NUTRITIONAL SIGNIFICANCE OF ENDOGENOUS N-LOSSES ALONG THE GASTROINTESTINAL-TRACT OF FARM-ANIMALS

In animal production, endogenous protein losses associated with the di gestion process are important losses, but difficult to measure. Measur ing methods include feeding N-free diets, regression techniques based on amino acid profiles, and separating feed protein and endogenous pro tein by markers like homoarginine, hydrolysed casein or stable isotope s like N-15. Endogenous losses arise from saliva, digestive enzymes, b ile, shedded epithelial cells and mucins and may be extra stimulated b y the presence in feeds of antinutritional factors (ANF) such as lecti ns, trypsin inhibitors (TI), tannins and fibre. The impact of such fac tors may differ between non-ruminants and ruminants. The magnitude of the effect of the different factors is quantified and some of the cons equences for protein deposition and nitrogen losses to the environment are discussed.