الفهرس 
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Abstract
Heat stress (HS) is one of the most environmental stressors challenging the poultry industry globally, causing multi-million dollar loss annually. Intestinal microbiota has functions in growth performance, immune modification and metabolic regulation in broiler chickens, which is influenced by various factors such as diet, stressors and host age. A synbiotic is a product containing a mixture of prebiotics and probiotics, which has antimicrobial and immune stimulating actions, capable of positively impacting the host by improving the natural gut microbial balance and promoting animal health. The objective of this study was to evaluate the influences of dietary supplementation of a synbiotic contained fructooligosaccharides, as prebiotics, and four microbial strains (Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis, and L. reuteri), as probiotics on the behavioral patterns, performance, intestinal microbial ecology, intestinal histomorphology, some physiological parameters especially heat shock protein (HSP) 70 of broiler chickens exposed to heat stress. Three hundred and sixty male Ross 708 broiler chicks at 1 day of age were randomly distributed to three dietary treatments containing 0 (control), 0.5 (0.5X) and 1.00 (1.0X) g kg-1 synbiotic, respectively. Each treatment contained eight replicates of 15 birds. Application of heat stress at 32°C was done daily from 08:00 to 17:00 starting from day 15 to 42. Forty birds per treatment (i.e. 5 birds/replicate) were randomly taken and marked with green livestock spray for behavioral observation. Instantaneous scan direct observation method was used to record the treatment effects on behavioral patterns. Performance parameters were measured at 7, 15, 28 and 42 days. Microbial analysis, intestinal histomorphology, physiological parameters were measured at the end of the experiment. Thyroid hormones, antioxidant enzymes and transcription factors were analyzed by ELISA kits. Interleukin-6 (IL-6), Interleukin-10 (IL-10) and Tool like receptor-4 (TLR-4) mRNA in spleen and heat shock protein 70 mRNA in liver and right hypothalamus were measured by RT-PCR. HSP70 in liver and right hypothalamus was measured by western blot analysis. The results suggest that the synbiotic reduces the negative effects of HS on chicken production performance and health as indicated by the changes of behavioral patterns, body weight gain (BWG), heterophile/lymphocyte (H/L) ratio, cecal pathogenic levels, intestinal histomorphology, thyroid hormones, antioxidant status and HSP70 expression. Feeding a synbiotic diet could be a useful method for the poultry industry to improve chickens health and welfare during hot seasons, especially in the tropical and subtropical areas.
Key words: Heat stress, Broiler Chicken, Synbiotic, Welfare, Heat shock protein 70.