[Hot weather damage of wheat gluten: determination of the intermediate lysine degradation in chicks using isotope techniques (14C-U-L-lysine oxidation].

The aim of our experiments was to identify a restricted lysine bioavailability after heating of wheat gluten by estimating a reduced metabolic 14C-lysine degradation. In two trials, male broiler chickens were fed with six diets based on wheat and wheat gluten (gluten untreated or heated), but differing in lysine content according to lysine supplementation. In trial 1 animals were fed restrictively, in trial 2 they were fed ad libitum. For estimation of metabolic lysine degradation all animals received an additional i.v. injection of 14C-U-L-lysine 3 weeks posthatching, followed by hourly collection of 14CO2 up to 3 h after injection. There were no differences between groups receiving untreated or heated gluten concerning weight gain and N-balance if the lysine supplementation was medium or high. When applying a lysine supply close to the requirement level or above the requirement the lysine degradation to 14CO2 (% of the dose) and the specific radioactivity of CO2 in animals receiving heated gluten was significantly lower compared to the corresponding group with untreated gluten. It can be concluded that reduced bioavailability of lysine due to heat treatment of gluten might be indicated by means of weight gain or N-balance only at lysine supply levels below the requirement. In contrast, measurements of lysine degradation by means of 14CO2-excretion after i.v. lysine injection indicate the heat-damaging effect, especially at lysine levels close to the requirement.