Supplementation of L-Threonine for Optimization of Dietary Crude Protein Levels in Broilers.

This study was conducted to evaluate the performance of broiler chickens fed low protein diets supplemented with L-threonine. Four hundred and sixty two 1-day-old broiler chicks were randomly allotted to seven treatments with six replicates each and eleven chicks per replicate. Seven treatments included; T1-control, T2, T4, T6-without L-threonine and T3, T5 ,T7-with L-threonine supplementation with a CP reduction by 0.75, 1.50 and 2.25 per cent units, respectively. Feed was offered in pre-starter (0-14 days), starter (15-28 days) and finisher phases (29-42 days). On cumulative basis, body weight gain (BWG) was significantly (p<0.05) reduced by step-down of dietary CP levels without L-threonine supplementation and L-threonine supplementation significantly (p<0.05) improved BWG, but not the CP reduction by 2.25 per cent unit. Feed intake was significantly (p<0.05) reduced due to CP reduction at and above 1.5 per cent unit. Meanwhile, supplementation of L-threonine improved feed intake on par to control. The FCR with L-threonine supplementation improved only at 0.75 per cent CP reduction (T3) but not with further CP reduction. The breast, thigh and drumstick absolute and relative weights were significantly (p<0.05) decreased with CP reduction, at and beyond 1.50 per cent unit. L-Threonine addition improved the breast, thigh and drumstick weights at CP reduction of 1.50 per cent units but not at CP reduction at 2.25 per cent units. Abdominal fat (AF) weight increased at and beyond 1.5 per cent units CP reduction without L-threonine supplementation and with threonine, 1.5 per cent units CP reduced diet was similar to control. The relative AF weight was increased with the CP reduction of 0.75 per cent without L-threonine supplementation, while upon addition of L-threonine, AF per cent decreased as that of control. These results conclude that, with L-threonine supplementation, the CP can be reduced by 1.5 per cent units without affecting bird performance.