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Western Australia worms, flies and lice update - February 2015

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, DAFWA (

February should be the dullest month of the year for sheep parasite control. Weaners and hoggets should have had drenches sometime in the last 2 months, and adult sheep should not need a routine drench until next month or early April. Blowflies should be off the radar at present, and lice are only on it if shearing is in progress and a decision is needed on whether to treat or not, or which chemical.

The main potential fly in the ointment is if summer drenches were not fully effective—as outlined in the last month’s ParaBoss newsletter, if given with a drench to which there was a fair degree of resistance, the sheep will keep excreting worm eggs onto the pasture. This doesn’t matter when conditions are hot and dry, as the eggs will usually be dead within a day. However, once green pasture starts to grow by mid-late autumn (we hope), the worm eggs will develop to worm larvae, which sheep pick up as they graze, thus continuing the worm life cycle. As the winter worm cycle is now started mostly by resistant worms that have survived summer drenches, the overall level of drench resistance in the worm population of the property increases, compared to the case if fewer resistant worms were allowed to survive.

So, as recommended last month: if you are not sure that summer drenches have done the trick, check the worm egg counts of a mob or two.

Barber's Pole worm: we’ve seen some high counts come back in the last month, sometimes where young sheep didn’t get a scheduled summer drench, sometimes in ewes (harder to explain). If you are in a Barber's Pole-risk zone and there is any suspicion, worm egg counts will again sort this out.

Next month: chapter and verse about autumn drenching for adult sheep.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Faecal Worm Egg Counts—Why and When.

Worm Egg Counts are a very useful tool. WECs conducted at strategic times will be helpful for a number of reasons, as they

  1. prevent unnecessary drenching saving both time and money,
  2. reduce the development of drench resistance,
  3. reduce the worm burden on the pasture,
  4. increase productivity by recognising sub-clinical disease,
  5. reduce the risk of a worm outbreak resulting in sheep losses, and
  6. give an indication of the effectiveness of a drench.

The WEC is a simple test. It involves the producer collecting 10–20 individual faecal samples from a mob of sheep. From these samples we can determine a mob WEC average. Based on the time of year, class of sheep, weather conditions, and condition of the sheep, a decision to drench or not is made.

WECs should be conducted at the following times:

  1. pre-lambing
  2. pre-marking (ewes)
  3. pre-weaning
  4. pre-first summer drench. Weaners and hoggets should be drenched at the start of summer. Older sheep should be monitored to see if this is required.
  5. Autumn before the break of the season. If a drench is required, this will reduce contamination of winter pastures. Lambing ewes that did not receive a summer drench should be drenched by early April.
  6. Any time that sheep are scouring or not performing as well as expected.
For February 2015 state outlooks, please follow the links below:
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