THE MEASUREMENT OF ENDOGENOUS AMINO-ACIDS IN THE EXCRETA OF ADULT COCKERELS

Different methods of determination of endogenous amino acid output in the excreta of intact and caecectomised cockerels were evaluated in th ree experiments. In Experiment 1, comparison was made between excreta endogenous amino acid outputs determined by the use of protein-free di ets and by regression analysis in adult cockerels fed on semi-purified diets containing graded levels of protein (50 to 250 g/kg) from eithe r soyabean meal or cottonseed meal. In both diet types, the excreta en dogenous amino acid levels in birds fed a protein-free diet were highe r than those determined by the regression method. Caecectomy had no in fluence (P > 0.05) on endogenous amino acid losses in the excreta when determined by the protein-free diet method. A similar trend was obser ved for estimates from regression analysis, although differences were noted for some amino acids between intact and caecectomised cockerels. In experiment 2, excreta amino acid outputs were determined after a 2 4-h fast. Endogenous amino acid flows in fasted intact birds were high er (P < 0.05) than those from caecectomised birds. The largest differe nces were observed for asp, glu, val, leu, arg, thr and ala. The total endogenous amino acid output in caecectomised birds following the fas t was non-significantly (P > 0.05) lower than those determined after f eeding the protein-free diets, but higher than the estimates determine d by the regression method. In experiment 3, the possibility of using the recently developed homoarginine method to determine endogenous ami no acid outputs in the excreta was evaluated. However, application of this technique to excreta analysis resulted in aberrant endogenous ami no acid values due to the unexpectedly high homoarginine values found in excreta. These results indicate that homoarginine is not a suitable marker to estimate endogenous amino acid losses in excreta.