This study was carried out to investigate the impacts of threonine(Thr) supplementation on growing Japanese quail performance. A total number of the experimental birds was 405 at 7 days of age. Japanese quails were divided into nine treatment groups (45 birds in each). Each treatment group contained three replicates ( 15 birds in each). Threonine supplementation levels to basal diet were (0.0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35 and 0.40% to form 9 experimental diet groups. The results showed that
1- Growth performance: No significant difference among dietary treatments in LBW and LBWG values during all periods (7-21, 22-42 and 7-42 days of age), FI during the period from 7-42 days of age and FC during the periods (21-42 and 7-42 days of age) were observed. Significant effects on FI during the periods (7-21 and 21-42 days of age) and FC during the period from 7-21 days of age were observed. Quails fed (basal diet +0.20% threonine supplementation (diet 5) had better FC value during the period from 7-42 days of age.
2- Slaughter parameters: Feeding different levels of threonine supplementation insignificantly affected slaughter parameters of Japanese quails, expect, breast perimenter length (cm). Quails fed basal diet + 0.40% threonine supplementation (diet 9) had higher breast perimenter length (cm).
3- Economical efficiency: Quails fed basal diet + 0.05% threonine supplementation (diet 2) gave the best economical and relative efficiency values being 2.779 and 111.56 %, respectively followed by quails fed basal diet + 0.2% threonine supplementation (diet 5) (2.776 and 111.44% respectively) when compared with control diet or other dietary treatments.
4- Chemical analysis (moisture, Cp and amino acids)% of breast Japanese quail meat: It shows no significant effect on moisture, protein and amino acids % of quails meats. However, 0.20, 0.30 and 0.40% supplemented Thr showed the highest protein % (as dry matter) were 82.55, 81.95 and 80.10 % Also, moisture % decreased as dietary threonine increased up to 0.35% Thr supplemented. Overall, as dietary threonine supplementation breast meat of Japanese quails content of Thr increase with no significant differences.
5- It can be concluded that breast perimenter length gets better as dietary threonine supplementation increase, also, supplementation of 0.05% threonine improved economic efficiency percentages and gave the net profit.