Lungworm in cattle and deer

We have had some reports in the lower North Island of lungworm in both deer and cattle this past autumn. This is most likely attributable to ideal conditions favouring larval development on pasture, and perhaps due to lower residual pasture covers on some properties leading to higher intakes of larvae.

Lungworm in deer is caused by a deer-adapted lungworm Dictyocaulus eckerti. Cattle lungworm, Dictyocaulus viviparus, has also been shown to affect deer, although it is less well adapted to red deer.

In the lower North Island, clinical disease in dairy calves is common and is often associated with higher stocking rates and where there are separate grazing regimes for both young and adult dairy stock. High levels of worm resistance establish quickly in animals exposed to small larval challenges. Disease in yearlings and adult cattle is therefore rarely seen probably because of continuous exposure to challenge on pasture. 

Some larvae will overwinter on pasture, but most will survive the winter by becoming inhibited in the animal’s gut and later resuming development in the spring. The result is that the earliest born calves in the spring become infected and contribute more larvae to the pasture over the summer and autumn. Later-born calves (and those born in the autumn) are therefore exposed to an increased concentration of larvae on the pasture when they have not yet developed immunity resulting in outbreaks of coughing calves in autumn and winter.

Deer weaned in the autumn are most susceptible to infection because they have also not yet developed immunity and because the environment in the autumn favours survival of the parasite. Adult deer are somewhat resistant, although disease can occur in situations of stress or poorer nutrition. Sudden death may be the first sign although weaners will sometimes lose condition, develop a roughened coat, and have a soft cough. Heavy lungworm burdens are obvious at post mortem.

Routine drenching for gastrointestinal parasites will usually remove lungworm as this parasite is generally susceptible to modern drenching regimes. However, it should be mentioned that levamisole (present in all combination oral drenches) is not effective in deer (unlike cattle) because of the rapid rate it is metabolised by deer.

Please feel free to talk to your TVL veterinarian if you have any questions regarding drenching against lungworm and/or parasite management and control.

 

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