Preliminary evaluation of fenugreek (Trigonella foenum-graecum) seed gum as a potential prebiotic for growing rabbits in Tunisia: effects on in vivo faecal digestibility and in vitro fermentation

This study aims to determine the effect of dietary inclusion of fenugreek seed gum (FSG), rich in galactomannans, on nutrient apparent digestibility and caecal environment, as well as on in vitro caecal fermentation of Tunisian growing rabbits. Three experimental diets were formulated, including 0, 0.25 and 0.5% of FSG(FSGO, FSGO.25 and FSGO.5, respectively) for the in vivo trial and 0, 0.125, 0.25, 0.5 and 100% of FSG (FSGO, FSG0125, FSGO.25, FSGO.5 and FSG1 00, respectively) for the in vitro trial. In the in vivo trial, 45 weaned rabbits 31 d old (15 per treatment) were housed in individual cages until 94 d of age. Apparent digestibility coefficients were determined at two ages, from 38 to 41 and from 56 to 59 d old, and caecal traits were recorded after slaughtering. In the in vitro trial, the five experimental diets were incubated with a rabbit caecal inoculum. Gas production was measured and modelled until 72 h and the fermentation traits were measured. Apparent faecal digestibility coefficients of main nutrients and main caecal environment traits were not significantly affected by the dietary inclusion of FSG(P>0.05). However, animals fed with FSG showed lower caecal pH (-0.15; P<0.05) values. Regarding the in vitro fermentation, FSG100 increased asymptotic gas production (+11.25, P<0.001), sharpness of the switching characteristic of the profile (+1.98, P<0.001) and the maximum substrate degradation rate (RM) (+0.188, P<0.001), but decreasing the time after incubation at which half of the asymptotic amount of gas has been formed (-5.86, P<0.001) and at which RM occurs (-4.53, P<0.01). Likewise, FSG1 00 significantly decreased caecal pH (-1.035, P<0.001), lactic acid (-9.51, P<0.069) and N-NH3 concentrations (-12.81, P<0.001). Meanwhile, it increased the total volatile fatty acids (VFA) production (+43.15, P<0.001). Gradual dietary inclusion of FSG from 0 to 0.5% only significantly increased total VFA production in the caecum (+100 mmol/L per percentage point of FSG inclusion; P<0.05). In conclusion, FSG is highly and rapidly in vitro fermented by rabbit caecal bacteria. However, dietary inclusion of FSG up to 0.5%, might be insufficient to affect the apparent digestibility and fermentation profile of growing rabbits to a great extent.