The influence of soluble and insoluble lupin non-starch polysaccharides on the digestibility of diets fed to rainbow trout (Oncorhynchus mykiss)

This study examined the effect of increasing inclusion levels of soluble and insoluble lupin (Lupinus angustifolius) fibres, and purified cellulose on the dry matter, protein and energy digestibility of diets fed to rainbow trout (Oncorhynchus mykiss). Soluble and insoluble fibre fractions from lupin kernel meal were produced using differential pH solubilities. There were significant differences among the digestibility parameters of the diets with different inclusion levels of each of the different fibre types, except for the soluble lupin fibre, which had limited effect on any digestibility parameters. Differences among diets in dry matter and energy digestibility were most distinct. Using an ANOVA analysis no significant differences were noted for diet protein digestibilities with any of the fibre types. However, regression analysis of the effect of fibre inclusion levels showed significant effects on all digestibility parameters, including protein digestibilities. The lupin insoluble NSP also had a greater effect on dry matter and energy digestibilities than that of cellulose, with findings suggesting that it also affected the digestibility of additional nutrients in the diet to a degree not seen with cellulose. These results show that different fibre classes can have distinctly different effects on diet digestibility parameters.