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Dairy Cattle

LUNGWORM

Lungworm (Dictyocaulus viviparous) is most likely to be seen from June onwards with a peak in September/October. Occasionally cases are seen until January. Lungworm follows the same lifecycle on the pasture as Ostertagia but inside the animal there are major differences to the larvae’s development (see picture). This lifecycle can take as little as 10 days, stressing the importance of prevention as large numbers can build up in a very short period of time. Lungworm larvae on the pasture can be spread by a fungus found in the dung pats, which explodes to spread its own spores and the lungworm larvae along with it. Development of larvae occurs particularly during warm wet weather in the summer.

 

Clinical signs

Early clinical signs in growing cattle (and dry dairy cows) include an increased respiratory rate at rest, but more noticeable, frequent coughing especially after short periods of exercise. Severely affected cattle may be reluctant to move, stand with their head down, neck extended, and cough frequently. Disease can severely affect growth rates so much so that some farms have documented increased time to reach fattening weight of 22 weeks. The cost in loss of production can far outweigh that from mortality.

In the dairy herd, a reduction in bulk tank is noted along with frequent coughing when cows are walking to and from the milking parlour. With very large larval numbers on pasture, disease can occur in adult cattle vaccinated as calves but not subsequently challenged for several years and deaths can occur as a result. Lost milk production could reach £1.50 to £3 per head per day with recovery taking 10 to 20 days after treatment.

Diagnosis

Diagnosis of patent lungworm infestation is based upon the demonstration of lungworm larvae in the faeces. Antibody testing of blood can give an idea of previous exposure to lungworm (although timing of exposure is hard to pinpoint) and bulk milk testing can give an idea of herd level exposure.

Prevention

Lungworm prevention is based upon development of immunity and is best achieved by vaccination (Huskvac). Cattle are naturally exposured to lungworm (and other parasites) during the grazing season during which time immunity develops and infection can then be controlled by strategic anthelmintic treatments. This however is a very risky strategy for lungworm prevention but would control PGE in most situations. Therefore, PGE is often a secondary consideration to the more important lungworm disease. Most available wormers will kill lungworm.

Where vaccination of cattle for lungworm is undertaken planned anthelmintic treatments for PGE must be considered so as not to interfere with the vaccine, which involves dosing with live but inactivated lungworm larvae. Most wormers will kill the vaccine larvae rendering it ineffective. Poor exposure during their first grazing season at pasture and failure to develop immunity renders cattle susceptible to lungworm during their second season at pasture especially if weaned beef calves graze the same fields every year (for example rented ground away from the main farm etc).