| Heat stress is a common problem for keeping laying hens in most areas of China in summer.Heat stress can lead to the decrease of laying rate,egg weight,fertilizing rate and hatchability of eggs the increase of breakage rate,and the decrease of resistance and immunity of chickens,and even large number of death,resulting in huge economic loss.Therefore,it is urgent to find a reliable way to cope with the poor growth of the laying hens and the decline of egg production rate caused by heat stress.The composition and activity of intestinal microflora are very important for the growth of poultry.Therefore,the purpose of this study is to explore the feasibility and related mechanism of reducing poor growing and laying performance of laying hens caused by heat stress with using Flammulina Velutipes stembase(FVS)as feed supplement.72 84 d ISA Brown hens were randomly divided into 6 groups: normal control group(CON),heat stress control group(HS),heat stress antibiotic group(ANT),heat stress 2% FVS group,heat stress 4% FVS group and heat stress 6% FVS group.Each group had 3 laying hens with 2 repetitions.The experiment was from 84 d to 112 d for a period of 28 d.During the test,the heat stress(temperature 38±1?,relative humidity 50%-60%)was 10 h from 8:00 to 18:00 every day,and the temperature was gradually reduced to room temperature(28±1?).The layers were slaughtered and sampled at 14 d and 28 d,respectively.The growing performance,enzyme activity,heat stress protein 70mRNA(HSP70)expression,cecum length and weight,intestinal flora diversity,short chain fatty acid(SCFAs)content and pH value of layers were detected.Result:1.During the whole heat stress,the average daily gain(ADG)of layers in 4% FVS and 6% FVS groups were significantly higher than that of the HS group(P<0.05),and there was no significant difference between the CON group and the ANT group(P>0.05).At 14 d,the average daily feed intake(ADFI)of 6% FVS group was significantly lower than that of other groups(P<0.05),and the feed conversion rate(FCR)was significantly lower than that of HS group(P<0.05),and there was no significant difference between FVS group FCR and CON group and ANT group(P>0.05).At 28 d,the ADFI of FVS groups decreased to a different degree compared to the other groups(P>0.05),the FCR of FVS groups were significantly lower than that of the HS group(P<0.05),FCR of 2% FVS group had no significant difference from the CON group(P>0.05),and there was no significant difference between 4% FVS group and ANT group(P>0.05).These results suggested that FVS could alleviate the effect of heat stress on the growing performance of laying hens,improve the growth performance of laying hens,and might have the potential to replace antibiotics.2.After 14 d of heat stress,duodenal amylase activity of FVS groups were significantly higher than that of the HS group and ANT group(P<0.05);jejunum amylase activity of 6% FVS group was significantly higher than that of the HS group and ANT group(P<0.05);ileal amylase activity of the ANT group was significantly higher than that of the HS group(P<0.05),the activities of duodenal proteinase in 4% FVS and 6% FVS groups were significantly higher than that in the HS group(P<0.05).The activities of protease in jejunum and ileum of FVS groups were significantly higher than that in the HS group(P<0.05),the activities of duodenal lipase in FVS groups were significantly lower than those in the ANT group(P<0.05),the jejunal lipase activity of 4% FVS group was significantly higher than that in the CON group(P<0.05),and the activity of lipase in FVS groups were significantly higher than that in the HS group(P<0.05).After 28 d of heat stress,the duodenal amylase activities of 2% FVS and 6% FVS groups were significantly higher than those in the HS group(P<0.05).The jejunal amylase activities of 4% FVS and 6% FVS groups were significantly higher than those in the HS group(P<0.05),and the activities of ileal amylase in FVS groups were significantly higher than those in the HS group(P<0.05),the activity of duodenal proteinase in 4% FVS group was significantly higher than that in the HS group(P<0.05),and the activities of jejunum proteinase in 4% FVS and 6% FVS groups were significantly higher than those in the HS group(P<0.05),the activities of duodenal lipase in FVS groups were significantly higher than those in the HS group(P<0.05),and the activities of jejunum lipase in 4% FVS group were significantly higher than those in the HS group and ANT group(P<0.05).This indicated that FVS could alleviate the effect of heat stress on the activities of amylase,protease and lipase in the small intestine of the laying hens,increase the enzyme activity of the small intestine,promote digestion and absorption,and have might the potential of antibiotic substitutes.3.The expression of HSP70 mRNA in FVS groups were significantly lower than that in the HS group(P<0.05).This indicated that heat stress did affect the laying hens,and FVS could alleviate the effect of heat stress on the expression of HSP70 mRNA in jejunum,and might have potential to replace antibiotics.4.The length and weight of cecum in the layers of the FVS groups were all higher than those in the heat stress group,but the difference was not significant(P>0.05),and there was no significant difference between the FVS groups,CON group and the ANT group at day 14(P>0.05).At 28 d,the weight of cecum in FVS groups were significantly lower than that in the CON