JAB DOES FOR LUNGWORM
By Sue Rider
LUNGWORM was diagnosed in more cattle than average last autumn and early winter by the veterinary sciences division of the Department of Agriculture for Northern Ireland (DANI). The disease was found on 20 farms. All affected cattle were finishing either their first or second seasons at grass and died.
Furthermore outbreaks investigated by the veterinary investigation services in Scotland, England and Wales have increased from 50 in 1990 to 200 in 1994.
Shrewsbury VI centre vet Graham David confirms that lungworm cases in adult cattle have increased due to a fall in vaccinations to a quarter of the levels seen 10 years ago. At the same time use of new wormers including long-acting wormer boluses has increased.
Grazing season control
Effective lungworm and gutworm control can be achieved during most of the grazing season by boluses or a systematic programme of worming using ivermectin-based wormers.
Cattle should be treated with wormers effective against both immature and mature lungworms advises DANI vet Jo Cassidy. But timing of treatments and provision of clean pasture are important to secure effective control.
Both the bolus and dosing methods of control require all calves to be treated, warns Scottish Agricultural College vet Brian Hosie. They should also be set-stocked. No untreated cattle should be added to the pasture. When treated calves must leave pasture on which they were set-stocked, they should go only onto clean aftermath. When cattle are exposed to pasture grazed by cattle not on the system early in the year, the worming programme should be reassessed with a vet.
The wormer approach to lungworm control may fail if stock are challenged outside the period covered by wormer protection.
For example, last years dry summer and autumn encouraged a long grazing season and increased the time when cattle could pick up lungworm infection from pasture. Many of the wormer control programmes normally used to prevent lungworm failed to offer protection during this late grazing stage, explains DANI.
It also suggests that during the dry summer infective lungworm larvae survived in the soil but were not picked up by grazing cattle. In wet autumn conditions these larvae will have emerged onto pasture to provide a source of infection for cattle much later in the season than is usual.
The relatively high levels of lungworm infection in cattle during the autumn and early winter of 1995 are likely to result in higher than usual numbers of lungworm larvae surviving through the winter on grass and within the lungs of cattle. It is likely then that the risk of lungworm disease in cattle will be increased in 1996, warns DANI.
Lungworm control may also fail when there has been insufficient lungworm challenge during the period covered by the wormers protection. As a result the calves natural immunity will not be stimulated sufficiently.
Immunity is necessary to provide protection against lungworm in future grazing seasons. It is thought insufficient lungworm challenge in first and second grazing seasons could explain the increase in adult cattle outbreaks.
Vaccination is the only way to ensure calves develop natural immunity. Two brands of lungworm vaccine are available. Both contain irradiated lungworm larvae. The vaccine is given to calves over two months old before their first season at grass, says DANI. Two doses are required, separated by an interval of four weeks, it advises. The calves should then be kept off pasture for a further two weeks to allow a protective level of immunity to develop.
Wormers used to control lungworm may fail when stock are challenged outside the period covered by wormer protection. Last years dry autumn encouraged a long grazing season when cattle could pick up infection.