Participants in phase two of Dairylink Ireland spoke to Sarah Campbell, veterinary advisor at MSD Animal Health, via teleconference last week. The topic of discussion was parasite control, particularly lungworm.

Sarah Campbell (left) from MSD Animal Health.

Dairylink farmers were encouraged to take a three-pronged approach to managing the respiratory parasite.

“One element is the level of immunity that our animals are developing. The second is the use of dosing and being strategic about when we use it. The other element is pasture management,” Sarah said.

Programme participants were told that the aim is to give dairy heifers enough exposure to lungworm to build immunity, while avoiding an overload that could lead to reduced liveweight gains.

Adult cows should also have some exposure to lungworm to help maintain immunity, but not too much, as it could lead to production losses through reduced milk yields.

Listen to "Lungworm control on dairy farms" on Spreaker.

“If you don’t have clinical signs of lungworms, or gutworms for that matter, I would urge you not to dose. Using a product if it is not needed will help select for resistant parasites. Plus it could also clean out carriers in your herd,” she said.

It was explained that around 20% of cows will carry lungworms without symptoms and will be a source of exposure to the rest of the herd.

“You want to keep these carriers in your herd, but if you dose animals that don’t need it, you could wipe out the lungworm in carriers and eventually immunity in the herd will drop,” Sarah said.

During the discussion, a question was asked about coughing cows that had been dosed with an eprinomectin-based pour-on (zero-day withdrawal) two weeks ago, but were still coughing.

Sarah said that the cows are most likely coughing up dead lungworms, so another dose should not be needed. Cases of heavy infection can take up to three months to clear after treatment, Dairylink participants were told.

Pasture

In general, calves are the main source of infecting pasture with parasites during their first, and to a lesser extent, second grazing season.

This means fields that are continually grazed by heifers every year become “high risk” pasture for larvae (egg) burdens for both lungworm and gutworms, so a rigorous dosing regime is needed.

“Over the years, you will end up going in with longer-acting dosing products to cover the whole grazing season, or else short-acting products will be used every few weeks,” Sarah said.

To move away from this, calves should be turned out to grass with a lower worm burden, namely ground that is not continually grazed by young stock.

The lifecycle of most gutworms is three to four weeks, and 25-28 days for lungworm

Sarah acknowledged that this is easier said than done, due to the layout of most farms. However, if possible, farmers should try to alternate the use of some fields between heifer grazing, cow grazing and silage.

“Another option is to use sheep for grazing in the wintertime, because they can help mop-up some of the worms that young cattle are susceptible to and lower the worm burden for the following grazing season,” she added.

Vaccination is an option for herds with a history of lungworm problems and is currently being used by some Dairylink participants. The vaccine is given orally before turnout, and calves can get it from eight weeks of age.

Faecal egg counts and lungworm in adult cows

Dairylink farmers were also encouraged to make use of diagnostic testing for parasite control, especially in youngstock.

Sarah recommended sending a fresh sample of dung to vets for a faecal egg count (FEC), if there are issues with coughing or diarrhoea.

“I would suggest that in the first year you do it more frequently, to get to know the pattern of infection on particular pastures. The lifecycle of most gutworms is three to four weeks, and 25-28 days for lungworm. If calves are on the same field every year, you can expect a build-up in a fairly short time,” she said.

Despite lungworm being the most common cause of coughing at grass, other health issues, such as IBR, can lead to similar symptoms.

It is important to rule out other causes of coughing so that an appropriate treatment strategy can be selected.

We need to try and increase the level of immunity that heifers have prior to coming into the milking herd

However, during the early stages of the lifecycle, the larvae of lungworm are not present in FEC, so a negative result will not always mean that lungworm are not present. It can just mean that the adults have not started producing eggs yet.

This is common in cows, as they typically retain immunity for adult stages of lungworm, so eggs are not shed in dung.

Immunity for larval (early) stages of lungworm can wane in cows, particularly over the winter period and this can still cause coughing, which will require a dose.

A common source of lungworm infection in milking herds is first lactation cows that have been subject to a rigorous dosing regime as heifers and therefore have little immunity to lungworm by calving.

These heifers can easily pick up lungworm infections themselves and then spread larvae on the milking platform through their faeces. This increases the infection pressure that cows are under and can lead to coughing and reduced milk yields.

“We need to try and increase the level of immunity that heifers have prior to coming into the milking herd, so that they are already immune and are not going to pose an overwhelming challenge to the adult herd,” Sarah said.

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