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Online learning: Tasmania—Deciding when to drench and what drench to use

This strategy describes when to use strategic drenches and how to decide when tactical/therapeutic drenches are needed.

Structured reading

For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the dot point provides a summary of the page.

Tip: Keep this page open and open the links in new tabs.

Tasmania: When to test and when to drench
The times for routine worm testing and drenching in this region. Not all testing or drenching is routine; other times to do these are recommended by the Drench Decision Guide, according to details you provide about your mob of sheep.

Tasmania: Drench Decision Guide
This tool recommends whether a mob should be drenched, the length of protection warranted and when to worm test again. It is your day-to-day tool on drenching decisions that should be used in conjunction with the annual program of routine testing and drenching times.

The DDG tool steers you through a series of questions about your sheep; choose the answer that applies to your mob (or make up your own scenario).

Question and answer

For those who prefer a problem based approach to learning, answer the following questions.
Each of the questions below links further down the page to the answers.

Questions:

  1. What is the purpose of a strategic drench?
  2. Which classes of sheep receive a routine (strategic) drench, and when?
  3. When is a long-acting treatment justified in winter weaners?
  4. The online Drench Decision Guide (DDG) for Tasmania assists you to decide whether a mob of sheep should be drenched now and when to test again. Open the DDG and answer the questions it offers based on the scenario (from below) that you are using. Try at least three of the following scenarios.
  • Weaners in May that received a combo drench into a prepared winter weaner paddock about a month ago, less than 5% are scouring, an egg count shows 80 epg.
  • Weaners in late January that were drenched with Monepantel at weaning in early December. There are no signs of scouring and they look healthy.
  • Ewes in November. No drench was required before lambing. About 15% are scouring.
  • Ewes received a first summer BZ/LEV/ML drench in early December, it is now mid January. Summer has been unusually wet. Sheep are not scouring but a couple of ewes were found dead in the paddock and others are lagging during mustering.
  • Late-lambing ewes in good condition just prior to being moved to their lambing paddock. A worm egg count shows 350 epg.
  • Lambs just about to be weaned, they look well-grown with no obvious signs of worms.

Answers:

You can also click on each question below to go to WormBoss pages with related information.

1. What is the purpose of a strategic drench?

Strategic drench: a drench given at a critical time to sheep that are susceptible to worm infection (e.g. weaners and pre-lambing ewes) and also given at times to reduce worm larval contamination of a pasture grazed by the drenched sheep over the following weeks or months. The sheep themselves may have had a low worm egg count at the time of this pre-emptive treatment.

2. Which classes of sheep receive a routine (strategic) drench, and when?

Routine drench times in the high rainfall region of Tasmania

  • Pre-lambing: all ewes should be treated with a short-acting drench. In wet, high worm-challenge seasons consider a long-acting product.
  • Weaning: lambs being weaned should be treated with a short-acting drench.
  • Weaners going onto fodder crops that have been prepared as low worm-risk, e.g. vegetable and cereal crop residues in later autumn: use a short-acting drench.
  • Weaners going onto highly contaminated short-rotation ryegrass: these lambs may require a long-acting product such as a benzimidazole capsule (this has a short withholding period and is generally effective against Trichostrongylus vitrinus, which is common on irrigated pastures).

Routine drench times in the medium and low rainfall and summer rainfall regions of Tasmania

  • Pre-lambing: all ewes should be treated with a short-acting drench. In very high worm-challenge seasons consider a long-acting product; this will be indicated if more drenches than usual were required prior to this time and paddocks are highly contaminated.
  • Marking: ewes in drier areas (less than 500 mm) may receive the first summer drench at marking. In high worm-challenge years ewes and lambs showing signs of parasitism may need a therapeutic drench.
  • Weaning: lambs being weaned should be treated with a short-acting drench.
  • Ewes that did not get the first summer drench at marking should be treated with a short-acting drench if they will remain on perennial pastures after weaning.
  • Weaners going onto fodder crops that have been prepared as low worm-risk, e.g. vegetable and cereal crop residues in later autumn: use a short-acting drench.
  • Weaners going onto highly contaminated short-rotation ryegrass: these lambs may require a long-acting product such as a benzimidazole capsule (which has a short withholding period and appears to be effective against Trichostrongylus vitrinus, common on irrigated pastures).

3. When is a long-acting treatment justified in winter weaners?

Only in very high worm-challenge years may a long-acting product be required in early winter for weaners. This will be indicated if more drenches than usual were required prior to this time and autumn/winter weaner paddocks could not be kept low worm-risk

4. The online Drench Decision Guide (DDG) for Tasmania assists you to decide whether a mob of sheep should be drenched now and when to test again. Open the DDG and answer the questions it offers based on the scenario (from below) that you are using. Try at least three of the following scenarios.

  • Weaners in May that received a combo drench into a prepared winter weaner paddock about a month ago, less than 5% are scouring, an egg count shows 80 epg.
  • Weaners in late January that were drenched with Monepantel at weaning in early December. There are no signs of scouring and they look healthy.
  • Ewes in November. No drench was required before lambing. About 15% are scouring.
  • Ewes received a first summer BZ/LEV/ML drench in early December, it is now mid January. Summer has been unusually wet. Sheep are not scouring but a couple of ewes were found dead in the paddock and others are lagging during mustering.
  • Late-lambing ewes in good condition just prior to being moved to their lambing paddock. A worm egg count shows 350 epg.
  • Lambs just about to be weaned, they look well-grown with no obvious signs of worms.

 


Links to the learning topics for Tasmania

  1. Introduction
  2. Grazing management
  3. Breeding for worm resistance
  4. Worm testing
  5. Drenching (you are currently on this page)
  6. Drench resistance management
  7. Sheep worms