Improving fiber utilization from rapeseed and sunflower seed meals to substitute soybean meal in pig and chicken diets: A review

Locally produced rapeseed meal (RSM) and sunflower seed meal (SFM) are preeminent alternatives in monogastric feed to reduce the reliance of the European Union (EU) on soy imports. However, RSM and SFM have greater fiber contents compared with soybean meal (SBM). Currently, the lack of information on the composition of RSM and SFM fibers, their degradation and influence on digestive processes hampers accurate prediction of their nutritional value when included in pig and poultry diets, and limits the development of strategies to enhance RSM and SFM fiber degradation. This review emphasizes the diversity of fibers, found in RSM, SFM and SBM, identifies recalcitrant non-starch polysaccharides (NSP) of these meals in monogastric animals, and indicates opportunities to improve degradation of these fibers. In pigs, undegraded NSP from RSM represent ~65 g/kg dry matter (DM), due to the limited degradation of uronyl-rich polysaccharides (0.50) and cellulose (0.66). SFM has the highest recalcitrant NSP content (~147 g/kg DM), because of poor degradation of xylosyl-rich polysaccharides (0.25) and cellulose (0.38). SBM has the lowest recalcitrant NSP content (~39 g/kg DM), mainly limited by degradation of cellulose (0.57), non-cellulosic glucosyl (0.53) and xylosyl-rich polysaccharides (0.61–0.65). In chickens, undegraded NSP represent ~165 g/kg DM for SBM and ~197 g/kg DM for RSM. Even the degradation of soluble fiber is often not complete. Substantial improvements in fiber degradation can be achieved using technologies targeting ingredient-specific recalcitrant fibers, potentially increasing energy yield from the meals by fermentation, and releasing encapsulated nutrients. For example, multi-carbohydrase addition improved degradation of RSM fibers in chickens by 113%, and in an in vitro pig model by 122%. In another study, cellulases improved RSM fiber degradation in an in sacco pig model by ~35%. Typically, synergistic effects between pectinases and (hemi)cellulases are seen, as expected from the complex cell-wall structures found in RSM and SFM. Modifying fibers from RSM and SBM using mechanical, (hydro)thermal, or chemical treatments is less successful (0–20%), due the recalcitrant nature of the fibers and the drastic conditions required. So far, only alkali treatment substantially improved degradation of RSM fibers (~48%) in an in sacco pig model. In conclusion, RSM and particularly SFM have a greater recalcitrant fiber content than SBM. To improve degradation of their fibers, technologies targeting cellulose from RSM and SFM, uronyl-rich polysaccharides from RSM, and xylosyl-rich polysaccharides from SFM seem essential. To that end, multi-carbohydrases including esterase activity, alkali-, or ligninolytic treatments, should be considered.