Influence of inoculum type (ileal, caecal and faecal) on the in vitro fermentation of different sources of carbohydrates in rabbits

Abstract

<p>Two <em>in vitro</em> experiments were performed to analyse the fermentative potential of ileal content, caecal content, soft faeces and hard faeces from adult rabbits. Experiment 1 evaluated 3 doses (0.5, 1.0 and 2.0 g fresh digesta/g substrate dry matter [DM]) of ileal and caecal digesta as inoculum in 28 h-incubations. Two ileal and 2 caecal inocula were obtained, each by pooling the ileal or caecal digesta of 2 adult rabbits. Pectin from sugar beet pulp (SBP) and the insoluble residue obtained after a 2-step <em>in vitro</em> pre-digestion of SBP and wheat straw were used as substrates. The 0.5 dose produced the lowest (<em>P</em><0.05) amount of gas at 28 h, with no differences (<em>P</em>>0.05) between the 1.0 and 2.0 doses (44.9, 51.6 and 53.8 mL/g substrate DM, respectively; values averaged across inocula and substrates). Experiment 2 evaluated two doses of ileal inoculum (1 and 1.5 g fresh digesta/g substrate DM) and compared ileal digesta, caecal digesta, soft faeces and hard faeces as inoculum for determining <em>in vitro</em> gas production (144-h incubations) of the 3 substrates used in Experiment 1 and wheat starch. Three inocula of each type were obtained, each by pooling either digesta or faeces from 3 rabbits. There were no differences (<em>P</em>>0.05) between the 2 ileal doses tested in gas production parameters, and therefore the 1.0 dose was selected for further ileal fermentations. Starch and pectin showed similar (<em>P</em>>0.05) values of gas production rate and maximal gas production rate when they were fermented with caecal digesta (0.038 vs. 0.043%/h, and 13.7 vs. 15.2 mL/h, respectively), soft (0.022 vs. 0.031%/h, and 9.97 vs. 9.33 mL/h) and hard faeces (0.031 vs. 0.038%/h, and 13.6 vs. 10.8 mL/h), and values were higher than those for SBP and wheat straw; in contrast, values for starch and pectin differed with the ileal inoculum (0.046 vs. 0.024%/h, and 18.4 vs. 6.60 mL/h). Both ileal and caecal gas production parameters were well correlated with those for hard and soft faeces inocula, respectively (r≥0.77; <em>P</em>≤0.040). The ileal inoculum showed a relevant fermentative potential, but lower than that of caecal digesta and soft and hard faeces for all substrates except wheat starch.</p>