Dairy cows grazing grass

Dosing Advice: Combating Lungworm In Your Herd

Author: James O’Neill 


Lungworm infections in your herd can cause a severe and often fatal disease that is commonly called hoose. A lungworm infestation is caused by exposure of grazing animals to lungworm larvae on a pasture. The lifecycle of the lungworm is about four weeks long i.e., from the ingestion of larvae to the excretion of infective larvae by the affected animal. In the worst case, within four weeks of ingesting lungworm larvae, the cow or calf can be shedding millions of fresh larvae onto the pasture via their faeces and is most commonly seen from August to October.

Lungworm: Spotting The Early Signs

Early signs to look out for include coughing, initially after exercise and then at rest, with an increased respiratory rate. Left untreated, cattle will often lose weight, with noticeable deterioration taking place in their body condition. Dairy cattle may also experience a sudden and dramatic drop in milk yield.

Rain can disperse larvae in contaminated faeces, while warm, moist conditions keep infective larvae alive and encourage fungal growth. Larvae often make use of the fungal spore, Pilobolus (found on cattle dung), to disperse themselves on a pasture. Generally, conditions that favour the growth of pasture also favour the development of the infective larval stage L3, which is why outbreaks peak in late summer and early autumn. A dry season followed by a damp one has always encouraged outbreaks as this creates a natural immunity gap.


Treat infected cattle as early as possible because there may be varying degrees of infection in any one group. Levamisole (Levafas Dimond) and white drenches (Tramazole) will take out what parasites are there on the day of treatment and have no residual effect. Macrocyclic Lactones such as Ivermectin (Acomec Pour-On, Ivomec injection and Eprizero Pour-On) will give longer protection (28-120 days is typical). The product used will have a bearing on subsequent grazing management post-treatment. Calves that were heavily infected need to be closely observed for 1-2 days post-treatment.


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