Resistance to moxidectin in the mite which causes sheep scab has been confirmed in England and Wales, prompting SAC Consulting, part of Scotland’s Rural College (SRUC), to review its sheep scab diagnostic data.

Sheep affected by sheep scab
Credit: Prof Neil Sargison, Royal Dick School of Veterinary Studies

The notifiable disease significantly impacts on the welfare and productivity of the animals during winter, with investigation of itchy sheep results showing a peak in sheep scab during January and February (see graph).

If left untreated, the disease can cause intense irritation to the sheep, lead to reduced quality of sheepskins and wool and also affect the growth rate of lambs.

An early diagnosis is particularly relevant in the run-up to lambing, when it is easier to treat the flock prior to the birth of any lambs.

Sheep scab is caused by Psoroptes ovis mites and confirmation of infection requires microscopic examination of skin samples from affected animals.

The disease has been notifiable in Scotland since 2010, with annual notifications ranging from a high of 150 in 2011 to a low of 81 in 2014. The first three months of 2017 saw 34 notifications.

Over the last five years, SAC Consulting has examined more than 300 samples with scab mites detected in almost a third (32 per cent) of these samples and lice in 17 per cent.

George Caldow, Head of SAC Consulting Veterinary Services, said:
“The resistance the sheep scab mite has shown to moxidectin makes an accurate diagnosis essential. It will allow vets and farmers to select the correct treatment and avoid the overuse of macrocyclic lactone injections. I would encourage farmers to work with their vets to promptly investigate the cause of itchy sheep, and to take advantage of the free testing available.”

Seasonal trend of sheep scab diagnoses. Monthly diagnoses for the years 2011 to 2017:

	Related Links
	Supplementing Sows’ Milk in Situ Boosts Litter Weaning Weight
	Avian Flu Found in Wild Birds in Dorset
	CHeCS Farmers Rewarded by Defra in new TB Rules
	NOAH’s Review of 2017 – Brexit has been Key