Screening Of Probiotic Yeast And Its Effects On Digestibility,growth Performance And Carcass Traits Of Beef Cattle

Probiotics have been shown to improve the microbial flora balance in the digestive tract of animals,enhance animal feed efficiency,production performance and health,as well as provide no antibiotic drug residues.However,due to the confinement of the high level of proteolytic environment in the rumen,most studies on the effects of probiotics on ruminants are limited to rumen fermentation,and direct study on the effects of probiotics in the small intestine has been problematic;thus,the effects of probiotics in the small intestine in ruminants have been unclear.Four experiments were designed to screen the probiotics?lactic acid bacteria and yeast products?,study the technology of protected probiotics in the rumen and its effects on digestion and immune function of beef cattle,aiming to search for alternatives of antibiotics and provide new methods of protecting probiotics in the rumen.Main findings of individual experiment are listed below:1.Screening of lactic acid bacteria?LAB?and yeast products?YP?on ruminal fermentation in vitroThe objectives of the two studies were to screen the better candidate for the subsequent animal trials,from five lactic acid bacteria?LAB1-5,Experiment 1?and five yeast products?YP1-5,Experiment 2?,respectively,on gas production?GP?,dry matter?DM?disappearance?DMD?,volatile fatty acid?VFA?and NH_3-N concentrations in batch culture.The study included two media pH?5.8 and 6.5?and one substrate?10%barley silage,87%high-barley diet and 3%vitamins and minerals,DM basis?using monensin?MON?as positive control.The results of the first study showed that the GP and DMD at pH6.5 were higher than which at pH5.8?P<0.01?.Compared with CON,LAB tended to reduce DMD at pH5.8?P=0.06?but had no effect on DMD at pH6.5?P>0.05?.There were interactions between pH and LAB on DMD,GP,VFA profiles and NH_3-N concentration?P<0.05?.Consistent with the results of GP and DMD,total volatile fatty acid?TVFA?and the ratio of acetate to propionate?A:P?was greater at pH6.5 than which at pH5.8?P<0.01?.Also,LAB3 had higher ratio of A:P than which of other LAB treatments?P<0.05?.LAB increased TVFA at either pH5.8 or pH6.5 compared with CON?P<0.05?;however,compared with MON,LAB only improved TVFA at pH 6.5?P<0.05?.In the second study,DMD,GP and TVFA of all treatments under pH6.5 were greater than which at pH5.8?P<0.01?.YP2 had higher DMD and TVFA compared with other treatments at either pH6.5 or pH5.8?P<0.05?.At pH5.8,YP2 had higher ratio of A:P?P<0.05?.Compared with CON,YP had no effect on DMD?P?0.05?,but increased TVFA at pH5.8?P<0.01?.There were interactions between pH and YP on DMD,GP,TVFA and NH_3-N concentrations?P<0.01?.Compared with MON,despite that YP had lower DMD at pH5.8 and pH6.5?P<0.01?,YP had greater TVFA?P<0.01?and increased ratio of A:P as well as NH_3-N concentrations at both pH5.8 and pH6.5?P<0.05?.2.Effects of active dry yeast and post-ruminal protected yeast on digestion and immune function in beef cattleThe objectives of this study were to determine the effects of active dry yeast and post-ruminal protected yeast on digestion and immune function by measuring feed intake,ruminal pH and fermentation,site and extent of feed digestion,blood biochemistry and immunity parameters in beef cattle.Five Angus beef heifers with ruminal cannulas were used in a 5×5 Latin square design.High grain diet was consisted of barley grain?67%?,corn DDGS?20%?and barley silage?10%?.Five treatments were 1)control?CON?;2)antibiotics?MON?;3)active dry yeast?ADY?;4)encapsulated yeast?EDY?and 5)mixture of ADY and EDY?MDY?.The results showed that there was no difference in intakes?kg/d?of DM,organic matter?OM?,NDF,starch and N among treatments?P>0.05?.Although no difference was observed in omasal OM flow and starch flow among treatments?P>0.05?,NDF flow was affected,with MON being the highest and EDY being the lowest group?P<0.05?.Compared with CON and MON,EDY and MDY tended to decrease ruminal OM digestibility?P=0.09?,but there was no difference between treatments in NDF and starch digestibility in the rumen?P>0.05?.In addition,EDY and MDY increased OM and NDF digestibility in the intestine compared with CON and MON?P<0.05?.In comparison with CON and MON,EDY and MDY improved OM and NDF digestibility in total tract?P<0.01?.Different treatments had no impact on omasal N flow and