incubator at 40°C for 1 h before starting the in vitro incubations (Ocasio-Vega et al 2018a). A total of 120 vials with substrate (3 cellobiose concentrations × 2 donors' diet × 5 substrates × 4 rabbits) and 24 vials without substrate (blanks; one per rabbit) were used.…”

“…Gas production values measured at each time and VFA values at 24 h were corrected for the amount of gas and VFA, respectively, produced in the corresponding blanks to correct for endogenous production (Ocasio-Vega et al 2018a). Gas production data were fitted to the logistic model described by Schofield et al (1994):…”

Marine Macroalgae in Rabbit Nutrition: In Vitro Digestibility, Caecal Fermentability, and Microbial Inhibitory Activity of Seven Macroalgae Species from Galicia (NW Spain)

“…Gas production values measured at each time and VFA values at 24 h were corrected for the amount of gas and VFA, respectively, produced in the corresponding blanks to discount the endogenous production from the caecal content used as inoculum [50]. Gas production data were analyzed using a mixed model for repeated measurements, including the sample, the time of measurement, and their interaction as fixed effects, and inoculum (donor rabbit) as a random effect.…”

“…The caecal inocula were obtained from rabbits that were not fed macroalgae, and the adaptation required would have delayed the beginning of the fermentation process. The need for substrate adaptation by the rabbit intestinal microbiota has been already observed when using a very specific substrate (cellobiose) [50].…”

“…This sample was used to analyze VFA production in the samples that yielded at 48 h of incubation significantly more gas production than the untreated cereal straw used as reference (gas production > 45 mL/g DM). Samples were processed as described by Ocassio-Vega et al [50] and VFA concentration was measured by gas chromatography [51] using a Pelkin Elmer Autosystem XL gas chromatograph (Perkin Elmer Inc., Shelton, CT, USA) equipped with an automatic injector, detector flame ionization, and a semi-capillary column (TR-FFAP 30 m × 0.53 mm × 1 µm; Supelco, Barcelona, Spain).…”