11 April 1997


Different pour-on anti-parasiticides require specific application techniques to best counter their target parasite. Jonathan Riley reports

UNLIKE systemic pour-ons for warble fly, the products used to control lice, ticks, blowfly and head fly, rely on blending with skin secretions to transport them across the surface of the sheep, says MAFF parasitologist Peter Bates, of the Central Veterinary Laboratory, Weybridge.

"Within 24 hours the chemical has moved outwards from the site of application across the entire sheep.

"But some areas of the sheep are better covered and protected than others depending on the level of skin secretions and their distance from the site of application," says Mr Bates.

"This could mean that some parasites do not receive a full dose of the chemical – allowing them to reinfest the flock or increasing the likelihood of resistance to the chemical applied.

"It is also vital to establish which parasite is present to use the most effective chemical to control it, and to time the treatment to provide protection against the parasite when it is most vulnerable."

Lice are harboured in the sheeps flanks and the limb pits, so for lice Mr Bates suggests the best control is achieved by delivering the chemical from the base of the neck to the pelvis.

Ticks are also found in these areas but picked up as the sheep grazes and, therefore, inhabit the neck too, so care must be taken to ensure that chemical is applied from the base of the head and down the spine.

Protecting against blowfly strike requires an additional sweep of chemical applied in an arch across the breach which is where 60% of fly strike occurs.

Most products are applied down the spine but in MAFF-funded trials at the CVL, it was found that it is virtually impossible to apply the product accurately down the spine in a practical situation.

"All operators contributing to the trial applied products slightly to one side of the sheeps spine. The spine, therefore, acts as a ridge that the chemical has be transported over in order to cover both sides of the sheep.

This means the chemical moves more easily down one side of the sheep leading to an uneven coverage.

"We, therefore, recommend that pour ons should be applied not in a straight line but in a zigzag down the length of the spine which helps to spread the coverage evenly.

"We also found considerable differences in the level of coverage of different sheep breeds because the chemical not only moves across the sheeps surface but out into the wool. This means sheep with longer staples should have more chemical applied as a greater quantity moves away from the skin and into the wool," says Mr Bates.

"Applying the correct amount of chemical is vital to ensure adequate coverage to kill parasites. Lambs should be divided off and treated separately while the heaviest ewe is weighed. The equipment used should then be calibrated for the whole flock with enough chemical to treat this ewe.

"When treated ensure the animal is clearly marked because treating twice is a waste of money and missing an animal out leaves the unprotected sheep both vulnerable and as a harbour for parasites which can then reinfest the flock," he adds.n

Protecting against blowfly strike requires an extra sweep of chemical applied in an arch across the breach.


&#8226 Less hazardous than dipping.

&#8226 Less labour intensive.

&#8226 Easier chemical disposal.

&#8226 Less stress for animals.


&#8226 Identify parasite.

&#8226 Follow instructions for protective equipment.

&#8226 Zigzagging down the spine improves coverage.

&#8226 Adapt application to control particular parasites.

&#8226 Divide flock and use enough chemical to treat the largest animal.

&#8226 Mark sheep as they are treated.