Dairy and beef farmers are being warned to remain vigilant for signs of coughing in all ages of cattle at grass, as recent warm, moist weather is expected to lead to a mass hatch of lungworm larvae.
Already the National Animal Disease Information Service (NADIS) has reported several cases, with the Vet Lab Agency also predicting more cases as the recent rainfall breaks up dry faecal pats.
“Although few cases of lungworm have been seen so far this year, the recent rainfall could encourage lungworms to complete their lifecycles thus potentially causing disease outbreaks to develop in to the autumn,” explains VLA vet investigation officer, David Harwood.
And because the moisture has not been there this summer to hatch the eggs, numbers have not only built up, which will cause a rapid increase in pasture infectivity given correct weather conditions, but low levels of infection may also mean natural immunity may not have built up, says vet Maarten Boers, The Livestock Partnership.
“Dairy and beef farmers must remain vigilant over the next couple of weeks, even when animals were vaccinated earlier in the season. This is because immunity from the vaccine alone only lasts for three to four months. And when animals weren’t exposed to low levels of natural infection during this time, they could now be susceptible to infection.”
Ideally in this situation, farmers should give a booster vaccine, but in reality because of practicalities and costs, Mr Boers says many farmers may be looking at alterative strategies. “Worming may be one option, but each case needs to be taken on an individual basis, as over worming could remove all lungworm challenge, which will remove the low level of infection needed for natural immunity.”
And for this reason, it’s not just young stock or first season grazers that are susceptible to infection, says Moredun Research Institute’s Jacqui Matthews.
“All animals that have not been vaccinated or exposed to low levels of infection during their first grazing season are susceptible. Even when animals have been vaccinated they require further boosting via field challenge to remain immune. So when older animals have not been exposed, for example, when they have been housed for several grazing seasons, they are just as susceptible as first season grazers. Vaccination is however, the most effective way to protect livestock.”
But any farmers thinking about alterative control strategies, such as worming for lungworm should think carefully before doing so, says vet Andy Biggs, The Vale Vet Group. “When wormers are used to blanket treat cattle this puts pressure on resistance. Looking at pasture availability and knowing the pasture grazing history can help farmers assess the risks and areas of pasture that may be of lower risk.”
As a result, cattle of any age coughing or showing respiratory signs when at grass should be suspected of having lungworm and treated immediately, says Steve Borsberry, 608 Vet Group. “Cows showing signs need to be wormed immediately as 2-3000 parasites are enough to kill animals and clinical symptoms can develop within one week.”
But farmers need to be strategic in the wormers they use to treat clinical cases, adds Bishopton Vet Group’s Jonathan Statham who has treated several cases in his practice already this month. “A yellow wormer (levamisole) is the safest option to avoid overkill in clinical cases. Farmers also need to be on the look out for secondary infection such as pneumonia and IBR triggered by initial damage from lungworm.”