USE OF GUANIDINATED DIETARY-PROTEIN TO MEASURE LOSSES OF ENDOGENOUS AMINO-ACIDS IN POULTRY

Guanidinated proteins when fed to non-ruminants provide values for bot h endogenous amino acid losses and amino acid digestibilities, provide d that the homoarginine residues in the treated protein are randomly d istributed. Earlier studies have established that guanidination has on ly minor effects on the structure of the protein and, in particular, o n its susceptibility to proteolysis. Furthermore, we have confirmed th at homoarginine behaves as a typical amino acid in the small intestine . Lysine residues in casein and soya-bean protein, and in the proteins of cotton-seed meal, meat meal, soya-bean meal, maize, sorghum and wh eat were converted to homoarginine by guanidination, the extent of con version ranging from 37-68%. Sequential proteolysis in vitro of these guanidinated materials showed that the ratios of homoarginine to other amino acids remained unchanged for casein and soya-bean protein, indi cating random distribution of homoarginine residues, but not for all t he amino acids in meals and cereals. The use of guanidinated casein as the sole protein source in diets fed to broiler chickens allowed meas urement of endogenous losses of amino acids under normal feeding condi tions and calculation of true digestibilities of dietary amino acids a t the ileum. Endogenous amino acid losses measured by the use of guani dinated casein (15.3 g/kg dry matter (DM) intake) were significantly h igher (P < 0.001) than values obtained by feeding a N-free diet(5.4 g/ kg DM intake), or by regression analysis to zero N intake (7.2 g/kg DM intake).