group(P<0.05),and there was no significant difference between the ANT group(P>0.05).The above results suggested that FVS alleviated the effect of heat stress on the intestinal tract of laying hens,and the effect was similar to that of antibiotics.5.The number of microflora bands in FVS groups were significantly higher than that in the HS group(P<0.05),the number of microflora bands in 4% FVS group was significantly higher than that in the CON group(P<0.05),and the number of microflora bands in 2% FVS and 4% FVS group was significantly higher than that in the ANT group at 14 d after heat stress(P<0.05).At 28 d,there was no significant difference among the groups(P>0.05),but the numbers of microflora bands in group 2% FVS and 6% FVS were higher than that in other groups(P<0.05).This suggested that FVS could alleviate the effect of heat stress on the number of cecum bacteria,and enrich the cecum flora,and it might have the potential to replace antibiotics.6.During the whole experiment,among the CON group,HS group and ANT group,the highest intestinal microflora similarity is between the CON group and ANT group,followed by the HS group and ANT group,the lowest similarity is between the CON group and the HS group.The similarity between the FVS groups and ANT group was the highest.The results showed that heat stress had effect on the intestinal microflora of laying hens.FVS had a similar effect to the antibiotic group,which could alleviate the effect of heat stress on the intestinal flora.7.The number of acid producing bacteria increased in FVS groups.At 14 d,the acid producing bacteria in FVS groups were mainly Coprococcus comes,Intestinimonas butyriciproducens strain,Alistipes inops strain,Merdimonas Merdimonas,butyriciproducens and Intestinimonas.At 28 d,the acid-producing bacteria in FVS groups were mainly Oscillibacter sp.,Rikenella microfusus,Stomatobaculum longum strain and Coprobacter fastidiosus.At 14 d and 28 d,the pathogenic bacteria in the HS group were Helicobacter pullorum and Alistipes finegoldii respectively.At 14 d,Bacteroides uniformis was present in the CON group,ANT group,4% FVS group and 6% FVS groups.These results suggested that FVS could increase the number of intestinal acid producing bacteria,which is beneficial to regulating the intestinal microenvironment and alleviating the effect of heat stress on the intestinal flora.8.The SCFAs content in the HS group was significantly higher than that in other groups(P<0.05)at 14 d,the total SCFAs content in the HS group was significantly higher than that in other groups(P<0.05),and the total SCFAs content in the FVS groups were significantly higher than that in the CON group(P<0.05).At 28 d,acetic acid content in the 2% FVS and 6% FVS groups were significantly higher than that in the CON group(P<0.05),and the content of acetic acid in the 2% FVS group was significantly higher than that in other groups(P<0.05),the butyric acid content in the FVS groups were significantly higher than that in the CON group(P<0.05),and the total SCFAs content in the 2% FVS and 6% FVS groups were significantly higher than that in the CON group(P<0.05).The above results suggested that FVS could alleviate the effect of heat stress on the content of SCFAs in the cecum of laying hens.9.After 14 d of heat stress,the content of acetic acid and butyric acid in 4% FVS group was significantly higher than that in the CON group(P<0.05),and SCFAs content in FVS groups were significantly lower than that in the HS group(P<0.05).The total SCFAs content in the HS group was significantly higher than that in other groups(P<0.05),and there was no significant difference between the total SCFAs content in the 2%,6% FVS group and the CON group(P>0.05).At 28 d,the SCFAs content in 2% FVS group was significantly higher than that in the CON group(P<0.05).Compared with the HS group,the SCFAs content in the 2% FVS group increased(P>0.05),and the propionic acid content in the 2% FVS group was significantly higher than that in the HS group(P<0.05).The total SCFAs content in the ANT group was significantly higher than that in other groups(P<0.05).The total SCFAs content in the 4% and 6% FVS was significantly lower than that in the HS group(P<0.05),but there was no significant difference between with the CON group(P>0.05).The above results suggested that FVS could alleviate the effect of heat stress on the content of SCFAs in the cecum of laying hens.10.The pH value of group 2% FVS was significantly higher than that in the CON group at 14 d(P<0.05).At 28 d,the value of pH in the FVS groups were significantly lower than that of other groups(P<0.05).These results suggested that FVS could alleviate the effect of heat stress on the pH value of the cecum,and reduce the pH value of the intestinal tract with the similar effect of the antibiotic.Conclusions: Under heat stress,FVS can be used to increase the expression of jejunal mucosal HSP70 mRNA,to alleviate the effect of heat stress on chicken growing performance,and intestinal enzyme activity,to improve the growing performance of laying hens,and to promote digestion and absorption.FVS can also be used to increase the length and weight of the cecum,enrich intestinal microflora,to improve intestinal acid-producing bacteria and SCFAs content,as well as to reduce the intestinal pH value,which is conducive to regulating the intestinal microenvironment and promote intestinal health. |
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