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© Tim Scrivener The UK’s first case of resistance to a monepantel wormer is a wake-up call for sheep farmers and advisers to follow best practice guidelines, an industry expert has warned.
It has emerged the farm where the case occurred, previously saw multiple resistance to other wormers meaning it was relying heavily on the newer monepantel type. See also: Wormer resistance
in sheep explained The animals were also being moved to low-challenge pasture following treatment, which is highly selective for resistance leading to a “perfect storm” for resistance to
develop. Speaking for the Sustainable Control of Parasites in Sheep (Scops) group, Sheep consultant Lesley Stubbings said the issue revealed the dangers of failing to correctly integrate
newer wormers into control programmes. “Scops understands the farm concerned had a history of triple resistance to the 1-BZ [white], 2-LV [yellow] and 3-ML [clear] groups of anthelmintics.
“This meant they were relying almost exclusively on the newer monepantel wormer, the 4-AD [orange] group, for worm control,” Ms Stubbings said. Other sheep farmers can avoid this risk by
following Scops guidelines on the use of the 4-AD and 5-SI (purple) wormers, she added. Scops has been advising that 4-AD and 5-SI wormers should be carefully incorporated into control
programmes as a quarantine drench and a mid/late season treatment for lambs. That advice was given to avoid the exact situation where the other three groups were no longer effective and the
group 4AD was relied upon alone, Ms Stubbings added. The resistance case was reported in the _Veterinary Parasitology_ journal SCOPS ADVICE ON ORANGE AND PURPLE WORMERS The two newest wormer
groups (4-AD and 5-SI) should be alternated and incorporated into worm control programmes on all sheep farms, not left until others fail There are only two occasions when a group 4-AD or
5-SI should be used – quarantine, and mid/late season as a one-off annual drench for lambs Groups 4-AD and 5-SI should only be used at other times under veterinary direction and then only if
the full anthelmintic resistance status of the farm is known. Effectiveness of products used should be monitored carefully Ensure the correct dose rate (by weighing animals and treating to
the heaviest in a group), calibrate the gun and administer correctly, over the back of the tongue If moving to low-challenge pasture after treatment, sheep must either be left on the dirty
pasture for four to five days before moving, or at least 10% of the animals left untreated Check the efficacy of wormer treatments on a regular basis