WA WormBoss Worm Control Programs
WA WormBoss Drench Decision Guides
Autumn is a make-or-break season for sheep worm control. It’s important that all sheep on the farm have low worm egg counts, or significant worm problems in winter can occur, with a flow-on into spring. As conditions become cooler and moisture levels increase, the rate of worm egg development will increase, and even moderate worm egg counts may lead to heavy worm burdens downstream.
The effects of earlier rainfall:
In some locations, heavy rains in summer will make this a wormier year than normal. The risk depends on the length of time that green pasture is present, and whether sheep were putting out many worm eggs at the time.
The longer that the pasture has remained green, the better the conditions for worm development. If germination was sporadic and mostly gone within 2 weeks, there will be little increase in the worm risk.
However, if there was a good mat of green pasture for 3-4 weeks, enough worms could cycle to increase worm burdens in sheep, even if the pasture has largely died back. Where substantial areas of green have developed, such as along creek lines, there will be an on-going source of worm larvae to infect sheep. Perennial pastures are an especially likely worm risk.
The big unknown in most cases is how many worm eggs were being deposited by the sheep in a particular paddock. If sheep received a summer drench (before the rains) with a fully-effective product, chances are that they were not putting out many worm eggs at the time, and there is unlikely to be an increase to the worm risk.
However, if no summer drench was given, or the type used was not completely effective, the continued depositing of worm eggs may be enough to fuel a significant worm cycle.
Action in weaners
A check of worm egg counts is needed now, unless this was done within the last month. If counts are over 100 eggs per gram on average, a re-drench is recommended. This is a very low trigger figure, but research shows that in young sheep, it can lead to worm problems in winter.
Action in adult sheep
Normally, we recommend a drench to ewes in late March or early April, but this year may warrant an earlier drench, as suggested in the February newsletter. Hence, this should now be given, or a worm egg count taken.
As for the lambs, use a count of 100 eggs per gram as the maximum before a treatment. Many mobs will have this level, unless they are in especially good body condition, and the majority of mobs will require a drench. This may be different in drier districts, or where there was no significant summer rain, and here a worm egg count is well worthwhile.
Barber's Pole worm
Where the pasture has stayed green through summer, especially with a boost from unusually heavy rainfall, the barber’s pole worm risk will be greater than in normal years. However, it’s not possible to predict when or whether an outbreak is likely in any one mob, and worm egg counts are the only way to check. Where counts are very high, treatment with the long-acting drench closantel may be a wise precaution, as while warm weather continues, large barber’s pole worm burdens can develop rapidly.
Recently we experienced some hot days that slowed the growth of the perennial pastures. However intermittent rain has kept them green. April 1st is our usual cut off for drench treatments but given the current conditions it can be brought forward. Now is a good time to worm test sheep to see if they need to be drenched.
Recent worm tests have given mixed results.
Despite the rain and warm weather there has been little evidence of problems with barber’s pole. It will be important to remain vigilant to monitor for signs of barbers pole-sheep lagging behind the mob, pale gums and/or bottle jaw (swelling under the jaw due to protein loss).