Dietary influences on endogenous ileal protein and amino acid loss in the pig - A review

The basis for using determined values of endogenous ileal protein and amino acid losses in the protein evaluation of pig feeds is reviewed. The amounts of endogenous protein and amino acids in ileal digesta may be determined by numerous methods. These include N-free diets, regression analysis, enzyme hydrolysed casein (EHC) coupled with ultra-filtration, modifying lysine to homoarginine, isotope dilution techniques and calculations based on the difference between the in vitro and in vivo digestibility of protein and amino acids. Endogenous ileal protein loss seems to be influenced primarily by dietary dry matter intake and secondarily by the composition of the diet and can be divided into a basal and an extra loss. The basal loss after ingestion of experimental N-free diets is 10-15 kg(-1) DM intake, but, under more physiologically normal conditions when protein-containing diets are ingested, the basal loss seems to be about 20 g kg(-1) DM intake. When vegetable feedstuffs are ingested there is often an extra loss specifically induced by the presence of dietary fibre and/or antinutritional factors (ANFs), resulting in total losses that are typically in the range of 20 to 40 g kg(-1) DM intake. The amino acid composition of endogenous protein is relatively constant for different diets and methods of determination and seems not to be influenced significantly by the amount of loss and liveweight of pig. For practical purposes, and lacking evidence to the contrary, the composition can be considered to be constant and the following general composition (g per 160 g N) of essential amino acids is proposed: lysine 30, methionine 10, cystine 16, threonine 45, tryptophan 12, isoleucine 25, leucine 40, histidine 15, phenylalanine 30, tyrosine 20, valine 35. The composition is, compared with ideal protein and most feedstuffs, characterized by a relatively low contribution of all essential amino acids, except threonine, cystine and tryptophan.