PREDICTION OF APPARENT ILEAL PROTEIN DIGESTIBILITY IN PIGS WITH A 2-STEP IN-VITRO METHOD

The use of a two-step in-vitro method to predict the in-vivo ileal digestibility of proteins in pigs was investigated. It proved not possible to predict accurately the ileal protein digestibility with the in-vitro method. By dividing the samples into groups of closely related products, a good relationship (r2 = 0.93) between in-vivo and in-vitro data was only obtained for wheat products, where only five samples were analysed. For beans, peas, rapeseed products and soya bean products it was still not possible to predict the in-vivo protein digestibility (r2 = 0.03-0.60). The in vivo-in vitro relationship was mainly determined by the properties of the proteins and the presence of antinutritional factors, such as lectins and trypsin inhibitors. The first influences both the in-vitro and in-vivo protein degradability and the latter only reduces the in-vivo degradability by stimulating the secretion of endogenous protein. It is suggested that, with the in-vitro method, real ileal digestibility of proteins is predicted. The apparent ileal protein digestibility can only be predicted with the in-vitro method after making corrections for the influence of these antinutritional factors on the secretion of endogenous protein. Possibly corrections are also needed for microbial protein, and protein which is solubilised in the small intestine but not absorbed because of the physical state of the chyme.