PC Sheep Scab 2020 FINAL


Sheep Scab

Plunge Dips (Pyrethroid/Organophosphate)

Wormers (Macrocyclic Lactones)

Dipping. Ensure that sheep are plunge- dipped for at least 1 minute with heads dipped under twice.

All macrocyclic lactones wormers used in the treatment of sheep scab are given by injection.

Route of administration

This varies depending on the product used. Only moxidectin has a persistence of greater than 16 days.

Most have persistence of activity of greater than 16 days.


May take several days to kill the mites present. In addition, sheep may continue to itch for a number of days post- treatment until all mite faeces has been washed off the fleece.

Speed of action

Mites normally killed within 24 hours.

Potential to contribute to the development of gut worm resistance to wormers

Their use does not contribute to increasing the risk of gut worm resistance to wormers.

Their use in the control of sheep scab can inadvertently increase the risk of gut worm resistance to wormers.

Dips require precautions for safe handling and disposal for user health and safety and to prevent environmental contamination.

Standard handling and disposal of a medicinal product applies.

Health and safety

Table 1. Sheep scab control options.

What product should I use if I am returning sheep to a pasture or shed used by untreated sheep in the previous 16 days? In this case, it is advisable to use either a plunge dip or give a moxidectin injection. Both treatments will have a persistence of activity greater than 16 days, thereby outliving any potential mite challenge. Given that the persistence of both ivermectin and doramectin is shorter than 16 days, the use of either wormer in this scenario can result in the sheep becoming re-infested as the treatment effect will have waned within the period that mites can survive off the host animal. If using these wormers, it is advised to move sheep after treatment to a mite-free environment such as an area that has been free of untreated sheep for more than 16 days. If I treat sheep that have sheep scab with an injectable wormer (e.g. moxidectin, doramectin or ivermectin) what are the additional post- treatment considerations? Sheep treated with any of these three wormers must not be mixed with untreated sheep for a period of 14 days post- treatment unless those animals will also receive treatment. This is because there is a risk of potential mite transfer from affected to non-affected sheep due to the variable speeds of action of these wormers in killing sheep scab mites.


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