[Methodologic studies on the metabolism-oriented determination of methionine requirements of broiler chickens]

In a preliminary experiment the time course of 35S-excretion following a single injection of 35S-methionine in male broiler chickens was measured for 5 days. Within 2 days 65 to 69% of the amount of 35S excreted during the whole 5-day-period were recovered. Therefore, in the main experiment excrements for 35S measurement were collected only 2 days. During the main experiment starting 7 days posthatching 48 male broiler chickens received diets based on peas and wheat. The basal diet was supplemented with DL-methionine at 8 levels increasing the methionine content from 3.3 to 7.5 g/kg DM or 1,51 to 3.42 g/16 g N and the content of sulphur containing amino acids varied from 6.8 to 11.8 g/kg DM or 3.11 to 5.02 g/16 g N, respectively. Daily body weight gain was followed up to day 30 posthatching and N-balance was estimated during the 21st to 26th day posthatching. Up to day 26 a methionine content of 3.9 g/kg DM was sufficient for maximum weight gain. However, during the last period of the experiment highest weight gains were observed in animals receiving diets with 4.5 or more methionine/kg DM. Highest N-retention (1.2 g N/d) was measured if the diet contained 3.9 g methionine/kg DM or more. At day 28 posthatching 35S-methionine was injected intravenously and the subsequent 35S-excretion was measured. The 35S-excretion started to increase at a methionine content in the diet of 4.5 g/kg DM and continued to rise up to the highest methionine content of 7.5 g/kg DM. The metabolism oriented methionine requirement determination indicates for male broiler chickens at the beginning of the 5th week posthatching a methionine requirement of 3.9 to 4.5 g/kg DM (1.78 to 2.05 g/16 g N) and a requirement of S-containing amino acids of 7.4 to 8.0 g/kg DM (3.38 to 3.65 g/16 g N). The method used is potential in studying the age-dependent changes in methionine requirement.