Effects of different levels of crude protein, with and without protease enzyme supplementation, on growth performance, carcasses characteristics, and protein digestibility in growing Japanese quails

This study was carried out to evaluate the effect of different levels of dietary crude protein and protease enzyme on growth performance, carcass characteristics, and protein digestibility in Japanese quails. Four hundred fifty day-old quails were randomly distributed into nine experimental groups in a completely randomized design with 3 × 3 factorial arrangement including 3 levels of protein (18, 20 and 22%) and 3 levels of protease enzyme supplementation (0, 200 and 400 mg/kg) with five replicates and 10 birds per replicates. In 1 to 21 days of age, the highest weight gain and feed intake were achieved in birds fed diet with 22% crude protein (P<0.05). Also, birds fed with the diet supplemented with 200 ppm protease enzyme showed higher feed intake and weight gain, in comparison to the birds fed no enzyme supplemented diet (P>0.05). But, the best feed conversion ratio was seen in birds fed a diet contained 400 ppm enzyme. In 22 to 35 days of age, different dietary treatments have no significant effect on growth performance. Carcass percentage of quails fed with diets contained 20 and 22% CP was significantly higher than those fed 18% CP diet (P<0.05). Also, enzyme supplementation had beneficial effects on the carcass, breast, and thigh relative weights (P<0.05). In the 13-15 days period, CP digestibility coefficient was significantly decreased by increasing the CP level from 18 or 20 to 22%. Also, protease enzyme supplementation at 200 ppm level had significantly a positive effect on CP digestibility (P<0.05). It could be concluded that the optimal dietary CP level for growing Japanese quails for 1- 21 and 22-35 days of the growing period is 22 and 18%, respectively. Also, dietary supplementation with protease enzyme at 200 ppm level could be beneficial at 1 to 21 days of age.