Abstract: The assay was aimed to clarify the reasons why dairy cattle became ill with the symptoms including fever,breathing difficulty,salivation and subcutaneous emphysema at neck or chest in a dairy cow farm at Hubei province,even part of dairy cows were dead for exhaustion.The disease was diagnosed by laboratory methods,and treatment scheme was proposed.The samples from heart,liver,lung or trachea tissues were collected,then M.bovis and pathogenic bacteria were isolated,respectively.Biochemical characteristics,pathogenicity test and drug sensitivity analysis were performed on the isolated pathogenic bacteria.RNA was extracted from bovine serum,then bovine ephemeral fever virus was identified by RT-PCR.The results showed that nothing grew in PPLO medium,and the isolated bacteria could form indole,but did not ferment glycogen and inositol in the biochemical tests.The isolated pathogenic bacteria was conformed as serotype A P.multocida by PCR while bovine ephemeral fever virus of RT-PCR result was negative.The pathogen could kill mice and the pathogenic bacteria could be isolated from heart blood of the dead mice in pathogenicity test.The isolated bacteria was sensitive to cefoperazone or levofloxacin in drug sensitivity analysis.In conclusion,the disease was diagnosed as bovine serotype A P.multocida infection.Some treatments including choosing sensitive antibiotic drugs based on the drug sensitivity tests,holding sick cattle under quarantine treatment and isolating suspected cattle should be taken.Moreover,some complex measures such as keeping the air flowing,cleaning up in time,improving the management,and preventing stress from congestion,cold and long distance transport were very important to prevent and control serotype A P.multocida infection in dairy cows.

Key words: dairy cow; serotype A P.multocida; M.bovis; bovine ephemeral fever; case report