الفهرس 
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Abstract
The present study was carried out at Poultry Production Department, Faculty of Agriculture, Alexandria University, Egypt, throughout October to November, 2017. The study aimed to investigate the effect of using either of growth promoters (synbiotic - organic acid -essential oil) on productive performance, blood hematological and biochemical parameters, carcass characteristics, intestinal histology as well as bacterial populations of intestine and economic evaluation of growing quails. A total number of 840, 14-day old unsexed growing quail chicks, were randomly distributed into four equal treatment groups of 210 birds in three replicates, 70 birds each. All birds were reared in floor brooder (deep litter pens) measured 3 m length × 2 m width in an open sided chicks house with continuous lighting program throughout the experiment and the minimum and maximum temperatures in the house of birds after the second week of brooding up to the end of the experimental period were 27 and 25 °C according to standard quail rearing practices. Birds were offered water and experimental diets ad libitum in mash form during all experimental period, which lasted for 4 weeks. The first group was fed the control diet without supplementation of any growth promoter (control), the other three groups; birds were fed diets supplemented with either of synbiotic (Organotic dry®), organic acid (Biomold®) or essential oil (X-tract®) as different growth promoters; each of them was supplemented with the recommended level indicated by the producing company. Studied performance traits included live body weight, body weight gain, feed consumption and feed conversion ratio. At the end of the experimental period six representative quails (3 males and 3 females), total of 72 birds, were randomly selected to study blood parameters, carcass traits, histological structure of intestine and intestinal bacterial populations. Finally, economic evaluation was performed by the end of the growth experiment. The results indicated that the groups of birds fed diet supplemented with either of essential oil or the organic acid had significantly the best values of body weight, body weight gain, feed consumption and feed conversion ratio whereas, the control group recorded (P˂0.05) the worst values. Meanwhile, the group of quails treated with synbiotic had intermediate values regarding such studied parameters. All groups of studied dietary growth promoters had higher values of red blood cells (RBCs), hemoglobin (Hb) and packed cell volume (PCV) than those of the control group fed un-supplemented diet. Although no significant difference by about 11.67,17.88 and 11.16% than than the other treatment, respectively was found among the experimental groups received either of synbioyic, organic acid or essential oil; the control group had significantly the higher value in this respect. Concerning the blood biochemical constitutes, all studied growth promoters’ treatments had significantly higher globulin concentration levels than that of the control group. Higher concentration of total lipid was detected by the essential oil treated group and, the same group along with the organic acid group recorded the highest concentration of triglyceride in comparison to the control group. No significant difference (P˃0.05) were recorded among the experimental treatments regarding either glucose or cholesterol values. Concerning liver and kidney functions, the groups treated with organic acid and essential oil had the highest values (P˂0.05) of alanine amino transferase (ALT) and aspartate amino transferase (AST) enzymes, although uric acid and creatinine concentrations did not show any significant difference among the experimental groups. The results also revealed that all groups treated with different growth promoters had significantly higher live pre-slaughter weight and relative abdominal fat weight compared to the control group. Higher pre-slaughter weight, liver and small intestine relative weights were observed for female group than male.