Use of guanidinated dietary protein to measure losses of endogenous amino acids in poultry

Abstract

Guanidinated proteins when fed to non-ruminants provide values for both endogenous amino acid losses and amino acid digestibilities, provided that the homoarginine residues in the treated protein are randomly distributed. Earlier studies have established that guanidination has only minor effects on the structure of the protein and, in particular, on its susceptibility to proteolysis. Furthermore, we have confirmed that 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 wheat were converted to homoarginine by guanidination, the extent of conversion ranging from 37-68 %. Sequential proteolysis in vitvo of these guanidinated materials showed that the ratios of homoarginine to other amino acids remained unchanged for casein and soya-bean protein, indicating random distribution of homoarginine residues, but not for all the amino acids in meals and cereals. The use of guanidinated casein as the sole protein source in diets fed to broiler chickens allowed measurement of endogenous losses of amino acids under normal feeding conditions and calculation of true digestibilities of dietary amino acids at the ileum. Endogenous amino acid losses measured by the use of guanidinated casein (15.3 g/kg dry matter (DM) intake) were significantly higher (P c 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).Endogenous amino acids: Amino acid digestibility : Homoarginine: Guanidination: Poultry

Effects of wheat pentosans on endogenous amino acid losses in chickens

“…Lysine residues are converted into homoarginine under conditions which have negligible effects on the digestibility of the protein (Schmitz et a1 1991). Guanidination of casein occurs randomly, and homoarginine has been shown to behave in the small intestine like a typical amino acid (Siriwan et al 1994). The apparent ready conversion of homoarginine to lysine in tissues, however, precludes re-entry of homoarginine into the small intestine.…”

“…These considerations imply that the digestibility of homoarginine is identical to that of the other amino acids in guanidinated casein. Furthermore, comparison of the ratios of homoarginine to the other amino acids in guanidinated casein (the sole source of dietary protein) and ileal digesta, allows calculation of endogeneous amino acid losses (Siriwan et al 1994). In the present studies the homoarginine technique has been used to measure the effects of wheat pentosans, cellulose (Solka-Floc) and an inert nutrient diluent (Alkathene) in broiler diets on endogenous amino acid losses.…”

Amino acid digestibility and poultry feed formulation: expression, limitations and application

“…We have used both the protein free diet and the regression analysis method to measure the entry of endogenous amino acids into the lower ileum of broilers and roosters and have shown that the two methods give different results that vary with the maturity of the bird. We have compared these techniques to the homoarginine method and have shown that both techniques significantly underestimate endogenous amino acid secretion when compared with the latter technique (Siriwan et al, 1994). Bryden et al (1996) and Ravindran & Bryden (1999a) have discussed in detail the assumptions that are used when applying the homoarginine technique and these assumptions have been shown to be valid when tested.…”

Variation in seed protein digestion of different pea (Pisum sativum L.) genotypes by cecectomized broiler chickens: 1. Endogenous amino acid losses, true digestibility and in vitro hydrolysis of proteins

“…However, these methods only estimate basal endogenous losses, whereas specific endogenous losses which originate from the diet itself are not estimated. In order to assess the effect of diet on total endogenous losses (basal and specific), other methods have been developed such as labelling of lysine into homoarginine (Siriwan et al, 1994) or labelling of the diet with 15 N (Mahé et al, 1994;Hess et al, 2000). This last method is the only one which allows the determination of endogenous flow of each amino acid.…”