| A high-concentrate diet is usually used in ruminant production to improve economic benefits due to shortage of high-quality roughage resources in China.A large number of fermentable carbohydrates are rapidly degraded in the rumen,which will cause a series of nutritional metabolic diseases and increase the incidence of subacute rumen acidosis(SARA).SARA will lead to a decrease in rumen pH,disturbance of microbial flora,impaired immune function,release of ruminal toxic substances and then trigger a series of inflammatory reactions,which will bring huge economic losses to ruminant industry.The aim of this experiment was to investigate the effects of saccharomyces cerevisiae preparations additives on rumen fermentation,microbial flora,blood biochemical parameters,antioxidant functions,and immune function of Hu sheep under SARA condition by in vivo and in vitro experiments,and to explore the regulatory effect of saccharomyces cerevisiae preparation additives on SARA,so as to provide a basis for the application of saccharomyces cerevisiae preparation additives in ruminant production.This study included three experiments.Trial 1:Relieve effect of saccharomyces cerevisiae preparation on SARA model of Hu sheep in vitroIn this experiment,a SARA model was established by in vivo combined with in vitro culture.Three healthy adult castrated hu sheep with similar body weight and permanent rumen fistula were selected as the rumen fluid donors.In vitro batch culture was conducted to investigate the effect of two different saccharomyces cerevisiae preparation additives(ADY and YC)on rumen fermentation parameters of SARA model.Six different levels of ADY and YC(0,0.5%,1.0%,1.5%,2.0%and 2,5%)were supplemented into substrate for 24h in vitro culture.Rumen fermentation parameters were determined,and moreover,the multi-index composite index(MFAEI)was evaluated.The results showed as follows:1)The SARA model in vitro was established successfully by in vivo combined with in vitro culture.2)With ADY supplementation,the pH of rumen fermentation fluid significantly increased(P<0.05),the concentration of lactic acid significantly decreased(P<0.05),the content of NH3-N significantly increased(P<0.05),the percentage of propionic acid significantly increased(P<0.05),the content of total volatile fatty acids(TVFA)significantly increased(P<0.05),and the percentage of butyric acid was not significantly affected(P>0.05).The MFAET results showed that substrate supplemented with 1.5%ADY(dry weight basis)exhibited a better mitigative effect on SARA model of Hu sheep in vitro.3)With YC supplementation the pH of rumen fermentation fluid significantly increased(P<0.05),the concentration of lactic acid significantly decreased(P<0.05),the content of NH3-N significantly increased(P<0.05);the percentage of acetic acid significantly decreased(P<0.05),the percentage of both propionic acid and butyric acid significantly increased(P<0.05),and the content of total volatile fatty acids(TVFA)significantly increased(P<0.05).The MFAET results showed that substrate supplemented with 2.0%YC(dry weight basis)exhibited a better mitigative effect on SARA model of Hu sheep in vitroTrial 2:Effect of saccharomyces cerevisiae preparation additives on the rumen fermentation and microbial structure on SARA of Hu sheep induced by high-grain dietA 3 × 3 Latin square experiment was designed to investigate the effects of the addition of ADY and YC on rumen fermentation and rumen microbial flora in SARA state induced by high-grain diet.Six healthy adult Hu sheep with similar weight and permanent rumen cannulas were assigned to three groups with two replicates in each groups and adapted to three dietary treatments including basal diet(the control group),basal diet supplemented with ADY(the ADY group)and basal supplemented with YC(the YC group).The supplementation levels of ADY and YC referred to the result of trial 1.The experiment was divided into three phases with 21 days(14 days for adaptation and 7 days for sampling)for each phase.During the adaptation,the ratio of NFC/NDF in diet was increased gradually to 2.21 for SARA induction,then the ratio of NFC/NDF remained at 2.21 during the experimental period.The rumen fluid samples were collected at 0h,3h,6h,9h,and 12h after feeding on the last day of each experimental period.The pH,NH3-N content,lactic acid content,cellulase concentration,VFAs content of rumen fluid at each time point were measured,and the rumen fluid at 6h was used for rumen micro flora analysis.The results showed that:1)The SARA model in vivo was successfully established by gradually increasing the NFC/NDF level.In addition,the duration time of rumen fluid pH value lower than 5.8 was lasted more than 3h every day.2)With ADY supplementation,the pH of rumen fluid significantly increased at 0h and 12h(P<0.05),the duration time of rumen fluid pH lower than 5.8 was significantly shorten(P<0.05),the concentration of lactic acid and NH3-N significantly decreased(P<0.05),the cellulase concentration significantly increased(P<0.05),the percentage of acetic acid significantly decreased(P<0.05),the percentage of propionic acid significantly increased(P<0.05),the content of TVFA significantly increased(P<0.05).the rumen fermentation type was transformed from acetic acid fermentation type to propionic acid fermentation type.3)With YC supplementation the pH of rumen fluid significantly increased(P<0.05),the duration time of rumen fluid pH lower than 5.8 was significantly shorten(P<0.05),the concentration of lactic acid significantly decreased(P<0.05),the concentration of NH3-N significantly increased(P<0.05),the cellulase concentration significantly increased(P<0.05);the percentage of propionic acid significantly increased(P<0.05),the content of TVFA significantly increased(P<0.05)The rumen fermentation type was transformed from acid fermentation type to propionic acid fermentation type.4)With ADY and YC supplementation,the rumen microbial richness and diversity were not significantly affected(P<0.05),but the relative abundance of pseudomonas and actinomycota significantly decreased(P<0.05),the relative abundance of bacteroides significantly increased(P<0.05),and the relative abundance of the genus rumen and bifidobacterium significantly decreased(P<0.05).With YC supplementation the relative abundance of pseudomonas significantly increased(P<0.05).In summary,the addition of ADY and YC can relieve the symptoms of SARA and change the structure of rumen microbial floraTrial 3:Effect of saccharomyces cerevisiae preparation additives on blood biochemical indicators,immune responses and antioxidant index on SARA of Hu sheep induced by high-grain dietThe experimental design was the same as trial 2.The blood was collected through jugular vein before feeding on the last day of each experimental period.Then blood biochemical indicators,immune responses and antioxidant index were measured.The results showed that:1)With ADY and YC supplementation,the content of alanine aminotransferase in serum significantly decreased(P<0.05),the content of urea nitrogen significantly increased(P<0.05).The content of triglyceride significantly decreased with YC supplementation(P<0.05),but no significant changes of triglyceride content was observed with ADY supplementation(P>0.05).2)supplementation with YC supplementation significantly decreased the content of alanine aminotransferase in serum(P<0.05),increased the content of glutathione peroxidase and the total antioxidant capacity(P<0.05)however,supplementation with ADY had on effects on the antioxidant indexes in serum(P>0.05).3)Supplementation with YC significantly decreased the content of Toll like receptor-4,interleukin-1?,haptoglobin,serum amyloid A,lipopolysaccharide binding protein and lipopolysaccharide(P<0.05),significantly increased the content of interleukin 10 and immunoglobulin A(P<0.05),and reduced the inflammatory response caused by SARA to improve the body's immunity.Supplementation with ADY significantly decreased the content of immunoglobulin A(P<0.05),and alleviated the inflammatory response caused by SARA to improve the body's immunity. |
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