IT'S high time Victorian sheep producers included an alternative drench group in rotations.

So says a senior consultant with the Mackinnon Project, Dr John Webb Ware, who believes the OP (organophosphate) drench family, in combination with other drench groups, is effective and necessary.

"It's now a fact of life that a really important tool to manage drench resistance is to make use of an OP drench," John said.

"It needs to be on sheep producers' radar."

Operating throughout southeast Australia, the Mackinnon Project consults directly with nearly 150 clients, who account for about 5 per cent of the Victorian sheep flock.

"Most sheep farms in southeast Australia face some form of drench resistance," John said.

    Estimates on the extent of resistance indicate:
  • More than 90 per cent of farms have resistance to "clear" drenches.
  • Most have resistance to "white" drenches.
  • Between 80 and 85 per cent of farms have resistance to "white and clear" combinations.
  • There is an emerging resistance to the other macrocyclic lactones in sheep drenches - ivermectin, abamectin and moxidectin.
  • Nearly 30 per cent of farms (and rising) have resistance to ivermectin.

"To ensure effective drench rotation programs, we're clearly looking for alternative drenches so we don't have to continue to rely on the ML group, which is under increasing pressure," John said.

"Some producers even use old drenches more often in an attempt to overcome their failure to control worms, which just compounds the problem."