12 April 1996


With sheep scab and lice on the increase and a wider choice of treatments available, Peter Bates of the Central Veterinary Laboratory advises producers to read the instructions on the label carefully before treating their flocks. Its better still to do it before buying a product for scab control

LABELS should state whether a product is effective against sheep scab and whether it protects against reinfestation as well as cures active scab.

Length of protection against scab varies with the product and with the fleece length. Different products contain different insecticides. The constituent insecticide and its percentage concentration (active ingredient) will be shown clearly on the label.

If the label states that the dip contains one of the organophosphate (OP) insecticides (diazinon or propetamphos), or the synthetic pyrethroid (SP) insecticide flum-ethrin, then the dip was approved prior to the deregulation of scab in 1992.

Approved dips will guarantee at least three weeks protection against scab with a fleece length of 1cm (0.4in). In reality the length of protection will be considerably longer on fully fleeced sheep. The sheep scab mite can live off the sheep (on fences, tags of wool, straw bedding) for between 15 and 17 days. Consequently sheep dipped in one of the approved dips can be returned to the infested pasture, yard or barn, directly after dipping without the risk of reinfestation from the environment. Fully fleeced sheep will be protected against reinfestation on common grazing for at least 10 weeks.

Dip formulations not containing diazinon, propetamphos or flum-ethrin, licensed after 1992 and consequently not undergoing the rigorous approval testing in force when sheep scab was notifiable, may not protect as long as approved dips.

Sheep dips currently in this category contain the synthetic pyre-throid high cis cypermethrin.


Systemic endectocides (effective against both scab mites and parasite worms) administered by injection (such as MSD Agvets Ivomec for sheep) offer little protection against reinfestation. If these products are used, sheep should not be returned to infested accommodation or grazing directly after treatment. They should be kept in clean accommodation for at least three weeks before returning to infested pasture.

None of the currently available pour-ons are effective against scab, and their use could induce resistance to other synthetic pyrethroid products, making the disease more difficult to eradicate from a flock. It is important that the parasite present within the flock is professionally identified and the most effective treatment prescribed.

Failure to follow product in-structions can cause incomplete control of scab and the potential for further treatments to be less effective against the residual mites. This would make it more difficult and more expensive to control the disease. There have already been two cases of scab mites resistant to flumethrin in the UK. Let us stop resistance spreading.n


In the early stages of sheep scab, sheep will be restless and rub themselves against fence posts and gates leaving a broken fleece. In the later stages rubbing and head tossing become more excessive, areas of wool loss appear and infected sheep may go into a possibly fatal epileptic fit.

If you suspect scab, first get it confirmed by your vet. They will take samples of wool and scab and look for scab mite under the microscope. If scab is confirmed (and not lice) the choice of treatments is either dipping or ivermectin.

The WHOLE flock and not just the affected sheep or group must be treated.

Sheep ectoparasites

Effective against



OP dipsDeosan diazinonDeosandiazinon*****

Diazadip Bayer*****

Cooper fly andMallinckrodt*****

scab dip

Golden fleeceBimeda*****

Paracide +Battle Hayward

& Bower*****

Summer fly dipBattle Hayward

& Bower*****

Youngs bioticYoungs*****

Neocidal winterCiba*****

Flyte 1250Youngspropetamphos*****SeraphosCrown****

Ectmort CentenaryYoungs*****

Summer dipYoungs****

SyntheticCrovect dipCrownhigh cis-*****

pyrethroidCrovect pour-onCrowncypermethrin****


Provinec dipC-Vet*****




Parasol pour-onCiba****

Spot onMallinckrodtdeltamethrin*****


Avermectin<Ivomec inject.MSD Agvetivermectin***

Oramec drenchMSD Agvet*


OtherVetrazine pour-onCibacyromazine*


< Also control larval stage of Oestrus ovis (nasal bots)


Only dips containing organophosphates (OP) (diazinon or propetamphos) or the pyrethroid flumethrin are scab approved.