The effect of tannic acid on the excretion of endogenous methionine, histidine and lysine with broilers

Tannins are a complex mixture of higher plant, water-soluble polyphenolic compounds of varying molecular masses that have the ability to react with proteins, polysaccharides and other macromolecules. Dietary tannins are thought to reduce the digestibility and metabolisable energy of feeds through direct interaction with proteins and carbohydrates from both exogenous and endogenous sources. In an experiment, sixty-four, 10-week-old broiler cockerels, in eight treatments of eight replicates, were fed warm glucose solution (30 g/50 ml, 40 °C) or water (50 ml) alone or with TA solution (3, 6, and 10 g/15 ml) by an oral gavage. Excreta voided from each bird following precision feeding, was collected quantitatively, for 48 h. The estimated amino acids in the excreta by HPLC showed an increase (P<0.001) in the endogenous losses of individual amino acids by tannic acid. The amino acids most affected were methionine (4.6-fold), histidine (4.8-fold), and lysine (4.3-fold) and the least affected amino acids were threonine (2.4-fold), cysteine (2.5-fold), and valine (2.4-fold) when the maximum amount of TA (10 g) was administered. There was no difference in the slope of the excretion of individual amino acids between glucose- and water-fed birds when the amount of TA increased. The possible mechanisms by which tannic acid increased linearly the loss of individual amino acids with endogenous origin are discussed.