EVALUATION OF HOMOARGININE AS A MARKER FOR THE DETERMINATION OF ENDOGENOUS AMINO-ACID-CONCENTRATIONS IN POULTRY EXCRETA

1. Endogenous amino acid losses in ileal digesta and excreta of adult cockerels fed on diets containing guanidinated forms of casein, soyabe an meal and cottonseed meal were determined using homoarginine as a ma rker. 2. The ileal endogenous amino acid losses were markedly higher ( P<0.001) in birds given the cottonseed meal diet compared to those giv en the other two diets. The ileal endogenous protein was rich in aspar tic acid, serine and glutamic acid. 3. Negative values were obtained f or endogenous amino acid output in excreta. These aberrant values were caused by high concentrations of homoarginine in the excreta. A subse quent study with broiler chickens showed that the homoarginine in excr eta was of urinary origin. 4. These results indicate that the homoargi nine technique is not suitable for determining endogenous amino acid l osses in excreta, but applicable when determinations are made in the t erminal ileum.