26 September 1997

August humidity opened doors to lungworm larvae

By Jessica Buss

ADULT cattle are at increased risk from lungworm this autumn after the warm, wet August which has provided ideal conditions for infection.

Devon vet Andrew Biggs of The Vale Vet Group, Tiverton, has seen five dairy herds suffer husk – a disease more common in youngstock – this autumn. Cases are increasing because the wet August has activated lungworm larvae which are presenting an increased challenge to cattle with low natural immunity.

Mr Biggs believes long-acting wormers have reduced parasite levels on grass year-on-year, so there is no guarantee of young animals being infected with lungworm and building up immunity for later life. Vaccine use has also decreased.

In the past vaccination allowed calves to develop natural immunity, which was maintained by low level exposure. Now many farmers have stopped vaccinating, and because the effectiveness of modern wormers reduces the number of larvae produced, there is less exposure to infection.

"Animals are not seeing enough lungworm challenge until they join the main herd," says Mr Biggs.

Pasture grazed by the milking herd will support a low level of lungworm infection because immune cows continue to pass low numbers of lungworm.

Then when heifers join the main herd they become exposed to lungworm larvae on the cow pasture at a time when their own anthelmintic protection is lost. They become infected, throw out larvae in high numbers which in turn overcomes the immunity in adult cattle, which also succumb to infection.

"Cows will be seen to cough, milk yields will fall and cows may suffer pneumonia following infection," says Mr Biggs. Infected cattle should be wormed or vaccination may be effective when the disease is caught early on.

Independent vet consultant Tony Andrews also advises watching for cases in bought-in stock. Worm bought in-heifers at least twice before calving, and keep separate from other stock, he says.

To prevent re-occurrence of infection, ensuring heifers have natural immunity must be a priority, says Mr Biggs, who advises vaccinating stock to guarantee exposure.

Heifers not vaccinated before their first grazing season may be blood tested to check their immune status.

Those without immunity can be vaccinated before turnout next spring. But because the vaccine is fresh it must be ordered in advance through a vet, he adds.

Vet Andrew Biggs…

adult cattle are at increased risk from lungworm.