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Aim:To study the impact of deficiency of second line limiting amino acids (SLAA; valine, isoleucine and tryptophan) on the production performance and carcass characteristics of commercial broilers.Materials and Methods:A control (T1) corn-soy diet was formulated to contain all essential AA on standardized ileal digestible basis; While in T2-a ‘moderate SLAA deficit’ diet was formulated by replacement of soybean meal with 6% rapeseed meal and T3-a ‘high SLAA deficit’ diet was formulated by replacement of soybean meal with 6% de-oiled rice bran. Each of these treatments was allotted to six replicates of ten chicks each. During the 42 days experimental period, growth performance, carcass parameters and intake of metabolizable energy (ME), crude protein (CP) and AA were studied.Results:The cumulative body weight gain, feed conversion ratio, carcass cut weights and yields of carcass, breast and thighs were decreased (p<0.05) in T3 compared to T1. The absolute intake of ME, lysine, methionine + cysteine and threonine were not affected while intake of CP and all SLAA were reduced in SLAA deficit diets. The relative intake of ME, lysine, methionine + cysteine, threonine and SLAA reduced in T3 in comparison to T1. The relative weights of internal organs were not affected by treatments while the abdominal fat percentage was increased linearly to the magnitude of SLAA deficiency.Conclusion:The deficiency of SLAA decreased performance, carcass yields and impaired utilization of ME, CP and AA linearly to the magnitude of the deficiency.

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.

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