[Methodological studies of the metabolism-oriented determination of the lysine requirement in broiler chickens. 1. Influence of the lysine content of the diet on the lysine oxidation rate in short-term food withdrawal before 14C-lysine injection].

For the estimation of lysine requirement 128 male broiler chickens were used at an age of 7 to 21 days posthatching. They received a lysine deficient diet composed of wheat and wheat gluten. To this basal diet L-lysine-HCL was supplemented successively resulting in 8 lysine levels ranging from 5.8 to 23.3 g lysine per kg DM (2.2 to 8.7 g lysine per 16 g N). At the end of the two-week feeding period of the experimental diets 14C-lysine was injected intravenously 1.5 and 5.5 hours after feed withdrawal. During the following 4 hours the excretion of CO2 and 14CO2 was measured. This 4 hours absorption period for 14CO2 was regarded as sufficient according to a preliminary experiment. The highest daily gain of 21.5 g was observed in animals fed 13.3 g lysine/kg DM. Lysine concentrations exceeding 18.3 g/kg DM depressed body weight gain. The CO2-excretion was not influenced by lysine intake. The 14CO2-excretion was low with diets low in lysine content and increased 3 to 4 times with diets meeting the lysine requirement. Based on measurements 1.5 to 5.5 hours after feed withdrawal the saturation value for lysine was reached at 13.3 g/kg DM. This value was lowered (10.8 g/kg DM), however, if the estimation was carried out 5.5 to 9.5 hours after feed withdrawal. These results suggest a higher metabolic lysine requirement during the earlier period after feed intake. Both, reduced weight gain and non linearity in 14CO2-excretion with diets exceeding a lysine content of 18.3 g/kg DM indicate a limited capacity of the organism to degrade excessive lysine. According to the results of this experiment for broiler chickens 3 weeks posthatching a lysine requirement between 10.8 and 13.3 g/kg DM (27% CP and 660 EFUhen/kg DM) was concluded. The range of estimated requirement data could be narrowed by the use of diet with other lysine content.