3.3. Summary
Overall, these two techniques are attractive to determine total endogenous flows in animals that are in a physiologically normal state, following the feeding of wide range of protein sources. Both, however, suffer from practical limitations. Both are tedious, time-consuming and costly. Isotope dilution techniques, in particular, require highly specialised personnel, equipment and facilities. However, estimates from the isotope marker approach provide direct information only of the endogenous flow of one amino acid − leucine in most cases of isotopes; the flow of other amino acids are then calculated assuming a constant composition of endogenous protein, but this assumption may not be valid for specific losses since different anti-nutrients and fibre sources have different effects on the individual components of endogenous protein. On the other hand, in the case of guanidination method, the endogenous flow of all amino acids can be estimated; the deviation of the ratio of amino acid to HA in the ileal digesta from that in the diet for each amino acid is used to generate endogenous flow for each amino acid.