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Home Worm Control Program – Summer rainfall / tablelands and slopes When to Drench and When to WormTest for Sheep – Summer Rainfall/ Tablelands and Slopes

When to Drench and When to WormTest for Sheep – Summer Rainfall/ Tablelands and Slopes

Why check worm burdens in sheep?

Checking worm burdens with a WormTest is essential for correct and timely drenching decisions. The result is healthy sheep without unnecessary drenching. WormTests are the best basis for drenching decisions outside of recommended times. Pale skin and eyes, bottle-jaw, weight loss, a tail in the mob, and deaths may mean that your sheep need drenching. If so, these signs occur well after production losses from worms are already occurring in the mob. WormTests give early warning of significant production losses.

How are worm burdens tested?

Checking worm burdens throughout the year using WormTests is a critical part of the WormBoss worm control program.

Most WormTests are done through a laboratory. However, worm egg counts (but usually not larval cultures) can be done by producers if they have the equipment and skills.

Which mobs and how many should have a WormTest?

WormTest at least one in every three mobs that are similar regarding drenching history, paddock type and class of sheep.

Testing representative mobs saves the cost of testing all mobs. But this assumes the mobs, their paddocks and drenching history are very similar. If in doubt, test additional mobs.

When should WormTests, drenches and Barbervax® vaccination be routinely done?

The Barbervax® program is an optional strategy to control barber’s pole worm; it will not control other worms. Routine drenching (pre-lambing for breeding ewes and weaning for lambs) and routine WormTest times will still apply, however non-routine drenching will be reduced when Barbervax® is used correctly. Protection against barber’s pole worms requires three initial ‘primer’ vaccinations at 3–4 week intervals. In the next year of use, one priming vaccination will provide protection from 5 days later. A vaccination schedule can be customised by a professional advisor.

Table 1. Routine Barbervax® vaccination times

Lambs or hoggets not previously vaccinated
  • V1: lambs at lamb marking; hoggets during October.V2: 3–4 weeks after V1.V3: 3–4 weeks after V2.V4—V6: after V3, give at 6-­weekly intervals while protection is required.
Hoggets vaccinated as lambs the previous year
  • V1: Give in November/December (earlier if spring is wet)
  • V2–V5: after V1, give at 6-weekly intervals while protection is required.
Breeding ewes not previously vaccinated (assumes a spring lambing)
  • V1: 8–9 weeks pre‐lambing.V2: 4–5 weeks pre­‐lambing.V3: 1–2 weeks pre‐lambing.V4: lamb marking.V5 onwards: after V4, give at 6‐weekly intervals while protection is required.
Breeding ewes vaccinated the previous year
  • V1: 1–2 weeks pre‐lambing, with an effective pre­‐ lambing drench (for scour worms and early barber’s pole worm) and move ewes to a low worm-­‐risk lambing paddock prepared in previous 6 months.V2: lamb marking.V3—V6: after V2, give at 6­‐weekly intervals while protection is required.
Note: V=vaccination, the number (1–6) refers to first, second (and so on) vaccination in the series given in one barber’s pole worm season.

It is also important to follow the routine drench and WormTest times shown below.

Ideally, a mob WormTest should be done 4 5 weeks after an effective (i.e. not priming doses) vaccination, from the third vaccination onwards, so that the result is known before the next vaccine muster.

Routine drenching times

In this region there are two situations where sheep should be drenched without a prior WormTest, these are:

  • Pregnant ewes just prior to lambing when they enter their lambing paddock. The worm challenge is typically about to rise at this time of year and lambing ewes, which experience a temporary loss of immunity during lactation, can contribute to a large increase in paddock contamination and a source of ongoing infection for themselves and their lambs.
  • Lambs at weaning. Weaned lambs are highly susceptible to worms, especially from the stress of weaning. Summer weaning also coincides with high worm-risk weather conditions. Drenching at weaning will help weaners to achieve the growth rates needed for survival.

In both cases, use a drench known to be effective on your property. Preferably, use a short-acting treatment, and where possible, use a multi-active combination. After these drenches, move the sheep into prepared low worm-risk paddocks.

Note: An ‘active’ is the specific chemical in a drench responsible for killing worms. Some drenches contain more than one active and are called ‘multi-active’ or ‘combination’ drenches. See Appendix 6: Drench groups and actives.

