This study was carried out to investigate the influence of dietary levels threonine on the productive and reproductive performance of laying Japanese quails. One hundred and sixty- two of adult Japanese quails (6 weeks of age) were divided into 9 treatments (18 in each). Each treatment group was divided into six replicates of 3 birds (one male and two females) in each treatment. Birds were fed nine experimental diets, where threonine supplementation levels were 0.0, 0.5, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35 and 0.40%.
Results obtained showed that: Increasing dietary threonine level caused increase in most egg productive traits of laying Japanese quail. The supplemented threonine at level 0.15 % to the basal diet significantly (P£ 0.01) showed the best results in egg weight (EW), feed intake (FI), daily egg production (DEP), feed conversion (FC), egg mass (EM), egg production (EP) and egg number (EN) of Japanese quails. However, there were significant differences (P£ 0.05) among treatment in egg weight, shape index, yolk weight percentage and Haugh units, while other measurements of egg quality did not influence by dietary threonine levels. Also, no significant differences shown among treatment groups in both males or females in reproductive organs. Dietary threonine levels at 0.20% recorded the best value of hatchability per total and fertile eggs (77.82 and 80.63%, respectively). High economic efficiency and relative economic efficiency obtained for Japanese quails fed diets supplemented with threonine (Thr) at levels 0.05 and 0.15%, respectively.
Conclusively, it could be concluded that diets of laying Japanese quails determined according to NRC recommendation were not sufficient for threonine needs. It is worthy to note that diets supplemented with Thr at levels 0.05 up to 0.15% resulted improvement in egg production traits, egg quality, hatchability (%), as well as, economic efficiency and relative economic efficiency, under Egyptian environmental conditions.