This experiment was carried out to evaluate ability of some plant feed additives to replace synthetic vitamins, prebiotics and antibiotics in feeding layers Japanese quail layers reared under chronic heat stress. Two hundreds females and 80 males of Japanese quails were selected and distributed randomly into 10 experimental treatments with 4 replicates per each. Each replicate hold 5 female and 2 male. Ten experimental supplementations were added to basal diet (control treatment) to compose 10 experimental treatments. The other 9 treatments were formed by adding 0.5gm oxytetracycline (20%) /kg diet, 200mg vitamin C/kg diet, 20mg vitamin E/kg diet, 1gm pectin/kg diet, 20gm entire fresh lemon (fully grinded) /kg diet, 250 mg silymarin (Si) /kg, 250 mg curcumin (CR) /kg, 500 mg SI /kg and 500 mg CR /kg respectively. The experiment extended from 8 weeks of age up to 2 months of egg production. The results showed that:
Egg production performance of quail fed diet supplemented with fresh lemon equalized with vitamin E and  recorded (p ≤ 0.05) significantly higher egg production performance than vitamin C, pectin, antibiotics and other plant feed additives. On contrast laying quail fed diet supplemented with 500 SI mg CR/kg recorded numerically the highest fertility and hatchability percent. Similarly egg quality improved numerically with silymarin supplementation.
The results of this experiment recommend that some plant feed additives that are available with low cost may be able to substitute antibiotics, synthetic vitamins and prebiotics in diets to improve performance of laying quail reared under chronic heat stress.