Sheep Scab: Protecting Flock Health

Sheep scab is caused by a mite (Psoroptes ovis) and is a highly contagious disease which can have a significant impact on your flock’s health, productivity and welfare.  

The mite lives on the surface of the skin and once on a sheep its mouthparts abrade the skin surface which then provides further food for the varying life stages of the mite which all happen on a sheep. One full life cycle takes between 10 and 19 days. Adult females can live for up to six weeks and lay two to three eggs daily. Once established the mite population doubles every six days. The clinical signs are a result of an allergic reaction to the faeces passed by the mites.  

Clinical signs can be seen from 10 days post infection but can be four to six weeks before disease becomes apparent.  

The speed of disease development depends on various factors including: 

• Location of initial infestation 
• Fleece density and depth 
• Environmental conditions 

It is also important to note that some sheep are carriers of sheep scab mites without showing clinical signs themselves. This includes sheep that have recovered or been re-infected. They will have low numbers of mites but remain infectious to other sheep. 

Clinical signs

Early stages:  

• Can appear clinically normal 
• Restless and rubbing with stained areas of wool or tags of fleece seen 

Later stages: 

• Rubbing against fences/post; biting at flanks; scratching with hind legs and or horns 
• Dry crusty yellowish scabs in fleece with a moist red outer ring 
• Wool loss with wounds or abscesses also seen in some cases 
• Loss of body condition 
• Increasing number of mites and these may be visible at the edge of lesions 

Impact

Welfare is significantly impacted by infestation and there is also a health and productivity impact. It has previously been estimated that he cost to the UK sheep industry £78 million to £202 million a year.

Costs to consider:  

• Preventative or treatment products and associated delays to slaughter due to meat withdrawals 
• Condemnation at slaughter 
• Increased feed costs to compensate for body condition loss 
• In young lambs can result in severe debilitation leading to death in some cases 
• If ewes are affected when in lamb, they may have lower birthweight lambs and or higher early lamb deaths 

Infection

The main source is other sheep – consider: 

• Bought in animals 
• Returning animals e.g. from common grazing or shows 
• Animals missed at gather 
• Neighbours 

Infected fences/equipment as the mites can survive and be infective for up to 17 days off the sheep. Consider: 

• Fence posts, trees or bushes that have been rubbed on 
• Handling facilities 
• Trailers/floats 
• Shearing equipment  
• Contaminated clothing 

Diagnosis

Sheep infected with lice or other external parasites can show similar clinical signs therefore it is important to confirm which ectoparasites are present.  

There are two methods to diagnose sheep scab: 

1. Skin scrapes and a wool plucks from the edge of lesions can be examined under the microscope to look for scab mites or lice. 
2. Blood samples to look for antibodies which can be detected from two to four weeks post infection. Antibodies can persist for three to nine months post successful treatment, with the levels dropping within four weeks. Twelve animals per management group should be sampled (or all of them if less than 12).   

Use 

1. When disease is suspected but mites are not being found 
2. To look for animals that are infected that are not showing clinical signs 
3. In quarantine for new or returning animals 
4. To differentiate from other causes  

Sheep scab is one of the animal health and welfare interventions of the Scottish Government’s preparation for sustainable farming funds. Within this scheme you can claim for an investigation to determine your flock’s status using the blood test mentioned above.  

Reduce the risk 

• Ideally maintain a closed flock 
• Good boundary fencing (at least 1m apart)  
• Quarantine of returning or new animals 
• Investigate cases of itching or wool loss in your sheep.  
• Be vigilant with people or equipment that will be in contact with your sheep 

Have a plan in place that assesses and reduces the risks.  

Treatment

If sheep scab is diagnosed, you need to treat all the animals in the affected group or flock.  

Organophosphate plunge dipping: 

1. Kills scab mites within 24 hours and reduces the clinical signs and used correctly protects against reinfestation for up to eight weeks. 
2. Also effective against other external parasites such as ticks, lice and blowflies. 
3. Sheep must be in dip for at least 60 seconds with head submerged at least twice.  
4. OPs are toxic, consider health and safety of operators and environmental implications. 
5. Requires a certificate of competence to buy/use and a licence to dispose of.  

Injectable clear wormers – please seek veterinary advice as the dose regime and post treatment instructions vary. If using these products be aware that: 

• Sheep may continue to scratch/rub for up to 10 days post treatment.  
• Handling pens and fields will remain sources of infection for up to 17 days. 
• Treated sheep may remain infective for up to 12 days. 
• The use of these products will increase the risk of developing resistance in the gastro-intestinal parasites.  

If sheep still appear to be itchy post treatment (> 10 days if injectables used) please consider the possible factors below and consult your vet.  

1. Was treatment done correctly?  
2. Was scab diagnosed or could it be a different cause? 
3. Could the sheep have become re-infected? 

Resistance to the injectable products has been reported but it is important to rule out other reasons. 

As a reminder as part of the Animal Health and Welfare Interventions funded through Preparing for Sustainable Farming (PSF), there is funding available for flock screening for sheep scab, to help determine sheep scab status of your whole flock. This is the last year which PSF funding will be available to farmers. You must complete your investigations and actions for the year by 31 December 2025. Claims must be submitted by 28 February 2026.  

Useful links: 

• Sheep Scab Moredun

• Preparing for Sustainable Farming guidance

• Sheep scab: how to spot and report the disease

• Sheep dipping code of practice

• Sheep dipping: Advice for farmers and others involved in dipping sheep

Kythe Mackenzie, Veterinary Investigation Officer, Kythe.Mackenzie@sruc.ac.uk

Unearthed is the exclusive SAC Consulting members' monthly newsletter. Unearthed offers insights and tips from our experts on what we think is in store for farming and crofting in the coming months in order to protect and enhance your business.

Posted by Unearthed News on 15/09/2025