Farmers should assume any incoming sheep are carrying scab mites to curb its spread after a survey of Northern Ireland sheep producers¹ revealed sheep movements to be the leading cause of infestation.

Published in August, the survey found widespread cases of scab among flocks, with 36% of farmers indicating they had at least one outbreak of sheep scab in their flock within the previous five years and 39% believing scab was introduced to their flock via a purchased animal. Some farmers also reported their most recent outbreak had cost them over £2500, although costs were variable.  

Researcher and vet Paul Crawford said the results highlighted knowledge gaps that needed to be addressed to improve sheep scab control. 

"The survey shows there are knowledge gaps concerning parasite biology, disease transmission, prevention and treatment options, as well as a lack of awareness of some relevant industry guidelines.

For example, some farmers rely on clinical signs alone to rule out the possibility that newly purchased sheep are infested with sheep scab before mixing them with their flock. This activity poses a high risk for introducing sheep scab into previously uninfected flocks. 

The inadequacy of some farmers' quarantine rules, or their inability to follow them, was also reported by farmers as being the cause of their flock infestation," he added. 

Quarantine Procedures for Scab Control 

Adopting strict quarantine procedures for any incoming sheep and understanding the entire contamination route are vital to curb its spread.

Mr Crawford explained: "The sheep scab mite can live off sheep for 16- 17 days, so quarantine isn't just as simple as putting sheep in a separate field; it is about understanding the entire contamination route. This includes everything sheep come into contact with from the trailer through to fences in the yard," he said. 

When in quarantine, Mr Crawford recommended that animals remain there for 3-4 weeks and two weeks after arrival (no earlier), blood testing 12 animals from each group using the blood ELISA test. This would indicate whether the group of sheep had been exposed to scab and whether treatment was necessary. The test costs about £84 for 12 animals, excluding vet fees and P&P.  

When animals need treatment, the correct product must be used and the instructions must be followed, with Mr Crawford expressing his disappointment at how many poor treatments were reported in the survey.

"It highlights that there's still work to be done to remove any misunderstanding around treatments and to keep reinforcing the Sustainable Control of Parasites in Sheep (SCOPS) guidelines."

Treatment Options 

The SCOPS recommended treatment choice for scab includes:

• Plunge dipping using an organophosphate (OP) dip. 
• Using an injectable group 3-ML such as CYDECTIN 2% LA. This treats scab infestations and prevent re-infestations for 60 days from a single injection. 

Treatment choice comes down to the most practical option for that farmer and ensuring the product is administered correctly according to its guidelines. 

"The main thing when treating for scab is that you do it properly, whether using an injectable or a dip, "he stressed. 

SCOPS has worked with Zoetis, the makers of CYDECTIN 2% LA, to produce a Code of Practice for using injectables, which can be found on the SCOPS website  https://www.scops.org.uk/workspace/pdfs/best-practice-use-of-injectable-scab-treatments.pdf  

Vet Ally Ward from Zoetis added: "The results highlight that many treatments are being misused, which hinders the control of scab and can also increase resistance to the product. 

For example, some injectables, such as doramectin or ivermectin, do not have any licensed persistency. This means sheep can pick up scab mites immediately after treatment. So, if one of these is used, the treated sheep should be put into a 'clean' field and not returned to the same field they have just come out of. It is also essential to treat all sheep in a flock/mob on the same day.

Other products, such as CYDECTIN 2% LA, offer 60 days protection, so clean pasture is not required. However, it is important treatments are only used when necessary and as part of a whole farm health plan constructed with your vet or animal health advisor," she said. 

More Information

A £220,00 project is now underway in Northern Ireland to help tackle the disease. The money is being used to fund farmer meetings, vet meeting, on farm visits and data collection. For more information email info@animalhealthni.com.