The impact of lungworm should not be underestimated, says Dave Armstrong, national veterinary manager with Zoetis.
He explains a lungworm burden can result in a milk production decrease, a reduction in fertility and an extended calving period.
He says: “Lungworm has a mortality rate of 1-7 per cent, although it is likely that sub-clinical infections could be of far greater economical relevance.”
According to Dr Armstrong, the disease has an impact economically because of both the direct and indirect costs.
Losses in a bad lungworm outbreak in growing cattle can average between £50-£100 per head, with a potential loss in milk production of £1.50 to £3 per head per day. Recovery can take between 10 and 20 days post-treatment.
He explains the lungworm itself, in its ‘adult’ form, is slender and threadlike, measuring 4-8cm in length.
He says: “Lungworm in cattle can cause an infection of the respiratory tract, which is commonly known as husk, a common respiratory disease in cattle.
“Lungworm is more commonly seen in the first-year grazing cattle in late summer and early autumn. However, there is an increase in it being reported in older cattle.”
He explains that cattle become infected by eating grass with contaminated infective larvae.
Once ingested, the larvae then migrate to the lungs where they develop into adult lungworms, before producing eggs. The larvae travel up the trachea, are swallowed and eventually pass out in the faeces.
“The larvae further develop in the faeces, then after a week or less, move onto the grass, either with the help of rainfall, or by attaching themselves to spores of the fungi, Pilobolus, before the lifecycle starts all over again,” he says.
Dr Armstrong adds the complete lifecycle of lungworms takes a minimum of about four weeks – one week on pasture, three weeks in the animal.
LUNGWORM can be very unpredictable, so a health plan from your veterinary surgeon is a great place to start, says Dr Armstrong.
“The best method of prevention is to vaccinate youngstock, by using a live vaccine. This is given as two separate doses at six weeks and then two weeks prior to turn out.
“If lungworm is considered an issue on your farm, then it may be advisable to vaccinate prior to the second year at grass,” he says.
All incoming cattle should be treated and quarantined, not just for lungworm, but also for fluke and other worms.
Dr Armstrong says: “Most anthelmintics which are used for the control of gut worm will also work against lungworm.
“Anthelmintics can be used in first year grazing to prevent a build-up of lungworm larvae on the pasture, with worming done two to three weeks prior to housing.”
THE risk of disease depends greatly on the level of challenges and factors, these include:
1 The farm history. This can be a reliable indicator that the farm may face future challenges, as larvae can survive for a long time on the pasture
2 Humidity and rainfall. Water can disperse larvae in contaminated faeces, while warm moist conditions keep the infective larvae alive, encouraging fungal growth
3 Replacement stocks. The introduction of replacement stock can destabilise a herd’s balance of immune and susceptible animals.
Diagnosis is usually based on the clinical signs of the cattle and the grazing history. The main test used to confirm lungworm disease is by detecting the stage one larvae in faecal samples using the Baermann technique.
However, a low number of larvae or negative larvae counts do not exclude lungworm, as the cattle may be in a prepatent or post-patent phase, or may have previously been exposed, also known as the re-infection syndrome.
DR Armstrong says all available anthelmintics are very effective against developing fourth stage larvae and the adult lungworm.
He says: “Currently, there are no reported cases of resistance to anthelmintics. All affected cattle should be treated as early as possible. Remember, some animals may not respond immediately. Signs may be worsened by dead larvae blocking the lower airway.
“Those animals which are coughing and showing signs of laboured breathing are normally in the prepatent stage of the disease. Using an anthelmintic should result in the animals making a good recovery. Cattle which are showing these signs should not be returned to grazing/the source of the infection.”
Unfortunately, some cattle show more severe signs of lungworm and Dr Armstrong says these should ideally be kept in for treatment and observation.
“Despite animals being treated with an anthelmintic, a small proportion may not recover. Severely affected cattle may need antibiotics, anti-inflammatories and hydration, should they not be drinking,” he says.