Maintenance requirements for methionine and cysteine, and threonine for poultry

________________________________________________________________________________ Abstract This study aimed to estimate the methionine & cystine (M&C), and threonine (THR) requirements for maintenance of adult roosters differing in liveweight and body composition, and to estimate the concentrations of M&C and threonine in ‘ideal’ protein for maintenance. Five metabolism trials were conducted using 42 mature Bovans White (in trials 1 and 3) and 42 Cobb (in trials 2 and 4) roosters. In the first two trials, designed to measure the M&C requirements for maintenance, the M&C content in the diets ranged from 0 to 138 mg/kg d (687 mg/BPm/d) for the Bovans White, and from 0 to 64 mg/kg d (346 mg/BPm/d) for the Cobb strain, respectively (where BPm is mature body protein weight). In trials 3 and 4 in which the THR requirement for maintenance was measured, the THR levels ranged from 0 to 127 mg/kg d (624 mg/BPm.u/d) and from 0 to 106 mg/kg d (584 mg/BPm.u/d) for the two strains, respectively. Excreta were collected in trays, weighed, homogenized, dried and ground and the nitrogen contents of excreta and diets were then determined. The M&C requirement for maintenance was estimated as 19 mg/kg empty body weight (EBW)/d, 26 mg/kg EBW/d or 87 mg/BPm/d. The maintenance requirement for THR was estimated as 17 mg/kg EBW/d, 22 mg/kg EBW/d or 76 mg/BPm/d. The concentration of M&C in ‘ideal’ protein for maintenance was estimated as 11, and THR, 9.4 g/kg body protein.