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Lungworm poised to strike grazing cattle

Insufficient immunity is increasing cases of lungworm in cattle, and this season is providing the perfect conditions for autumn outbreaks of disease, according to vet Claire Whittle.

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Lungworm poised to strike grazing cattle

Lungworm disease, also known as husk or hoose, is a serious respiratory disease which results in long-term losses in cattle productivity.

In young calves, growth rates can be reduced by more than 20 per cent (1) and the cost of losses in production due to poor growth can average £50-£100/head2 .

In adult dairy cows, milk yield can be reduced, impacting herd profitability by about £3/cow/day (2).

Cattle which either fail to develop immunity to lungworm as young animals, or which do not receive an annual immunity boost as adults, are at high risk of developing disease.

 

Perfect storm

 

According to Claire Whittle, veterinary surgeon at LLM Farm Vets, this year is developing into a prime candidate for high levels of lungworm disease in late summer and autumn, and she is urging farmers to prepare to act fast to control disease outbreaks.

Claire, who covers livestock farms in Shropshire and the surrounding areas, says: “We are seeing changes in seasonality of lungworm disease, with outbreaks coming earlier and later in the grazing season than we used to expect.

 

“Typically, these can now occur from July onwards, but last year was particularly bad and we even had a case in May.” Lungworm infectivity is driven by the weather, with warm and wet conditions increasing the likelihood for infection.

The timing of turnout in spring and the climatic conditions during the grazing season have an impact on the ability of lungworm larvae to reproduce and infect cattle.

Claire says: “Lungworm larvae on pasture do not survive for long when it is hot and dry.

This year, the mainly dry spring conditions have kept challenge levels low.

“However, this means adult cattle have not received an annual boost to their existing immunity, and calves and youngstock are not receiving any early season challenge to help them build immunity.

“Rainstorms after this dry period will allow lungworm larvae to be released from dungpats and rapidly infect the pasture.

With potentially low levels of immunity in cattle this year we expect to see significant disease outbreaks in late summer and early autumn.”

 

Management

 

A fine balance needs to be struck between allowing cattle some exposure to lungworm at grass to build or boost immunity, while preventing high challenge situations which will result in disease.

Claire says: “Vaccination before turnout provides rapid onset immunity.

It is a good option, especially for young cattle during their first year at grass, and for all cattle on farms with a known lungworm population.” Alternatively, allowing cattle to receive a low dose challenge during each grazing season allows them to build long-lasting immunity to lungworm.

However, this needs careful management to ensure increasing challenge does not result in clinical disease.

Claire says: “Assess the risk to groups of animals based on their grazing history and any worm treatments given over the past and current season.

“If cattle have not had sufficient exposure to lungworm over the early grazing period, the risk of disease will remain high, potentially until housing time in areas with milder weather.” She warns that loss of immunity could be a particular problem this year.

“The unpredictable nature of lungworm means sudden high challenge late in the year can overwhelm any immunity gained early in the season, even from vaccination.

“Weaned suckler calves and dairy heifers require particular attention, since even if they acquired some immunity at grass the previous season, this wanes during housing.

“They are effectively naive again at turnout, and this year’s dry spring with limited exposure will compound the problem.”


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 Claire Whittle
Claire Whittle

Diagnosis

 

Lungworm is usually diagnosed by clinical signs. Claire says: “We usually err on the side of caution with lungworm.

Diagnostic testing to identify larvae, rather than eggs, in dung can be useful, but we mainly rely on animal history and observed symptoms to determine infection.” Cattle with a lungworm infection will typically have a deep harsh cough, most noticeable when they are moving, and their breathing may be laboured.

As the lungworm burden increases, individuals may cough at rest and, in severe cases, cattle may salivate excessively and adopt an ‘air hunger’ position with head and neck extended, and their tongue stuck out each time they cough.

Increased resting, reduced grazing, weight loss and sudden milk drop may also be seen, especially in adult or lactating cattle.

Up to 10 per cent of animals may be sub-clinical carriers of lungworm (3), which means they may not show signs of disease, but they will carry adult lungworms and contribute low numbers of lungworm larvae to the pasture.

In effect, they are the silent spreaders of disease.

Claire says: “Treatment is usually given to the whole group to ensure animals with infection but not yet showing clinical signs are treated and do not become carriers.

In severe cases, individual animals may require antiinflammatory pain relief and additional supportive treatment.

“Secondary bacterial infections may also be present due to the lung damage inflicted by the worms, and in these cases antibiotic treatments may be required.”

 

Lasting damage

 

Unfortunately, once cattle have experienced lung damage from a lungworm infection, the impact is long-lasting and the animal will never be as productive as those which were unaffected.

Financial losses will likely be hidden in slower growth, later bulling and lower milk yields Lung damage can make cattle more prone to respiratory infections later in life, long after the lungworm has been treated.

High stress events, such as calving, can prompt the return of pneumonia symptoms which will further reduce a cow’s productive potential. “Prevention is key,” says Claire.

“Vaccination and a risk-based approach to worming at grass can help protect cattle from disease, while allowing them the opportunity to gain long-lasting, effective immunity.” Although widespread, lungworm is not yet present on every farm.

Farmers should avoid importing it wherever possible, by quarantining and treating bought-in cattle.

This will prevent exposing the home herd, which may be completely naive to lungworm and reduce the likelihood of a severe outbreak.

References:

  1. COWS (2017) Make lungworm control a priority this spring [online] Available at: cattleparasites.org.uk/app/uploads/2018/04/Make-lungworm-control-a-priority-this-spring.pdf [Accessed May 29, 2020].
  2. COWS (2020) Control of lungworm in cattle [online] Available at: cattleparasites.org.uk/app/uploads/2020/01/lungworm-231219.pdf [Accessed May 29, 2020].
  3. Eysker M, Classens EW, Lam TGM, Moons MJ, Pijpers A (1994) The prevalence of patent lungworm infection in herds of dairy cows in the Netherlands. Veterinary Parasitology 53 (3-4) 263-267.

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