الفهرس 
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Abstract
Probiotics become one of the most popular alternatives to antibiotic growth promoters. Increasing numbers of probiotic products are being developed and widely used in animal nutrition. The most important objectives for using probiotics in animal feed are to maintain and improve the animal performance as well as preventing and controlling enteric pathogens.
Prebiotics are typically non-digestible ingredients that pass undigested through the upper part of the gastrointestinal tract stimulating the growth or activity of beneficial microorganisms (e.g., bacteria and fungi) that colonize the large bowel by acting as substrate for them.
Probiotics and prebiotics are well known for modulation of the immune system and improvement of gut health. Probiotics stimulates production of serum and intestinal natural antibodies to many foreign antigens and improve intestinal health in broiler chickens and improves growth performance and food conversion rate. Moreover, probiotics have an effect on the main physiological functions of the gastrointestinal tract; digestion, absorption and propulsion as they adhere to the intestinal wall receptors preventing colonization of the pathogenic bacterial along the intestinal wall leading to prevent development of disease.
The current study was planned to investigate the effect of oral administration of both nucleotides prebiotic and Bacillus subtilis PB6 probiotic on growth performance (by detecting feed intake and body weight gain and food conversion rate; FCR), improvement of intestinal health, size and cell population of villi by applying intestinal Histomorphology using light and electron microscopes) as well as modulation of the immune system by detecting of serum concentrations of both Interleukin-6 and Interferon-gamma in different experimental groups of broiler chickens at 22 and 31 days of age.
Regarding the immune system modulation, serum INF-γ and IL-6 concentrations were detected as immunological parameters in different experimental groups of broiler chickens at 22 and 31 days of age. Generally, compared with control group (G4), the mean INF-γ and IL-6 concentrations increased gradually in Nucleotides treated group (G1), B. Subtilis PB6 treated group (G2) and Nucleotides and B. Subtilis PB6 treated group (G3) at both 22 and 31 days of age.
Regarding INF-γ levels, in nucleotide treated group (G1), the average INF-γ concentrations at 22 days of age elevated from 125±0.56 in control group (G4) to 170±10 pg/ml in G1. Meanwhile, at 31 days of age, the average INF-γ concentrations elevated from 290±20 to 420±50 pg/ml.
Also, in B. subtilis PB6 treated group (G2), the average INF-γ concentrations at 22 days of age elevated from 125±0.56 in G4 to 183±7 pg/ml in G2. Meanwhile, at 31 days of age, the average INF-γ concentrations elevated from 290±20 to 436±43 pg/ml.
Moreover, in nucleotides and B. Subtilis PB6 treated group (G3), the average INF-γ concentrations at 22 days of age elevated from 125±0.56 in G4 to 187±11 pg/ml in G3. Meanwhile, at 31 days of age, the average INF-γ concentrations elevated from 290±20 to 443±32 pg/ml.
Regarding IL-6 levels, results revealed that in nucleotide treated group (G1), the average IL-6 concentrations at 22 days of age elevated from 16±0.76 in control group (G4) to 25±3 pg/ml in G1. Meanwhile, at 31 days of age, the average IL-6 concentrations elevated from 21±3 to 32±2 pg/ml.
Also, in B. subtilis PB6 treated group (G2), the average IL-6 concentrations at 22 days of age elevated from 16±0.76 in G4 to 28±6 pg/ml in G2. Meanwhile, at 31 days of age, the average IL-6 concentrations elevated from 21±3 to 43±8pg/ml.
Moreover, in nucleotides and B. Subtilis PB6 treated group (G3), the average IL-6 concentrations at 22 days of age elevated from 16±0.76 in G4 to 32±4 pg/ml in G3. Meanwhile, at 31 days of age, the average IL-6 concentrations elevated from 21±3 to 47±7 pg/ml.
In the current study, the effects of nucleotides prebiotics and B. subtilis PB6 probiotics supplementation on growth performance by detecting feed intake and body weight gain and FCR. The mean total feed intake of the four groups was 708 kg per group at 35 days of age.
Results of the mean body weight gain and FCR in different experimental groups of broiler chickens showed general improvement in growth performance and FCR in treated groups compared with control group. The mean body weight and FCR increased gradually in G1, G2 and G3. In the 5th week, the mean body weights were raised from 1950 g/ bird in control group (G4) to 2112, 2200 and 2250 g/ bird in G1, G2 and G3, respectively. On the other hand, FCR was improved gradually from 1.8 in G4 to 1.67, 1.59 and 1.56 in G1, G2 and G3, respectively.
In the present study, histomorpholgical changes of the duodenal mucosa in different experimental groups of broiler chickens were determined using light and electron microscopes at 22 and 31 days of age.
The results showed that the absorptive cells of the villi of all treated group (G1, G2 and G3) demonstrated changes comparing with the control group (G4) in form of hyperplasia of the cells with increases of goblet cell population.
The lamina propria of the villus of all treated groups depicted numerous lymphoid, macrophages and plasma cells in 22 day old group and the population of the plasma cells increases in 31 day old group in number and activation.
In the current study, the average lengths of the microvilli (per micron) in different experimental groups of broiler chickens were illustrated. Generally, compared with control group (G4), the average height of the microvilli generally increased in G1, G2 and G3. At 22 days of age, the average height of the microvilli elevated from 1.42 µm in control group to 1.82, 1.88 and 1.88 µm in G1, G2 and G3, respectively. Meanwhile, at 31 days of age, the average height of the microvilli elevated from 1.42 µm in control group to 2.4, 2.4 and 2 µm in G1, G2 and G3, respectively. This increase in villi length increase surface of absorption of nutrients and enhance growth and FCR.