| Subacute rumen acidosis(SARA)is one of the most common type of nutritional metabolic disease in ruminant farming,which has caused huge losses to the farming industry.Yeast has the advantages of maintaining the p H in the rumen,promoting the degradation of feed fiber,and preventing acidosis.The current yeast strains are often used as a micro-ecological preparation in ruminant animal breeding,which are mainly isolated from the natural environment.The yeasts living conditions are inconsistent with the rumen environment,hindering their functions in the rumen.In order to obtain some more favorable and applicable yeast strains to ruminants,the rumen fluid derived from 4 Holstein bulls and 4 hybrid sheep was used to isolate and screen yeasts with strong lactic acid utilization ability and fast growth rate by wort agar medium.The effect of yeast on rumen fermentation was explored under the variable ratio of concentrate and roughage in feeds by the fermentation technology in vitro.The sheep SARA models were constructed by increasing the proportion of concentrates in feeds,observing the changes of rumen fluid and blood-related parameters.The therapeutic effects were observed after the sheep SARA were administered the yeast broth.The results would provide a theoretical basis for the study of ruminant microecological preparations and its application in prevention and treatment of SARA.The results were shown as following:1.The yeasts were isolated from rumen fluid and identified by 18 S r RNA sequences.Finally,eight of yeast strains were obtained with higher ratio of utilization of lactic acid and faster growth One of them was randomly chosen for further study and validated as Candida rugosa named N09.2.The simulated rumen fermentation technology in vitro was used to determinate the effect of the yeast on the main parameters of rumen fermentation under the variable ratio of concentrate in feed(5:5,6:4and 7:3).The results showed that the ratio of gas output was decreasing,while the ratio of dry matter degradation and the concentration of microbial protein tended to increase with the increase of concentrate.The p H values of the 6:4 and 7:3 groups were significantly higher than that of 5:5 group at 9,12,28 and 36hours(P<0.05).The concentration of ammonia nitrogen had not significant difference among the groups(P>0.05).The concentrations of total volatile fatty acids,acetic acid,propionic acid and butyric acid were increased,while the acetic acid and propionic acid decreased over time.3.With the increase of the proportion of concentrate in feed,the p H of rumen fluid decreased dramatically(P<0.05).When the p H continued to be lower than 5.6 and exceeded 3 h,the sheep SARA model was successfully constructed with the concentration of histamine in blood(P<0.05),the concentration of sodium and chloride ion(P<0.05)significantly increased,respectively.The inflammation was remarkable,the concentration of calcium ion was decreased,and the electrolyte metabolism was disordered.In addition,the amount of AST,GLU,urea,TP,ALB and GLB was increased without significance(P>0.05),indicating that the sheep were dehydrated.4.After SARA sheep was administrated with yeast,the rumen p H was significantly increased(P<0.05),and the concentration of lactic acid and histamine was sharply reduced(P<0.05).The sheep’s characteristics were remarkably on the 10 day after administering yeast.For examples,the concentration of lactic acid,p CO2,sodium ion,chloride ion(P<0.05)blood was reduced,while HCO3-and calcium ion increased significantly(P<0.05).In addition,the amount of AST,GLU,urea,TP,ALB and GLB was decreased,but the difference was not significant(P>0.05),indicating that the yeast alleviated the symptoms of sheep SARA.5.There was significantly different in relative abundance of species at the phylum and genus levels for sheep SARA administrated yeast under the variable ratio of concentrate to roughage in feeds(P>0.05).The Observed species,Chao1,ACE and Shannon index tended to decrease in rumen with increasing the ratio of concentrate to roughage in feeds.After administering the yeast,the Observed species,Chao1,ACE and Shannon index increased. |
