28 November 1997

Dairy mastitis is threat

DAIRY producers attempting to cut costs by cutting back on antibiotic dry cow therapy, will increase the risk of sub-clinical mastitis and high cell counts after calving that will be difficult to cure.

So warns Hampshire-based dairy vet Jonathan Harwood. It is the cows you think of as clear that may well have infection, he adds.

In a trial that compared full treatment with dry cow tubes and partial treatment of cows – in which mastitis pathogens were detected at drying off – double the quarters of the partially treated group were infected with mastitis bugs at calving. Animals that were clear at drying off had bugs at calving time that would cause infection in the next three months of lactation.

"When bugs are found at calving it is too late as milk will need to be withheld and the cure rate is low at 40% compared with 60% for the dry period.

"The dry period provides a good opportunity to treat cows with a long-acting antibiotic to clear up any existing infection, and prevent new infection after drying off when still prone to infection. That infection can lie dormant until after calving," says Mr Harwood.

"Herds which have a low cell count, are in that position because of dry cow therapy; if they let it slip cell counts will get worse." And once a cow is infected with a high cell count it is difficult to cure, can be costly when bulk cell counts are increased, and some cows may need to be culled, he adds.