Farm Ireland

Monday 19 March 2018

Keep dipping to control outbreaks of sheep scab

Sam Wilson looks at his pen of rams at the Donegal Suffolk Breeders' show and sale at Raphoe Livestock Mart
Sam Wilson looks at his pen of rams at the Donegal Suffolk Breeders' show and sale at Raphoe Livestock Mart

Peadar O Scanaill

As vets, we always keep an eye out for interesting disease occurrences in Britain and in our northern European neighbours. An outbreak of sheep scab in northeast Scotland caught my attention recently.

Sheep scab is a skin parasite that gets a lot of attention but not too much detail whenever it emerges. It is a notifiable disease which means we must inform the Department of Agriculture whenever we suspect or diagnose the disease.

Sheep scab is caused by a parasitic mite Psoroptes Scabii Ovis that feeds on sheep skin. It is a tiny mite with eight legs and two large biting jaws that penetrate the skin. The mite lives off the blood and lymph that oozes out of the bites.

A few interesting points with sheep scab is that an egg can hatch and grow and begin to lay more eggs in as little a time as nine days. One female mite will lay up to 90 eggs and live for up to 30 days on the sheep's skin. They love warm moist conditions and as the winter fleece thickens and the wetter autumn days approach, the fleece becomes a haven for mite development.

The parasite spreads by contact and can only be spread in two ways. One is close contact with an infected sheep or direct contact with any contaminated equipment.

This means that control is based on preventing infected sheep entering the flock or contaminated material coming onto the farm. This time of year farms will be taking in new breeding ewes or replacing stock rams.

Treatment involves dipping the incoming sheep and holding them in isolation from the rest of the flock to allow the dip to take effect. Injectable anti-parasitic agents can be used, but when it comes to specific treatment the best advice is always to contact your vet.

With sheep scab (as with many skin parasites) we take special care when dipping. With an outbreak of scab we always advise a double dip about 8-10 days apart. Follow the 4x100pc rule when dipping i.e. 100pc of the flock in each session; immerse 100pc of the sheep's body in the dip; keep the animal in the dip for 100pc of the recommended time (60 seconds) and dip at 100pc of the recommended strength of the dip mixture until the last animal has been dipped.

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Dipping has been replaced somewhat by injectable medicines recently, but remember that with medicines, the dose is subject to the weight of the animal. Ensure an accurate weight is known for the sheep as an average weight leads to an average dose which means a third are underdosed and another third are overdosed. Also, with injections it's easy to skip one animal in a race and that one infected sheep can quickly reinfect the remaining flock in no time.

With injections it's hard to know which missed and which hit; but not so if one misses the dip as it's easy to see whose fleece is not wet at the far side of the dip bath. Marking the sheep with different colours before each treatment means anyone with no colour after the first treatment can be isolated and treated individually to prevent reinfecting the rest.


  • Dip or treat all sheep on the farm against scab (or other parasite) once a year;
  • Treat all new arrivals and isolate them for two weeks before releasing them into the flock, ie breeding rams, newly bought hoggets;
  • Take best possible precautions with shearing personnel and equipment, including vehicles;
  • Never transport animals when a skin parasite is active on the farm. Treat, hold, repeat treatment two weeks later if required, and then transport.

Moving back to the general notes on scab; this is one humdinger of a disease when it gets going. The mites are mobile and rapidly reproducing. They have the ability to spread very quickly causing endless welfare and productivity problems on infected farms. Contact with neighbouring sheep spreads it and with mountain or commonage grazing, it's easy to see why it is a notifiable disease.

Goats (and cattle occasionally) can get the disease and so must be included in the control of an outbreak. This time of year, with thick, moist fleece and farm-to-farm movement, one wonders how the sheep farmers of northeastern Scotland are coping with the outbreak.

Livestock vehicles are continuously doing an up-and-over route of transport to and from Europe. This means that they travel to the north of Ireland, over to Scotland and down through England to cross the Channel to Europe. The best way to move any disease is to move the infected animal. Let's ensure no "disease smuggling" occurs as the livestock vehicles go about their business.

Closer to home we rely on the vet to formulate a Flock Health Programme, vis-a-vis medicine usage and parasite prevention. If a skin condition does not clear quickly after normal treatment, your vet will take a skin scraping for analysis of the offending disease. This saves money by focusing your medicine, avoiding repeat doses, and it stops diseases by putting control points in place. That's one bug we don't want in from Scotland, thank you.

Peadar O Scanaill is a member of Veterinary Ireland Animal Health Committee and a practising vet in Ashbourne, Co Meath. Email:

Irish Independent