World Rabbit Science (Sep 2018)
Influence of inoculum type (ileal, caecal and faecal) on the in vitro fermentation of different sources of carbohydrates in rabbits
Abstract
Two in vitro 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 in vitro pre-digestion of SBP and wheat straw were used as substrates. The 0.5 dose produced the lowest (P0.05) 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 in vitro 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 (P>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 (P>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; P≤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.
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