Vet's column: Coughing cattle could be sign of lungworm

Lungworm, or Dictycaulus viviparous, is a roundworm that resides in the lungs of cattle.

What is the lifecycle?

The lifecycle of lungworm begins with ingested larvae on the pasture migrating from the stomach into the lungs where they develop into adults. These adults lay eggs which become larvae, they are coughed up and then swallowed. They then pass through the animal and are excreted back onto pasture.

As a result, we can diagnose lungworm by finding larvae on faecal samples. The time between ingestion of adults and excretion of larvae can be up to four weeks.

What are the clinical signs?

Lungworm may be seen at any time of year, but most commonly causes problems in late summer/autumn time after turnout through summer. Young immune naive animals are most at risk. The most obvious clinical sign is respiratory distress – coughing and breathlessness on a group level, especially after exercise. More subtle signs include weight loss and milk drop in dairy herds. The classic sign is animals standing with their neck stretched out, open-mouthed breathing.

Sudden death may be the first sign of a problem, especially if immune naïve animals are suddenly exposed to large numbers of larvae. In these cases, adult worms will be found in the upper airways on post-mortem. Chronic lungworm infection may lead to secondary bacterial pneumonia.

How can it be controlled?

Resistance to lungworm is uncommon and most cases will respond well to white, yellow, and clear wormers. Clear wormers are most commonly used at this time of year. The best practice is to move cattle onto clean pasture or inside after dosing. In cases of secondary bacterial pneumonia antibiotics and anti-inflammatories should be used accordingly.

Is there a vaccine?

Lungworm vaccine may be considered if GI roundworms are less of a problem on farm but lungworm is. Lungworm vaccine should be completed before turnout. Re-infection on pasture in following years is often enough to boost immunity.

Most grazing herds will be wormed throughout summer anyway, which helps to prevent lungworm problems. In an effort to try and reduce wormer usage, lungworm vaccine may be considered along with improved grazing management.

A case study example:

A group of fattening cattle is turned out mid-May and injected with a long acting clear wormer behind the ear at turnout. This gives cover against lungworm for 120 days.

At the start of October, a few animals are heard coughing when gathered up. A couple seem slower and are looking poorly conditioned but the farmer puts it down to a touch of pneumonia starting after cold wet weather. The worst are injected with antibiotics/anti-inflammatories.

A week later, one is found dead in the field, and on post-mortem inspection, lots of adult lungworms are found in the trachea. A shorter-acting clear wormer is advised for the whole group to treat the lungworm in the animal currently. The farmer is also warned that the condition of the cattle may worsen after treatment due to a reaction to dead worms in the lungs.

This is a shortened example of what could happen within the year, if you have any concerns about your cattle please speak to your vet about the best way to treat and prevent cases.