Isolation And Screening Of Yeast From Rumen And Its Effect On Rumen Fermentation In Vitro

As a feed additive,yeast plays an active role in improving rumen microecological environment,stabilizing rumen pH,and maintaining their health status.Ho wever,most of the yeast strains used in production were isolated from the natural environment,and this might be one of the reasons for the inconsistent reports on the effects of yeast on rumen fermentation.This study would isolate yeast from rumen fluid and determine the activity of yeast,which would lay a foundation for its application in ruminants.The contents of this experiment included:?1?yeast strains were isolated,screened and identified from rumen fluid of cows by medium conditions;?2?the effect of isolated rumen yeasts on in vitro fermentation.?1?Isolation,screening and identification of the yeast from rumenIn this study,rumen yeast with acid tolerance and oxygen consumption was isolated and screened.In the experiment,the ruminal fluid was used as the source of yeasts,and 12 suspected yeast strains were obtained by smeared plate and lineation method.Using wort culture medium of different pH,6 suspected yeast strains?yeast 1,yeast 2,yeast 3,yeast 4,yeast 5 and yeast 6,respectively?with normal growth could be preliminarily screened,and 2 suspected yeast strains?yeast 4 and yeast 5?with relatively strong acid tolerance and oxygen consumption could be screened by using wort culture medium with different O ₂ content.The molecular identification test of ITS showed that the two strains of rumen yeast obtained above were Candida strains.?2?Effect of rumen yeast on in vitro fermentation under different pH and oxygen conditionsThis study consisted of two parts.The first part adopted a 2×3 random complete block test design,one factor was the pH of the fermentation fluid?pH5.8 and pH6.5?,and the other factor was yeast?3 treatments including control group and 2 kinds of rumen yeast 4 and 5 groups?,each treatment was repeated 5 times.The fermentation substrate was Leymus chinensis and concentrate,and the amount of yeast added was 2×10⁷ CFU/m L culture solution.The second part used a single factor test design,which was divided into 6 groups,and each group was of 5 replicates.Control group?anaerobic group,+substrate?,O₂group?substrate+O₂?,2 groups of yeast group?substrate+yeast4,substrate+yeast5?,2 groups of yeast+O ₂?substrate+yeast4+O₂,substrate+yeast5+O₂?,O₂addition was 1.5 m L air?1%of the dry matter of the substrate?.The results showed that pH had a significant effect on the gas production of in vitro fermentation,and yeast 4 and 5 had different effects on the gas production at different pH values.However,during in vitro fermentation for 4-48h,the gas production of two strains increased significantly at pH5.8 and pH6.5?P<0.05?,and the gas production of in vitro fermentation of yeast4 was significantly higher than that of bacteria 5?P<0.05?.In addition,pH had significant effects on NH3-N,MCP,acetic acid,propionic acid,total VFA and lactic acid in fermentation?P<0.05?.The acetic acid,total volatile fatty acid and acetic acid/propionic acid concentrations of yeast 4and 5 at pH6.5 were significantly higher than that at pH5.8?P<0.05?,while the propionic acid concentration,NH₃-N concentration and lactic acid concentration were significantly lower than that at pH5.8?P<0.05?.The variation trend of MCP protein content and NH ₃-N concentration was the same.Compared with the control group,the concentrations of acetic acid,propionic acid and total volatile fatty acid of yeast 4 and 5 increased significantly under different pH conditions,and the concentration of acetic acid/propionic acid was increased?P<0.05?.The effect of yeast 4 was better than that of bacteria 5 except propionic acid?P<0.05?.Yeast 4 and 5 significantly increased the concentration of NH3-N and decreased the concentration of lactic acid at pH5.8?P<0.05?,however,there was no difference in the effect between the two yeasts?P>0.05?.The quantity of ruminoccous albus,ruminoccous flavefaciens,fibrobacter succinogenes and butyrivibrio fibrisolvens in the fermentation broth was significantly higher than that in pH5.8?P<0.05?.Compared with the control group,the addition of yeast 4 and 5 significantly increased the level of ruminoccous albus,ruminoccous flavefaciens,butyrivibrio fibrisolvens and megasphaera elsdenii,and significantly decreased the content of lactobacillus and streptococcus bovis?P<0.05?.After 48h of fermentation,compared with the control group,the O₂ group reduced the content of propionic acid and total volatile fatty acids,and increased the ratio of acetic acid to propionic acid.The gas production of the yeast4+O₂ group and yeast5+O₂ group was lower than that of the yeast4 group and the yeast5 group,but was higher than that of the O₂ group.Compared with the control group and the O₂ group,yeast4+O₂ and yeast5+O₂ group significantly reduced the abundance of streptococcus bovis and lactobacillus,and increased the number of megasphaera elsdenii?P<0.05?.Compared with the O₂ group,the yeast4+O₂ group and the yeast 5+O₂ group increased the content of acetic acid,acetic acid to propionic acid ratio and total volatile fatty acid,and de creased the content of lactic acid.The above results indicated that the oxygen affected the normal fermentation,and adding yeast could alleviate the harmful effect of O ₂.Combined with the above results,the effect of adding yeast 4 was better than that of adding yeast 5?P<0.05?.