With the grazing season coming to a close, it is worth reviewing treatment and control of lungworm. It usually affects young stock grazing their first summer, with adult cattle only showing signs after a severe challenge.

Peak disease occurs from July through to October, with heavy infestations more common after wet summers. Infection can result in death, a reduced milk yield and up to 50% loss of body condition, and it can take up to six months more to finish cattle. In severe outbreaks, it is estimated that lungworm can cost £50 to £100/case. Cattle are infected by ingesting larvae, which live on the pasture after being expelled from infected cattle earlier that same season. Larval overwintering can occur during mild winters.

Clinical signs occur two to four weeks after ingestion, as the larvae migrate from the gut to the lungs, where they reside as adults. These adults produce larvated eggs, which are coughed up, swallowed and present in the faeces from 25 days after infection. In favourable conditions, these larvae develop into their infective stage in five days.


Lungworm symptoms depend on their location within the respiratory tract, the number of infective larvae ingested and the animal’s immune state. Early symptoms include an increased respiration rate and coughing that occurs after short periods of movement.

In severe cases, cattle stand with their heads down and necks extended, and they cough frequently. Overexertion can result in panting and death as quickly as two days after the first symptoms. In dairy cows, frequent coughing is accompanied with milk drop. Large numbers within each group can be affected and secondary bacterial pneumonia will increase the severity of the symptoms.


Vaccination of calves six and two weeks before their first grazing season confers lifelong immunity and is the preferred option for control.

Careful monitoring of young stock treated with long-acting wormers is required, as they will be naive in their second grazing season. Immunity requires re-exposure over subsequent seasons.

In animals that aren’t producing milk for human consumption, a yellow wormer is the preferred choice, while eprinomectin is used in milk cows.

Worming animals with heavy infestations can initially worsen symptoms – animals with temperatures will require an anti-inflammatory.

*Laura Weir is a veterinary surgeon at Lisnafillan farm vets in Ballymena.

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