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Non-starch polysaccharides (NSP) show low digestibility in pigs and furthermore they negatively affect the digestibility of crude protein (CP) and several other nutrients. Fermentation of liquid feed and enzyme addition are promising strategies to increase the nutritional value of fibre-rich diets, while the combination of the two strategies until now is scarcely investigated. Hence the primary objectives of this Ph.D. thesis were: 1) to identify one or more enzyme mixtures able to disrupt the NSP fraction in RSC and DDGS during fermentation, and, as a consequence, solubilise the protein in the two ingredients; 2) to perform digestibility studies on grower pigs, investigating the digestibility of NSP, CP, phosphorus (P) and dry matter (DM), as affected by fermentation and concurrent addition of selected enzyme mixtures on a diet based on locally grown crops (HM M, RSC and peas) and on a diet based on DDGS.
Results showed that the enzyme mixture of β -glucanase + xylanase + pectinase (GluXylPec) showed significant reduction of total- and insoluble NSP during fermentation of RSC, along with increased concentration of soluble CP. In the diet based on locally grown ingredients both total-, insoluble- and soluble NSP were significantly reduced by addition of GluXylPec during fermentation. Fermentation alone improved apparent ileal digestibility (AID) of P and numerically improved AID of total-, insoluble- and soluble NSP, and apparent total tract digestibility (ATTD) of total- and insoluble NSP. Addition of GluXylPec fur ther improved these NSP parameters to significant levels. The in vitro fermentation study on DDGS showed potential of several enzyme mixtures to reduce total NSP during fermentation, the mixtures of xylanase + β -glucanase and cellulase + xylanase was chosen for digestibility experiments. Fermentation of the DDGS diet improved AID of NSP and ATTD of DM and P. Both enzyme treatments increased AID and ATTD of NSP compared to non-fermented liquid feed.
The overall conclusion is that the nutritional value of alternative diets with NSP-rich ingredients can be improved by fermentation and concurrent addition of NSP–degrading enzymes. This may be a strategy which in the future can increase the use of NSP-rich ingredients in diets for pigs.
Grethe Venås Jakobsen. Improving nutritional value of pig diets by fermentation and enzyme addition. PhD study at the Department of Animal Science, Aarhus University.