Four cows have been culled at a Derbyshire farm amid concerns of a potential outbreak of brucellosis.
The Department for Environment, Food and Rural Affairs said it had also imposed movement restrictions on the dairy after 23 animals failed tests.
The disease causes cattle to miscarry and in humans causes undulant fever, which can have flu-like symptoms.
Defra stressed more checks were needed before they could confirm if there was a brucellosis outbreak.
Awaiting results
The four slaughtered cows showed stronger reactions to the routine blood and milk tests than the rest of the herd, said a Defra spokesman.
Cattle develop the disease when coming into contact with an infected cow's placenta or aborted foetus.
Defra said it was too early in the tests process to identify the farm involved.
It added brucella cultures are relatively slow growing and results from the further tests may not be available for at least two weeks.
The last case of brucellosis was in 2004 in Cornwall.
Defra said undulant fever had only been contracted by humans in the past after drinking unpasteurised milk.