Abstract
OBJECTIVE: The present study attempted to determine safe and sufficient growth promoters in poultry feeding. METHODS: A total of 520 seven-day-old quail chicks were randomly allotted to eight treatment groups in a 4×2 factorial design experiment to evaluate the effect of different levels of humic acid (HA) and black cumin (BC) seed and their interactions on growth, carcass traits, gut microbes, and blood chemistry of growing quails. Quails were randomly distributed into 8 groups in a 4×2 factorial design, included 4 HA levels (0, 0.75, 1.5, and 2.25 g/kg diet) and 2 BC levels (0 or 5 g/ kg diet). RESULTS: Increasing HA level associated with a gradual increase in final weight, feed intake and body weight gain along with an improvement in feed conversion ratio. Dietary addition of 5 g BC powder/kg diet gave similar results. The highest level of HA (2.25 g/kg diet) recorded the best values of carcass weight, breast yield, intestinal length, and intestinal weight comparing with the control and other HA levels. Total viable microbial counts decreased (p<0.05) with increasing levels of HA except the intermediate level (1.5 g/kg diet). The concentration of serum cholesterol and low density lipoprotein (excluding that 0.75 g HA) decreased (p<0.05) and high density lipoprotein increased (p = 0.034) along with increasing HA level. The interaction between the 2.25 g HA×5 g gave the best results regarding most studied parameters. CONCLUSION: These findings indicated that HA combined with BC could be used as effective growth promoters, with the recommended level being 2.25 g HA+5 g BC/kg of quail diet.