Rehearsal For Thesis Presentation

Heat stress seriously affects the growth performance and physiological functions of chickens. Early-age thermal manipulation (TM) is one of the methods to improve the heat stress tolerance of chickens. TM can slow down the impact of heat stress on the growth performance and physiological metabolism of chickens. Intestinal microbiota can maintain normal intestinal function and regulate host metabolism. Heat stress was reported to cause intestinal damage and microbita imbalance through the action of the microbiota-gut-brain axis increasing the abundance of pathogenic bacteria and reducing the abundance of beneficial bacteria. There is still lack studies on the effect of TM on the intestinal microbiota of chickens after acute heat stress. Therefore, the purpose of this study was to explore the effect of TM on the cecal microbiota of broilers and broiler type B strain Taiwan country chickens after acute heat stress. The experiment used 68 male broiler type B strain Taiwan country chickens and 100 male Ross 308 broiler. Half of the chickens received a 24-hour TM at 38°C and a relative humidity of 70% (thermal manipulation, TM) at 3 days of age, and the other half were raised at 32°C and 70% relative humidity as a control group (control, CT). All the chickens were raised in chambers with temperature gradually lowered to 25°C and 60% relative humidity until 28 days of age. At 28 days of age, half of the chickens in each group were reared at 25°C and 70% relative humidity (thermal neutral, TN) or at 36°C and 70% relative humidity for 6 hours as a acute heat stress (HS) group. Eight chickens of each group were sacrificed at 28 days and 35 days to collect intestinal samples for intestinal morphological analysis and cecal microbiota analysis. The V3 and V4 regions of cecal bacterial 16S rRNA gene were amplified and sequenced for microbiota analysis. The microbiota among groups were  compared by α, β diversity and linear discrimination analysis. The biological pathways that the microbiota may participate in were searched against the KEGG database. The results showed that the body weight and body weight gain of 7-day-old broilers in TM group were significantly lower than those of the control group. The rectal temperature of TM group B strain Taiwan country chickens was significantly higher than that of the control group from 14 to 28 days old. The rectal temperature of the chickens in the TMTN group was significantly higher than that of the control group. The rectal temperature of broilers at 7 and 21 to 28 days of age was also significantly higher than that of the control group. The rectal temperatures of chickens with TM treatment at 3 days of age in the two breeds were significantly lower than those of the control group. TM also caused a significant decrease in the villi height of the jejunum and ileum in B strain Taiwan country chickens and a significant decrease in the depth of the ileal crypts. TM caused changes in the cecal microbiota. The alpha diversity index (observe feature and chao 1) of broilers at 28 days of age decreased significantly after TM, and also decreased in the CTHS and TMHS groups at 35 days of age. The principal coordinates analysis (PCoA) showed that the bacterial flora in B strain Taiwan country chickens with HS showed distinct clusters, and the TM treatment has no significant clustering effect. Results of the LEfSe analysis showed that Eisenbergiella that produces short-chain fatty acids was significantly abundant in TMHS group than that in CTHS group of broilers. The abundance of Merdibacter, Erysipelotrichales, and Subdoligranulum that relate to the production of short-chain fatty acids was significantly higher in the TMHS group than those of the CTHS group in B strain Taiwan country chickens. The biological pathways prediction showed that the microbiota related to lipopolysaccharide synthesis, folic acid synthesis, and vitamin B6 metabolism differed significantly among groups. In summary, TM reduced the body temperature of heat-stressed broilers, and may improve the lipid metabolism of both breeds of chickens. TM also change the cecal microbiota, increase the abundance of beneficial bacteria, and may have the effect of improving the physiological functions of broiler chickens.
 
Keywords: heat stress、early thermal manipulation、intestinal microbiota、broiler、broiler type B strain country chicken

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