Weather conditions may offer perfect environment for lungworm to develop
After a few weeks of dry and warm weather, the recent rainfall may have created the perfect environment for lungworm development.
Lungworm, also known as 'hoose', is a respiratory disease caused by the roundworm parasite Dictyocaulus viviparous and usually thrives and multiplies in humid conditions following rainfall.
As the last couple of weeks have been dry, many animals will have experienced low levels of worm burdens thus far. However, with rainfall over the last week expected to continue into next week, vigilance is key.
An infection starts off with one or two animals struggling to catch their breadth or coughing, and 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.
Lungworm
Lungworm has a number of phases. Adult lungworms live in the lungs and lay eggs, which are coughed up and swallowed. Older animals such as yearling or adults may serve as carriers over the winter, as some adult worms will survive in the lung.
These eggs will then hatch and develop into stage one larvae as it is passed through the intestine before being released in the dung, where the larvae will then develop in stage three in the dung pat.
When rain falls, or through the aid of the fungus Pilobolus spreading its spores, the splashing effect helps the stage three larvae travel from the dung pat up the grass plant, ready to be ingested by the animal.
Once ingested, the larvae is passed from the intestine to the lung and grow into adult worms, piercing their way through the intestinal wall to move into the blood and lymphatic system to get to the lungs.
It may take up to 24-28 days from the larvae being eaten to the passing of eggs but if the weather is warm, up around 20℃ and humid, infectious larvae may be available on pasture within seven days, according to Teagasc.
Young calves that are on their first season of grazing are most susceptible to pick up lungworm, so they 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.
The risk assessment of different pastures at spring and mid summer as per Animal Health Ireland (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 year Grazed 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 year Mid-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)
So, symptoms normally are seen in young cattle in their first grazing season, typically in the latter part of the summer.
Symptoms will vary depending on the number of larvae ingested and on the animals immune response, but are as follows:
Mildly affected animals will be coughing on and off, especially after exercise;
Moderately affected animals will cough regularly at rest and have an increased respiratory rate;
Severely affected animals will have difficulty breathing and may adapt a stance where the head and neck stretch out, mouth is open and the tongue hangs out;
Lung damage can be severe and the damage can sometimes be irreversible, so mortality can occur despite the removal of worms with an anthelmintic;
In milking cows, it can cause a severe drop in milk yield and this can occur before coughing;
The problem is that when cows are affected, they are more susceptible to other respiratory pathogens such as viruses and bacteria.
If a lungworm infection has been identified, treatment with one of the three classes of anthelmintic (white, yellow, clear) will be required.
Treatment of the whole group should be done quickly after the appearance of clinical signs in order to limit the impact of the infection.
If lungworm treatment gets delayed, lung damage may become severe and be untreatable and if heavy infections of lungworm are suspected within your calves or in your herd, your vet should be contacted to seek advice before treatment.
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