microbial N?P>0.05?.Although treatments had no difference in ruminal and intestinal N digestibility,EDY and MDY increased N total tract digestibility compared with CON and MON?P<0.05?.Moreover,different treatments had no difference in ruminal pH?P>0.05?,VFA and NH_3-N concentrations.Treatment ADY and MDY tended to increase the population of Ruminococcus flavefaciens in the rumen compared with MON?P=0.10?.Compared with CON and MON,ADY and MDY increased protozoa counts in the rumen?P<0.01?.Compared with CON and MON,EDY had lower LBP concentration?P<0.05?.In cytokine concentrations,there was no difference on IL-1 and IL-10 concentration between treatments?P>0.05?,but MDY had lower IL-6 concentration compared with CON?P<0.05?.3.Effects of active dry yeast and post-ruminal protected yeast on growth performance and carcass traits in beef cattleThis study used 75 Angus beef cattle?BW 446±31.2 kg?as experimental animals,and high grain diet was consisted of barley grain?87%?and barley silage?10%?.Experimental animals were assigned into five groups as five treatments,including:1)control?CON?;2)monensin?MON?;3)active dry yeast?ADY?;4)encapsulated yeast?EDY?and 5)mixture of ADY and EDY?MDY?.The objectives of the study were to evaluate the effects of active dry yeast and encapsulated yeast on growth performance and carcass quality by measuring intake,average daily gain?ADG?,feed conversion rate?FCR?,and carcass traits.The results showed that compared with CON and MON,there was no difference?P>0.05?on initial body weight?BW?,final BW,DM intake,ADG and FCR between ADY,EDY and MDY,but EDY tended to decrease NEg and NEm?P=0.07?.In terms of carcass quality traits,compared with CON and MON,ADY,EDY and MDY had no difference between hot carcass weight,dressing percentage,12^th-rib fat thickness,rib eye muscle area,marbling score,saleable meat yield and liver abscess score?P>0.05?;however,compared with MON,treatments of ADY,EDY and MDY tended to have greater quality grade?P=0.08?.In comparison with CON and MON,treatments of ADY,EDY and MDY had no effects on fecal DM,pH and E.coli of beef cattle?P>0.05?,however,supplementation of MON significantly increased the fecal concentration of IgA?P<0.05??4.Effects of active dry yeast and post-ruminal protected yeast on fecal microbial flora of beef cattleThis study was conduced using 75 Angus beef cattle as experimental animals,and high grain diet was consisted of barley grain?87%?and barley silage?10%?.Five treatments included 1)control?CON?;2)monensin?MON?;3)active dry yeast?ADY?;4)encapsulated yeast?EDY?and 5)mixture of ADY and EDY?MDY?.On day 56,ten beef Angus were randomly selected from each treatment to take fecal samples.The experiment was aiming to study the microbial diversity by using 16S rRNA MiSeq sequencing technology based on the50 fecal samples from the 50 cattle.Results showed that compared with CON,treatments ADY,EDY and MDY had no difference on phylum level of individual bacterial community?P>0.05?,but MON had greater Cyanobacteria population compared with other treatments?P<0.01?.Also,MON tended to increase Proteobacteria and Verrucomicrobia population?P=0.09 and P=0.10,respectively?,and MON tended to reduce Firmicutes population compared with other treatments?P=0.09?.Compared with MON,EDY and MDY decreased Cyanobacteria population?P<0.01?,and ADY as well as EDY tended to reduce Proteobacteria and Verrucomicrobia population?P=0.09 and P=0.10,respectively?.On level of genus,compared with CON,MON,ADY,EDY and MDY all reduced Oscillospira population?P?0.05?,and MON and EDY decreased Dorea population?P<0.05?,Parabacteroides population was increased in MON and MDY treatments?P<0.01?.Compared with MON,MDY had greater Dorea population?P<0.05?,Parabacteroides population was lower in EDY group compared with both MON and MDY?P<0.01?.In conclusion,although active dry yeast and post-ruminal protected yeast had limited impact on ruminal fermentation,growth performance,carcass characteristics and fecal microbial diversity,yeast products improved OM and NDF digestibility in intestinal and total tract.Moreover,post-ruminal protected yeast showed potential of improving immune function in beef cattle.The current research not only explored the effects of yeast products in intestine of beef cattle,but also provides additional evidence on the application of yeast products in ruminants,and offers more options on the less use of antibiotics in ruminants.