Efficiency of methionine and cystine utilization by broiler chickens using stable isotopes.

The aim of this study was to develop a method to determine the efficiency of utilization of Met and Cys using stable isotopes in order to reduce the number of sacrificed animals relative to the comparative slaughter technique. Met and Cys efficiencies were obtained separately and as total SAA values. Twenty-one 14- to 28-day-old broiler chickens were fed experimental diets containing different Met:Cys ratios (44:56, 50:50 and 56:44). Birds were given diets with daily supplements of L-(15 N) Met (60 mmol/kg) or L-(15 N2 ) Cys (35 mmol/kg) throughout the entire experimental period. Excreta were collected daily, and birds were euthanized at the end of the trial to collect feather-free bodies and feathers. Samples were analysed for 15 N and 15 N-Met content. The utilization efficiency for Met, Cys and Met + Cys for feather-free bodies was 55%, 75%, and 60%, while the efficiencies for feathers were estimated at 96%, 77% and 84% respectively.

Methionine to cystine ratio in the total sulfur amino acid requirements and sulfur amino acid metabolism using labelled amino acid approach for broilers.

BACKGROUND: Assuming that part of Methionine (Met) is converted into Cystine (Cys), but ignoring the rates with which such phenomenon occurs may lead to an excessive supply of Met in poultry diets. Such inconvenient could be easily avoided with the knowledge of the ideal Met:Cys/Total sulfur amino acids (TSAA) ratio and the rates of Met conversion into Cys. RESULTS: Met sources did not affect performance. Met:Cys/TSAA ideal ratio was determined using curvilinear-plateau regression model. Both optimum body weight gain and feed conversion ratio were estimated in 1007 g/day and 1.49, respectively, at 52% Met/TSAA ratio. Feed intake was not affected by Met:Cys/TSAA ratios. In the labelled amino acid assay, the rates with which Met was converted into Cys ranged from 27 to 43% in response to changes in Met:Cys/TSAA ratios, being higher at 56:44. CONCLUSION: Based on performance outcomes, the minimum concentration of Met relative to Cys in diets for broilers from 14 to 28 d of age based on a TSAA basis, is 52% (52:48 Met:Cys/TSAA). The outcomes from labelled amino acid assay indicate that highest the Met supply in diets, the highest is its conversion into Cys.