Pasture larval contamination approaches annual peak

The July NADIS Parasite Forecast, sponsored by Merial Animal Health, warns that the months of July and August will bring a peak in larval contamination on pastures.


Profuse diarrhoea affecting a yearling Holstein heifer at grass during September

The July NADIS Parasite Forecast, sponsored by Merial Animal Health, warns that the months of July and August will bring a peak in larval contamination on pastures. Wet summers are often related to an increase in gutworm burden and farmers are advised to check stock regularly.

In cattle the incidence of type 1 Ostertagiosis peaks in late summer. Symptoms include sudden profuse scouring which will quickly affect much of the herd. Lynda Maris Brand Manager with Merial Animal Health says: “There are a number of products on the market licensed to treat gutworms, for example Ivomec® Classic Pour-on and Eprinex®. Many of these products also provide persistent activity to protect against re-infection and allow dosing intervals to be increased. The length of persistent activity provided can vary between products and hence the dosing intervals will also vary. Farmers are advised to check product packaging and follow appropriate recommendations”.

The NADIS Parasite Forecast also highlights the risk of lungworm in cattle this month. Lynda says, “Some anthelmintic treatment regimens may not last the whole grazing season. Lungworm infection may therefore be a problem towards the end of summer, especially if conditions are wet, allowing larvae to be released from dry dung pats”.

Initial signs of lungworm infection include coughing during exercise and at rest, an increased respiratory rate, and cattle rapidly losing weight and condition. Mrs Maris advises that if symptoms are observed, farmers take prompt action and treat all animals in the herd.  She says the reason why all animals should be treated is that although not all cattle may be coughing, others in the same group may have suffered lung damage without showing obvious symptoms of the disease. Prompt action is required to avoid permanent damage to the lungs leaving animals susceptible to secondary infections and affecting long term productivity.

In sheep the effect of persistent anthelmintic treatments that were administered to ewes at lambing may now be wearing off. Farmers should check whether ewes need re-dosing by carrying out faecal egg counts. Mrs Maris says: “ Farmers should also remember  to include rams in their parasite control programme as they are often forgotten, but equally susceptible.”

‘Safe pastures’ (grass that has not been grazed by sheep this year) and post-silage fields may be best for fattening weaned lambs as any worms on these pastures will have died without the presence of a host. Mrs Maris says: “If producers are able to put fattening lambs on silage fields once cut, around 10 per cent of the strongest lambs can be left untreated to carry an amount of anthelmintic-susceptible worms over to the fresh pasture. This can help to avoid selection for resistant strains of worms”.

If there is no option but to keep lambs on contaminated pastures, an anthelmintic treatment may be required to limit the population of worms and therefore the severity of PGE (Parasitic Gastro- Enteritis).

Blowfly strike is a major risk at this time of the year. In addition to dips there are several topical products on the market which will prevent blowfly strike for a number of weeks. Farmers are advised to check the weeks cover provided and select the most appropriate product for their situation.  Shearing will provide a degree of protection from strike but this is short term and particular attention should be paid to any lesions caused by shearing as these will be very attractive to flies.

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