Once-a-year, mid-season use of a wormer from the group four or five categories (orange or purple) within a month of weaning can help boost lamb growth rates above the seasonal norm, according to independent sheep adviser Lesley Stubbings OBE.
"Exploiting the full efficacy of these two newest wormer classes, killing worms that have survived previous doses of other wormer groups, will undo selection for resistance from earlier in the season," she explains.
To encourage uptake of this concept, it has been labelled a Knockout Drench by Zoetis.
Company vet Dave Armstrong says this involves substituting just one necessary mid-season lamb treatment with a high efficacy group four or five wormer to eliminate resistant worms that may have survived previous treatments and accumulated in the lambs.
"From that point on, this can help achieve higher growth rates and quicker finish," he explains.
"For optimum financial impact, this treatment is best not left too late in the grazing season."
Of two wormers available in the UK suitable for use as a Knockout Drench, Dr Armstrong points out that one is a dual active formulation.
"STARTECT® contains wormers from two different chemical groups, specifically a group five SI and group three ML. Against the same worm species, each offers a different mode of action, with similar duration, working additively with each other.
"Essentially, the dual-active principle is that if resistant worms survive one active ingredient, most or all of them will be killed by the other.
"This makes higher efficacy possible than can be achieved by single active alone, increasing its effect against resistant worms."
In addition to this and an immediate gain from higher growth rates, Dave Armstrong says there may also be a possible longer term advantage.
"Modelling studies indicate that development of resistance to group one, two or three wormers – BZs, LVs and MLs respectively – may be delayed by strategic use of dual actives in this knockout protocol," he says.
