Extra supplementation of amino acids is considered to be good for better immune response in broilers. The aim of present study was to investigate the effect of extra supplementation of methionine (Met) and threonine (Thr) on growth performance, carcass characteristics and immune response in broilers. Three hundred day-old boiler chicks (mixed sex) were distributed into five experimental groups with six replicates (10 chicks/ replicate) in each group. Five (A, B, C, D and E) iso-caloric (ME 2850 kcal/kg) starter and five (A, B, C, D and E) iso-caloric (ME 2950 kcal/kg) finisher diets were formulated. Diet A was standard commercial diet with 100% NRC amino acids recommendations whereas diets B, C, D and E contained 110% methionine + cysteine (M+C) level, 120% M+C level, 110% threonine (Thr) and 120% Thr, respectively. Results showed that the feed inatke, weight gain and feed conversion ratio were found non-significant (P<0.05) between the treatment groups. Breast meat yield was improved (P<0.05) in chicken fed diets (B, C, D and E) with extra supplementation of Met and Thr. Highest (P<0.001) haemaglutination inhibition titer level against Newcastle disease was found in chicks (6.50) fed diet E after first vaccination and in chicks fed diet B (5.50) after second vaccination. Similarly, higher weight (5.00g) of bursa of fabricius was also found in chicks fed diet B. The ELISA titer level against infectious bursal disease was not affected (P>0.05) by dietary treatments. It is concluded that supplementation of Met and Thr above the recommended levels improve breast meat yield and immune response in chicks. However, it is not economical to do extra supplementation of Met and Thr in broiler diet in terms of growth performance.

Amino acids (AA) are protein's hydrolytic products. In the recent years, poultry diets are being formulated on digestible AA (DAA) basis rather than total AA. Different techniques including precision-fed rooster assay, precision-fed cecectomized rooster assay, ileal AA digestibility and precision-fed broiler chick assay are used to determine the DAA coefficients of feed ingredients. However, nutritionists consider that the ileal digestibility in growing and adult birds is more accurate than other techniques. In all these digestibility techniques, apparent AA digestibility is corrected for endogenous AA losses to achieve standardized AA digestibility values. The digestibility values, determined using different digestibility techniques, of any feed ingredient vary. This variation in digestibility values can be minimized by adopting same digestibility technique for the estimation of DAA coefficients. Birds fed diets formulated on DAA basis resulted in better growth performance, feed efficiency and production economics. The main objective of this review is to examine the poultry's performance fed diet formulated based on the DAA.

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Present study was conducted with the aim of replacing dietary crude protein (CP) in poultry diet with synthetic essential amino acids and to determine its effect on growth performance, slaughter data and nutrient digestibility in broilers. Five (A, B, C, D and E) iso-caloric & iso-nitrogenous (ME 2850/2950 Kcal/kg; CP 20%/18%) starter and finisher diets were formulated respectively. In both phase diet A was standard diet, in remaining starter/finisher diets (B, C, D and E) CP level was reduced (19/17, 18/16, 17/15 and 16/14) and make them iso-nitrogenous by supplementation of synthetic amino acids. Result showed no significant (P>0.05) effect of replacing CP with synthetic amino acids on all parameters of growth performance of broilers except on feed intake during starter phase. Best FCR during starter (1.33) and finisher (1.67) phase was found in broilers fed on diet B. Similarly, highest (P>0.05) dressing percentage with lowest (P>0.05) abdominal fat was observed in birds fed on diet B while highest (P>0.05) breast meat yield was found in control group. No significant (P>0.05) effect of replacing CP with amino acids was found on nutrient digestibility in both phase, highest digestibility was found in group C (75.50%) and E (79.84%) during starter and finisher phase, respectively. It is concluded that CP of boiler diet can be replaced by synthetic amino acids up to 17 and 15% in start and finisher diet, respectively without compromising the growth performance of broilers.