Effects Of Heat Stress On Physiological,Biochemical And Behaviour,Gut Microbiota And Metabolites Of Xianan Cattle And Mitigation Effects Of Shade Nets

The purpose of this experiment was to study the effects of heat stress on the physiological,biochemical and behavioral welfare of Xianan cattle and the effect of shade net on heat stress,as well as to study the effect of heat stress on the fecal flora,diversity,structure and metabolites of Xianan cattle based on 16 s r DNA and metabolomics techniques.Providing ideas and technical support for improving the production performance of Xianan cattle under summer heat stress.Experiment 1 Effects of heat stress and shade net on physiological and biochemical indexes and behavior of Xianan cattleThe experiment adopted a two-factor experimental design,and selected 16 Xianan cattle with similar body weight（289.63 ± 27.32 kg）and good health status.The experiments were carried out in summer and autumn respectively,and each season was divided into shade treatment and no shade treatment（n=8）,named as summer shade group,summer open-air group,autumn shade group and autumn open-air group.The results show:（1）The average THI of the summer open-air group was 76.87,and the temperature-humidity index（THI）was reduced to 75.10 by erecting a shading net.The average THI of the autumn open-air group was 61.63,and that of the autumn shading net group was 61.10.（2）The respiratory rate of Xianan cattle in summer open-air group and summer shade net group was significantly higher than that in autumn open-air group and autumn shade net group（P < 0.001）,the respiratory rate of Xianan cattle in summer open-air group was significantly higher than that in summer shade net group（P < 0.05）,there was no significant difference in respiratory rate between the autumn open-air group and the autumn shade net group（P < 0.05）,the rectal temperature of Xianan cattle in summer open-air group was significantly higher than that in summer shade net group,autumn open-air group and autumn shade net group（P < 0.001）,The rectal temperature of Xianan cattle in the summer shade net group was slightly higher than that in the autumn open-air group and the autumn shade net group（P > 0.05）,the interaction of season and shading treatment had significant effects on respiratory rate and rectal temperature of Xianan cattle（P < 0.05）;（3）Compared with the summer open-air group,the levels of heat shock protein 70（HSP70）,heat shock protein 90（HSP90）and cortisol（COR）in the serum of Xianan cattle in the autumn two groups were significantly decreased（P <0.05）,the contents of superoxide dismutase（SOD）,total antioxidant capacity（T-AOC）,triiodothyronine（T3）and thyroxine（T4）were significantly increased（P < 0.05）;Compared with the summer open-air group,the plasma SOD and T4 of Xianan cattle in the summer shade net group showed a significant upward trend（P < 0.05）,and the COR showed a significant downward trend（P < 0.05）.（4）The drinking frequency of Xianan cattle in summer open-air group and summer shade net group was significantly higher than that in autumn open-air group and autumn shade net group（P < 0.05）,the drinking frequency of Xianan cattle in the summer shade net group was significantly lower than that in the summer open-air group（P < 0.05）,there was no significant difference in the number of drinking water between the autumn open-air group and the autumn shade net group（P > 0.05）;（5）The standing and walking time of Xianan cattle in the summer open-air group and the summer shade net group was significantly higher than that in the autumn open-air group and the autumn shade net group（P < 0.05）,the standing and walking time of Xianan cattle in the summer open-air group was slightly higher than that in the shade net group（P > 0.05）;（6）The feeding time of Xianan cattle in summer open-air group and summer shade net group was significantly lower than that in autumn open-air group and autumn shade net group（P < 0.001）,there was no significant difference in the feeding time of Xianan cattle between the summer open-air group and the summer shade net group（P > 0.05）;（7）The lying time of Xianan cattle in summer open-air group was significantly lower than that in summer shade net group,autumn openair group and autumn shade net group（P < 0.001）,the lying time of Xianan cattle in the summer shade net group was lower than that in the autumn two groups,but the difference was not significant（P > 0.05）.（8）Through the correlation analysis of each index,it was found that the respiratory rate,rectal temperature and the expression level of heat shock protein were negatively correlated with antioxidant indexes,and there was a certain correlation with behavioral indicators related to feed intake and activity.To sum up,heat stress led to the increase of respiratory frequency and rectal temperature of Xianan cattle,abnormal secretion of heat shock proteins and COR,and decreased antioxidant capacity.Experiment 2 Effects of heat stress on the gut microflora and its diversity and metabolites of Xianan cattleThe experiment selected 14 Xianan cattle with similar body weight（289.63±27.32kg）and good health status,and divided them into summer heat stress group（HS,n=7）and autumn non-heat stress group（NHS,n=7）according to the test time.The results show:（1）Heat stress significantly changed the beta diversity and alpha diversity of the gut flora of Xianan cattle（Shannon,Ace,Sobs,Simpson,Chao1,and Good Coverage）,but the difference was not significant（P > 0.05）.（2）Heat stress significantly changed the relative abundances of Proteobacteria,Planctomycetes and Lentisphaerae at the phylum level（P < 0.05）;At the genus level,the abundance of Ruminococcaceae_UCG-013,Flavonifractor,p-1088-a5_gut_group was significantly decreased（P < 0.05）,the abundances of Alistipes,Clostridium_sensu_stricto₁,Romboutsia,Dorea,Anaerovibrio,and Blautia were significantly increased（P < 0.05）.（3）Compared with the HS group,the metabolic profile of NHS Xianan cattle feces changed significantly.96 and 83 differential metabolites were screened out in the positive ion mode and the negative ion mode in the HS group and the NHS group,respectively.These differential metabolites were subjected to enrichment analysis,and the results showed that the functional differences between the HS group and the NHS group were mainly concentrated in pyrimidine metabolism,unsaturated fatty acid biosynthesis,amino sugar and nucleotide sugar metabolism,fatty acid biosynthesis,and propionate metabolism.In summary,heat stress leads to a decrease in the abundance of some probiotics and an increase of harmful bacteria,and their functions are mainly reflected in nutrient absorption metabolism and inflammation.At the same time,heat stress changes the metabolism of intestinal flora,thereby affecting the The pathways where the metabolites are located have an impact on the nutritional metabolism of Xianan cattle.