Effect of pig faecal donor and of pig diet composition on in vitro fermentation of sugar beet pulp

Two experiments were undertaken to investigate the influence of (1) pig bodyweight and (2) dietary fibre content of the diet on the in vitro gas production of sugar beet pulp fibre using faecal inoculum. In the first experiment, inocula prepared from young pigs (Y; 16-50 kg), growing pigs (G; 62-93 kg) and sows (S; 216-240 kg) were compared. Sugar beet pulp, hydrolysed in vitro with pepsin and then pancreatin, was used as the fermentation substrate. The cumulated gas productions over 144h were modelled and the kinetics parameters compared. Lag times (Y: 4.6h; G: 6.4h; S: 9.2h) and half-times to asymptote (Y: 14.7h; G: 15.9h; S: 20.8h) increased with pig bodyweight (P < 0.001) and the fractional degradation rates of the substrate differed between the pig categories (Y: 0.110 h(-1); G: 0.115 h(-1); S: 0.100 h(-1); P < 0.001). The final gas production was not affected (P=0.10) by the inoculum Source. In the second experiment hydrolysed sugar beet pulp was fermented with four inocula prepared from pigs fed diets differing in their total and soluble dietary fibre contents, i.e. low fibre diet rich in soluble fibre (LOW-S) or in insoluble fibre (LOW-I) or high fibre diet rich in soluble fibre (HIGHS) or in insoluble fibre (HIGH-I). The total and the soluble dietary fibres influenced the kinetics of gas production. The presence of soluble fibres decreased the lag times, whatever the total dietary fibre content (2.7 h for LOW-S versus 3.5 h for LOW-I, 4.0 h for HIGH-S versus 4.4 h for HIGH-I; P < 0.001). The half-times to asymptote were higher with the low fibre diets (P < 0.001) and, for similar total dietary fibre contents, they were lower when the proportion of soluble fibres increased (LOW-S: 9.9 h; LOW-I: 11.4 h; HIGH-S: 8.9 h; HIGH-I: 10.1 h; P < 0.001). The fractional degradation rates of the substrate were the highest with the fibre-rich diet containing a high proportion of soluble fibres (0.158 h(-1); P < 0.001). In conclusion, the bodyweight of the faeces donors and the dietary fibre composition of the pig diet influence the in vitro fermentation kinetics of hydrolysed sugar beet pulp, but not the final gas production. (c) 2006 Elsevier B.V. All rights reserved.