Digestion of plant cell walls from four different sources in growing pigs

Large White pigs of about 40 kg were grown on six diets (4 pigs per diet) that contained 40% wheat and soya bean protein as protein source. In the control diet (W) the only added carbohydrate source was starch; in the five other diets this was partly replaced by 22% wheat bran (WB), 44% wheat bran (2WB), 16% sugar beet pulp (SBP), 19% soya bean hulls (SBH) or 22% wheat straw (WS). The animals were given similar amounts of digestible energy. The apparent digestibility (AD) of dry matter (DM), nitrogen (N), energy (E), neutral detergent fibre (NDF), acid detergent fibre (ADF) and non-starch polysaccharides (NSP) of the diets was determined. Whatever the fibre source added to the diets, the AD of N and E was significantly reduced relative to the control diet. In diets with similar NSP contents (2WB, SBP, SBH, WS diets), the AD of E was higher in SBP and SBH diets (0.841 and 0.834 for E, respectively) and lower in the WS diet (0.736). No significant change in AD of N (0.810 on average) was observed. The AD of NDF varied with that of total NSP (WS < 2WB < WB < SBP < SBH) but with lower values for AD of NDF. Increasing the amounts of wheat bran in diets reduced total NSP and ADF digestibility. In diets with similar amounts of NSP, plant cell walls from SBP and SBH diets were highly digestible (0.692 and 0.745 for total NSP, respectively) while those from the WS diet were the least degraded (0.298), the AD of total NSP from the 2WB diet being intermediate (0.508).