Non-digestible oligosaccharides (NDOs), including fructo-oligosaccharides (FOS) and trans-galacto-oligosaccharides (TOS), are not digested by endogenous enzymes, but may be fermented by bacteria such as lactobacilli and bifidobacteria (Tomomatsu, 1994). Thus, dietary NDOs may alter fermentation characteristics of the microflora of the host. In this experiment, in vivo and in vitro fermentation characteristics of NDOs in weaner pigs were studied, using the cumulative gas production technique (Theodorou et al.,1994).

A NDO-free control diet (CON), with oatshuskmeal (OHM) as a fibre source, and this diet with 40 g FOS (FOS40) or TOS (TOS40) per kg (w/w against cellulose) was restrictedly fed for 7 weeks (2.6*Em) to 3 groups of four 35-day old individually housed weaner pigs. Total faeces were collected from day 13-18 to determine crude fibre digestibility. Pigs were fitted with a PVTC-cannula on day 21 (Van Leeuwen et al, 1991). Inocula for gas production were anaerobically prepared from faeces (day 14-16) and ileal chyme (day 33-35, via PVTC-cannula). Samples were diluted (1:4) with sterile saline and filtered through cheese cloth. Five ml filtrate were injected into airtight bottles, containing 80 ml growth medium and no substrate (BLA) or 0.25 g FOS, TOS or OHM as sole energy source.