| Under the background of intensive production and breeding of modern ruminants,feeding high concentrate diet can satisfy the energy and nutrition needed for rapid growth of ruminants.The high concentrates have good palatability and low fiber content,which can increase dry matter intake and improve productivity.A large number of non-structural carbohydrates can provide energy for rumen microorganisms and improve the activity of rumen bacteria.But long-term feeding high concentrate diet will have a negative impact to health of ruminants,large grain rapidly the VFA and lactic acid fermentation cannot be absorbed in rumen wall will reduce rumen p H,serious can cause SARA,resulting in decreased activity of rumen cellulose decomposition microbes,feed intake and digestibility of dry matter drops,eventually led to the decrease production performance.Currently,studies have confirmed the effect of yeast products on rumen p H stability.Therefore,this study aims to verify whether the addition of Saccharomyces cerevisia can improve the adverse effects of long-term high concentrate feeding on rumen p H while feeding high concentrate,and to explore the mechanism of yeast products stabilizing rumen p H.The first experiment to study the in vitro batch culture of live yeast and yeast cultureIn this study,the influence of active dry yeast and yeast culture on rumen liquid fermentation was investigated through in vitro batch culture experiment.A 2×4 factor design was used for trial 1 and trial 2,with two live yeast levels(6×10~5 CFU/m L and1.2×10~6 CFU/m L)and four live yeast sources,respectively.A 3×4 factor design was used for trial 3,with three yeast culture supplemental levels(1%,2%and 4%)and four yeast culture sources,respectively.By measuring the total gas production,p H value,volatile fatty acid and lactic acid concentration of fermentation liquid after in vitro fermentation,the effects of adding different levels of live yeast products to substrate with concentrate to forage ratio on the fermentation parameters of in vitro batch culture experiment were compared.The results showed that:1.The source of ADY has no effect on gas production,p H,acetate concentration and VFA composition.With the increase of ADY level,the gas production and the ratio of acetate to propionate can be significantly reduced,and there is a tendency to reduce the concentration of lactic acid and increase the p H.2.The source of YC significantly increases the p H of the fermentation broth,the ratio of propionate,and the ratio of acetate to propionate.As the YC level increases,the concentration of lactic acid in the fermentation broth tends to decrease,significantly reducing the proportion of acetic acid.The second experiment studied the effects of active dry yeast on nutrient digestion,fermentation parameters and rumen microflora of Hu sheep.In this study,4-month-old fattening Hu sheep were fed a high concentrate diet(85:15)with live yeast products,and a 2×2 factor design was used.The factors included two active dry yeast sources(Vistacell and Procreatin7)and two supplementing levels(0.6 g/d and 1.2 g/d).The transition period was 7 d and the adaptation period was 14 d.From the adaptation period,the sheep were fed a high concentrate diet twice a day(8:00 and 18:00),and the sheep were fed a live yeast solution after morning feeding(dissolved in water bath at 37℃before feeding).The effects of different active dry yeast sources and levels on apparent nutrient digestibility,nitrogen metabolism,rumen fermentation parameters and microflora of fattening Hu sheep were studied by digestion and metabolism experiments.1.The interaction between yeast source and yeast level in the high concentrate diet of fattening Hu sheep tended to increase the digestibility of ADF(P=0.078).2.Vistacell can significantly increase the number of Selenomonas ruminantium and Ruminococcus flavefaciens in the rumen fluid of Hu sheep before and after morning feeding,and increase the abundance of Firmicutes.Increasing the amount of yeast fed has a tendency to increase the number of Prevotella brevis,Ruminococcus albus and Total bacteria.3.Vistacell supplementation group had significant influence on the abundance of Firmicutes(P=0.033).The interaction between the sources and levels of yeast supplementation tended to affect the abundance of Succiniclasticum(P=0.096).In conclusion,the rumen fermentation mode promoted by the addition of ADY with the viable number of 1.2×10~6 CFU/m L tends to propionate fermentation,which is suitable as a high concentrate dietary additive for meat ruminants.YC can increase the proportion of acetate,reduce the proportion of propionate and increase the ratio of acetate to propionate.Adding 0.6 g/d/head of Vistacell active dry yeast had the best comprehensive effect on rumen microbial growth.The comprehensive effect and positive benefit suggested that 0.6 g/d/head of Vistacell should be used in the production of mutton sheep. |
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