The effect of genotype and dietary fibre level on the caecal bacterial enzyme activity of young piglets: digestive consequences

The effect of genotype and dietary fibre level on the coefficient of total tract apparent digestibility (CTTAD) and dry matter (DM), pH, ammonia–nitrogen (N–NH3), short chain fatty acids (SCFA) and microbial enzyme activity, in the caecal contents, of young piglets, was studied using 16 Alentejano (AL) and 16 Duroc×Landrace (D×LD) piglets, aged 35 days. Piglets of each genotype, were distributed in two groups of eight animals housed individually and received on a pair feeding basis, one of the two experimental diets. The diets were formulated to contain 100 or 170 g NDF kg−1 by partial replacement of wheat by wheat bran. The piglets were individually controlled during 4 successive weeks and faeces were collected during the first and the last week for digestibility measurements. At the end of the experimental period, all piglets were slaughtered and the caecal contents collected. TAD of NDF was 0.64 and 0.54 (P<0.001) and that of ADF was 0.58 and 0.37 (P<0.001) for AL and D×LD piglets, respectively. Excepting CP and minerals, the increase of the fibre level significantly decreased the CTTAD of dietary constituents. The total xylanolytic activity was 22.0 and 13.6 (mg h−1 g−1 of fresh caecal contents) and the total cellulolytic activity was 24.7 and 12.6 (mg h−1 g−1 of fresh caecal contents) for AL and D×LD piglets, respectively (P<0.10). The acetic:propionic ratio (C2:C3) was significantly higher in the caecal contents of AL piglets. However in D×LD piglets the proportion of propionic acid (C3) was higher (P<0.01). The fibre level had no significant effect on total and specific activity of amylase, xylanase, pectinase and cellulase in the caecum. The concentration and profile of SCFA and the level of N–NH3 in caecal contents was not significantly affected by the dietary fibre level. In conclusion, the higher digestive capacity of AL piglets towards the non-starch polysaccharides seems to be related to a better adaptation of the enzymatic activity i.e. xylanase and cellulase of the caecal microflora to degrade the cell wall constituents of the diet.