With reports of rising lungworm infections in cattle in recent weeks, vet Emily Francis offers some advice on protecting your herd and profits.
Over the past few weeks an increasing number of lungworm infections in cattle have been reported.
Vet Emily Francis, of Westpoint Farm Vets in Winchester, says outbreaks seen in late summer/early autumn are typically in unvaccinated youngstock.
“This is because the life cycle of the parasite occurs quickly in warm and wet conditions and eggs dropped by carrier animals earlier in the season will have developed multiple times causing a high larval pasture contamination on heavily grazed pastures by this time of year.
“Although this year could be considered a risky one due to the warm weather and recent rainfall, outbreaks are very difficult to predict and dependant on many factors including weather conditions, immune status of the grazing animals, time of year, grazing history of the pasture and the farm’s use of anthelmintic.”
A parasitic infection of the respiratory tract in cattle, lungworm can cause coughing and respiratory distress. Death can occur in heavy infestations. Other signs can include weight loss and reduced milk yield in dairy cows.
While outbreaks are unpredictable, they are most likely to occur in animals which have not yet developed good immunity to the lungworm parasite as immunity develops over time with a low but persistent exposure to the parasite needed for this to occur, says Ms Francis.
She adds: “Immunity develops in two ways, either to the larval stages, which lasts four months, or to the adult worms in the lungs, which last up to two years.
"Animals require frequent exposure to the parasite for the immunity to remain during its lifetime and to prevent clinical disease occurring.”
Thought to be most at risk, Ms Francis says, are unvaccinated youngstock which have not yet developed an immune response grazing heavily contaminated pastures during late summer and autumn, when levels of larvae on the pasture are high or when anthelmintic protection has waned.
She says: “These outbreaks are less common as control of parasitic gastroenteritis with long acting anthelmintics or the use of the lungworm vaccine has become common practice, however they are still seen.”
Farms which have a known lungworm population and are not doing so already, Ms Francis says, should consider immunisation with lungworm vaccine.
She adds: “The best method of preventing parasite bronchitis in ﬁrst season grazing calves is immunisation with lungworm vaccine.
“The vaccine is given orally to calves aged eight weeks or more. Two doses are given four weeks apart and cattle should not be turned out until two weeks after the second dose.
“It is crucial that vaccinated animals are not treated with anthelmintics at turnout as the vaccine relies on natural infection.”
Vaccination may be more difficult in calves on spring-calving or all-year-round calving herds, Ms Francis says, so control of parasitic bronchitis in calves can be achieved by use of prophylactic anthelmintic regimes either by strategic early season treatments or by the administration of rumen boluses.
“As natural immunity will not have developed due to rigorous control in the ﬁrst grazing season, exposure to lungworm larvae may be so limited that cattle remain susceptible to infection. In such situations, it is advisable to consider vaccination prior to the second year at grass or before heifers are added to the main herd.
“Prevention in adult cattle includes treatment and quarantine of bought-in animals and avoiding whole herd anthelmintic treatment.”
In low-prevalence regions of lungworm disease or on farms with no previous history of lungworm, preventative vaccination is not necessary, Ms Francis says. In such herds, a policy of preventing the introduction of infection should be rigorously enforced by good quarantine measures.
In terms of treatment, all available anthelmintics are highly effective against developing fourth-stage larvae and adult parasites.
Ms Francis says: “To date, there are no conﬁrmed resistance issues. Affected cattle should be treated as early as possible for best results.
“Animals with a mild cough should show a rapid response to treatment and should be removed from the contaminated pasture. Those in respiratory distress should be treated under veterinary advise and monitored
closely,” she adds.
When it comes to diagnosing lungworm Ms Francis says: “Post-mortem is the gold standard as the adult worms can be viewed in the airways.
“Dung samples can be checked for lungworm eggs, but samples have to be very fresh and processed quickly to be reliable.
“Checking for antibody levels in bulk tank samples is not massively reliable as results are only positive when more than 30 per cent of animals infected and this is rarely the case.
“ELISA tests on blood or milk samples in a proportion of adult animals or first lactation heifers tends to be more reliable. Some vets can perform a broncho-alveolar levage to look for larvae in the airways.”