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Western Australia worm, flies and lice update - May 2014

New contributor! Ray Batey has joined the WA contributors—he will bring valuable insights on a wide area of that State.

Perth region and Central Wheatbelt: Ray Batey, Sheepvet Australia (ray@sheepvet.com.au)

Managing the risk of paddocks for sheep worms

Each year, from mid autumn to early winter, I am asked to investigate incidents involving sheep deaths resulting from a sudden intake of worm larvae, many farmers believing ‘it couldn’t possibly be worms’.

Moderate ground temperatures and moisture provide ideal conditions for worm larvae to develop and survive, with the potential of rapidly increasing levels of contamination. Importantly, at this time of year, when heavily contaminated paddocks are spelled, larvae continue to develop and survive without being removed by grazing, and thus they may be even more hazardous when stock are reintroduced.

A few days ago, a local farmer lost almost 25% of a small mob of Dorper hoggets over a 3-day period from acute haemonchosis (barber’s pole worm infestation) after he moved them into a contaminated paddock that had been locked up since early autumn. Winter worms may not produce the same catastrophic events, but substantial losses also occur, often at a later time when the link to the paddock is less obvious.

A simple but effective way to manage this risk is to categorize paddocks at this time of year as safe, moderate risk, or high risk in terms of potential contamination, and use this to determine:

  • which stock to put into each paddock, and/or
  • the extent of monitoring or targeted treatments that may be required.

Implementing such a strategy requires knowledge of grazing history and the status of sheep grazing the paddocks since the previous spring. This is a practical way to apply the results of egg count monitoring.

Esperance: Nicole Swan, Swan’s Veterinary Services (nicole@swansvet.com)

We have finally had rain, and seeding is in progress. The rain has been followed by some beautiful sunny 20–25°C days—perfect for barber’s pole, so we will be watching out for that in the next few weeks.
We have not done many counts in the last few weeks. Most have been low, though in barber’s pole areas I have recommended that ewes receive a Closantal drench pre-lambing.
There was only one mob with a count over 100 epg; these sheep will be drenched with a broad-spectrum drench.

Albany: Brown Besier, DAFWA (brown.besier@agric.wa.gov.au)

The worm year has well and truly started across WA. After good rains over most of the state, and with mild to cool temperatures, worm egg development will be close to its maximum. From now until pasture dry-off at the end of the year, there are likely to be worm larvae on any pastures used by sheep.

This means it is important to establish what worms are doing at the moment, as it is getting late in the year to set up the basis of good worm control.

Young sheep (2012 and 2013-drop):

Worm burdens should still be low at present if summer drenches were effective. There needs to be a few weeks of green pasture growth before any surviving worms lead to significant numbers, so it is usually well into June before we see significant worm egg counts. A check of worm egg counts is recommended sometime over the next month, but as soon as possible if it is not ‘certain’ that the summer drench was completely effective.

Ewes—adult sheep

Ewes coming up to lambing (May or early June) should receive a pre-lamb drench if counts are over about 100 eggs per gram, and a maximum of 200. They won’t need a drench if they were given an autumn drench as recommended, but if last drenched in summer or earlier, a check of worm egg counts is needed before lambing starts. A drench should be avoided if a summer drench was given, as it adds a lot of pressure for drench resistance, and there is no way of knowing whether counts are very low or surprisingly high, unless a count is done.

These recommendations apply mainly to the medium to higher rainfall parts of the state. In the cereal zones, sheep of all ages often have very low counts at this time of year—especially ewes. Worm egg counts will establish the usual annual pattern and indicate whether routine treatments are justified, or the worm risk is low except after unusually early starts to the season.

In known barber’s pole worm areas, a check of worm egg counts now is especially important, as the combination of pasture growth and relatively mild temperatures will keep this worm in contention until cold weather arrives.