PREDICTION OF THE APPARENT ILEAL DIGESTIBILITY OF PROTEIN AND AMINO-ACIDS IN FEEDSTUFFS AND FEED MIXTURES FOR PIGS BY IN-VITRO ANALYSES

An in vitro method for the prediction of protein and amino acid digest ibility at ileal level is described. Values of in vitro digestibility of protein in 15 common feedstuffs were an higher than corresponding v alues of apparent ileal digestibility. The difference is suggested to correspond to endogenous protein losses (EPL). A close relationship be tween EPL and in vitro undigested dry matter (UDM) was demonstrated: E PL, g kg(-1) DM intake=13.2+0.066 X UDM, g kg(-1) DM (n=15; r(2)=0.61; RSD=4.5; CV=17.1). The prediction of apparent ileal digestibility of protein (pdN(ileal)) by using the equation: pdN(ileal), %=dN(in vitro) , %-100 X (13.2+0.066 X UDM, g kg(-1) DM)/Protein-(feed), g kg(-1) DM, was highly related to the in vivo determined ileal digestibility of p rotein (r(2)=0.92; RSD=3.5; CV=4.9) in the same 15 feedstuffs. The met hod was validated with 48 feed mixtures with known in vivo digestibili ty. The relationship was considerably lower (r(2)=0.57), which was par tly due to the narrow variation range in protein digestibility in vivo . The in vitro digestibility of amino acids (measured in nine feedstuf fs) was in general closely related to that of protein. Exceptions were cystine, arginine, aspartic acid, glutamic acid and proline. The endo genous losses of the individual amino acids were calculated in a simil ar way as described for EPL. The resulting amino acid composition of t he endogenous protein was very close to reported values in the literat ure based on direct measurements in vivo. Apparent ileal digestibility of the individual amino acids was predicted in a similar way as descr ibed for protein. The relationship was generally higher for essential amino acids, and generally lower for non-essential amino acids, than f or protein (e.g. r(2) values of 0.65, 0.71 and 0.77 was obtained for l ysine, leucine and isoleucine, respectively, but 0.34 and 0.14 for glu tamic acid and proline, respectively). The described in vitro approach for protein evaluation seems to have a significant potential for prac tical purposes.