Routine WormTest times

WormTests can be done at any time; however there are certain routine times to WormTest (preferably with a larval culture):

  • Pre-shearing.
  • Pre-lamb marking for ewes. (Generally, there is no benefit from drenching lambs at lamb-marking, however, if a WormTest indicates that the ewes need drenching, the lambs should also be drenched).
  • Pre-weaning for ewes. (Not for lambs as they will be drenched at weaning).
  • From weaning time, WormTest all mobs at 4–6 week (summer) or 6–8 week (winter) intervals after they have been given a short-acting drench. If a persistent drench is given, use the Drench Decision Guide to decide when a WormTest should be done.

When are other WormTests done and drenches given?

The timing of WormTests and drenches will vary between farms and seasons. Use the Drench Decision Guide (see below) to weigh up important factors when deciding when to drench or WormTest on your property. These factors are signs of worms, time since last drench, the persistence of the last drench, WormTest results, recent rainfall, and condition of sheep and pastures.

If drenching is done for other reasons (such as an early drench before holidays or harvesting), recommence WormTests 4–6 weeks (summer) or 6–8 weeks (winter) after the drench was given. Then use the Drench Decision Guide to decide when to drench or WormTest again.

What samples should be collected for WormTests?

Sheep do not need to be yarded for a WormTest. Collect fresh dung from the paddock. Obtain WormTest kits or sample collection details from laboratories or resellers in your area. Follow the instructions provided in the kit.

  • Avoid delays in transit (when worm eggs can hatch) by collecting and posting early in the week.
  • Ensure samples are kept cool, but not refrigerated, before sending.

If you do your own worm egg counts, use the ‘bulk’ sampling method where all of the dung is collected into one container.

  • Collect 3 pellets per pile of dung from at least 20 individual piles of fresh dung.
    • In barber’s pole worm areas collect from 40 piles of dung if the mob has over 200 sheep.
    • Choose pellets of equal size so that each sheep is equally represented.
    • If dung consistency is runny, use a plastic spoon. Don’t avoid runny or soft dung.
    • Collect lamb and ewe samples separately.
  • Dung should be very thoroughly mixed together before preparing your solution for counting.
  • Count 5 chambers from the sample.

The following fact sheet is on the WormBoss website: ‘Checking a mob of sheep for worms with a WormTest.

The WormBoss Drench Decision Guide

The Drench Decision Guide is reliable and helps to simplify decisions. There is a version of the Drench Decision Guide for each WormBoss region.

The guides consider

  • whether signs of worms are present
  • the class of sheep
  • the WormTest results
  • the condition of the sheep
  • the condition of the pasture
  • the likely worm contamination of the paddock The Drench Decision Guide will recommend
  • whether to drench now
  • whether to use a persistent drench
  • when to WormTest again

Results from the Drench Decision Guide can be applied to mobs without a WormTest if other mobs (same class, and similar drenching and paddock histories) have been tested. If in doubt, WormTest the mob.

How to use the Drench Decision Guide

You can use the Drench Decision Guide at any time, whether you are contemplating drenching a mob now or in coming weeks. Not all situations require a WormTest: the Drench Decision Guide will recommend when these should be done.

Using the printable version:

  1. Firstly, refer to the Drench Decision Guide, which is provided separately.
  2. Start on the page that shows the ‘Drench Decision Guide Questions’.
  3. Read Question 1.
  4. Follow the ‘go to’ information on the right for the answer that applies to your mob.
  5. Only go to the question or recommendation to which you are directed by your answer.
  6. When you are directed to a letter, this is the final recommendation, and is shown on the next ‘Recommendations’ page.
  7. Also read the important information in the green boxes.

The Drench Decision Guide is also available as a ParaBoss web tool where it is presented differently to the paper version described above, so that you only see the questions and a recommendation relevant to your answers.

Using the web version:

  1. Agree to the terms of use and press ‘Start’
  2. Select an answer for the first question and you will automatically be taken to the next appropriate question.
  3. Select an answer for each question and you will automatically be taken to the Recommendation, where your choices and Recommended Actions will be shown, as well as other important information.

Both the printable and interactive DDG for the region are available here:

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