Farmers should be mindful during this time of year of lungworm outbreaks, as they are hard to predict and typically arise late in summer or during autumn time.
It starts off with one or two animals struggling to catch their breadth or coughing, and if it is not nipped in the bud, it can quickly spread and affect cows within the herd.
It is often more noticeable when cattle are being moved, as they can begin to struggle with breathing. Coughing can then quickly turn into pneumonia.
When it progresses to pneumonia, some animals may take a long time to recover even after a wormer treatment, according to Animal Health Ireland (AHI).
When this occurs in dairy stock, cows can show a drop in milk yield during the outbreak.
Lungworm
Young calves that are on their first season of grazing are most susceptible to pick up lungworm so calves should be closely monitored for any clinical signs.
Paddocks that were grazed by calves the year before are at a higher risk of contamination due to over-wintering of larvae.
Animals that have a lungworm infection may have an increased susceptibility to other respiratory infections, which can be problematic for calves if they are already under stress at transport, castration or going into housing.
The risk assessment of different pastures at spring and mid summer as per AHI are as follows:
Time High risk pastures Medium risk pastures Low risk pastures Spring Grazed by young calves in the previous year.
Grazed by lungworm-infected cattle in the previous yearGrazed only by cows or yearlings with no history of hoose in the previous year New pasture.
Grazed by sheep or used for hay or silage only in the previous yearMid-summer Grazed by young calves in the spring Grazed only by cows or yearlings with no history of hoose Grazed by sheep or after grass (used only for silage or hay in the first half of the season)
Dung samples can quite often lead you astray, as a negative test does not rule out a lungworm infection as at the immature larval stages of the worm, it can cause clinical signs before they are present in the dung.
Cattle develop immunity to lungworm in their second or third season at grazing if they have received adequate exposure to the worms.
However, this immunity can be short lived and will wear off over time if they are not exposed again which can lead to cows developing clinical signs.
After a long housing period, cows should be given a long acting wormer to prevent the natural boost needed to maintain immunity.
Clinical signs
More and more cows have been showing clinical signs of lungworm and it could be because they did not get sufficient exposure as young stock to develop enough immunity.
This could be due to the fact that they were never raised on paddocks with lungworm infection or following intensive anthelmintic treatments.
Animals like these will develop typical signs along with a patent infection where larvae might be detected in dung samples.
If there is limited follow up exposure to the lungworm, cows may develop clinical signs as immunity eases off, whereas high pasture lungworm burdens may overwhelm the animal’s immunity and result in reinfection syndrome.
Reinfection syndrome may result in respiratory diseases and a drop in milk yield and clinical signs and tissue damage can be severe in these animals.
Where lungworm is a repeated problem, vaccination should be considered and given to calves and yearlings before the grazing season.
Spring-born calves will need two vaccine doses before turnout and anthelmintic treatments can interfere with vaccine effectiveness when given at or before vaccination.