Effect Of Lactic Acid Utilizing Bacteria On Ruminal Digestion And Metabolism And Productive Performance Of Dairy Cows

Studies have shown that rumen acidosis may be caused by the accumulation of lactic acid.On high-concentration diet,the ruminal lactic acid accumulation is mainly due to the imbalance between lactic acid-producing bacteria and lactic acid-utilizing bacteria.In this paper,after the isolating and screeninglactic acid utilizing bacteria from rumen,the best one was identification and used in the ruminal fermentation test in vitro and dairy cow feed to investigate the effects of lactic acid utilizing bacteria on rumen fermentation and production performance of dairy cows.The results of this paper can provide a scientific evidence for the appliance of ruminal lactic acid utilizing bacteria in ruminants.A strain of lactic acid utilizing bacteria,AU21-2,with fast growth rate and higher utilization rate of lactic acid was obtained.With the morphological,Gram staining and 16 S r RNA molecularmarker identification,the strain belongs to Bacillus subtilis,and its lactic acid utilization rate was 33% at 48 h.The addition amount of AU21-2 was 1×108CFU/30 ml In vitro artificial rumen fermentation for 48 h with the concentrate to roughage ratio 65:35.The test was repeated twice.The results showed that there were no significant effect of AU21-2 on the p H,NH3-N,MCP,lactic acid concentration,degradation rate,gas production and methane production of the fermentation(P>0.05).Sixteen healthy Holstein cows were choosed and divided into treatment and control group according to the block design.Each cows was fed AU21-2 with 5x109 CFU every day.The results showed that the apparent digestibility of crude fat in the treatment group was higher than that in the control group(P<0.05),and the apparent digestibility of the other nutrients had no significant effect by AU21-2;AU21-2significantly reduced the rumen p H of dairy cows(P<0.05)The addition of AU21-2 had no significant effect on milk yield,urea nitrogen and non-fat milk solids(P>0.05),but significantly increased milk fat percentage,milk protein,total solids(P<0.05),and decreased milk Lactose content(P<0.05).The above results indicate that AU21-2 has no significant effect on rumen metabolism and milk production,but canimprove milk quality.