22 October 1999

Double doses essential with sheep scab

SHEEP producers using ivermectin products to control scab must administer two doses seven days apart, and ensure sheep are put onto clean pasture each time.

That warning comes from Shropshire-based sheep vet Chris Lewis, who is concerned about reports of producers attempting to control scab using only one dose of ivermectin.

"Giving only one dose of ivermectin will not control scab. At best, it will kill 90% of mites, leaving the rest. This means you will face a full-blown scab problem 25-50 days later, warns Dr Lewis.

"Killing only 90% of scab mites also increases resistance risks – the most susceptible mites will be killed, leaving the rest, who may be more difficult to control. Any resistance to ivermectins might potentially build resistance to moxidectin – Cydectin – and doramectin – Dectomax, which would be a disaster."

Sheep must also be moved after each treatment. "Move them back onto the same pasture and theyll rub on the same posts, re-infecting themselves with scab."

The data sheet included with all ivermectins states that it must be given as part of a two dose strategy, administered seven days apart.

"Read the data sheet before buying products, and again before using them. These instructions are approved by the Vet Medicine Directive, and must be adhered to," urges Dr Lewis.

"Treating scab properly in the first place will cost less than having to treat again and again," he adds.