Testing drench effectiveness with a DrenchTest or WECRT

Faecal worm egg count reduction tests (WECRTs) allow the effectiveness of several different drenches to be evaluated at the same time across a mob of animals. They provide a producer with information about which drenches are no longer working effectively due to the worms on their farms having developed resistance.

The test uses the same principles as the ‘before and after’ DrenchCheck test. It tests multiple drenches to determine how effective each one is at killing the different types of worms present. For effective worm management, WECRTs should be conducted on each property every 5 years.

Contact a testing laboratory or an advisor for further advice before conducting a WECRT.

While producers can conduct their own WECRT, in most areas there will also be people who can do the on-farm actions of the test for you (such as testing laboratory staff, advisors, rural merchandise staff or contractors offering other cattle related services).

You will need

  • An assistant is considered essential.
  • Drenching equipment: use separate equipment for each drench, or else clean thoroughly between drench groups.
  • A small measuring container (for checking the drench dose).
  • Drench: enough for 15 animals of the maximum weight you will be drenching (this allows for some spare doses).
  • Scales for weighing the animals.
  • Dung collection bags or bottles for individual animals: 10 or 15 for every group (ask your testing laboratory whether they do 10 or 15).
  • Identification equipment: coloured tags or spray mark suitable to distinguish each group of animals for 2 weeks. If animals have individual tag numbers these should be recorded, but colour coding makes the job easier.
  • Recording equipment: pen and paper—use this link for a WECRT recording sheet and the recording sheet provided by your laboratory.
  • Other dung sampling equipment (spoon, soapy water, gloves, table/trolley, esky): see ‘WECs ’ for how to collect a faecal sample.

Any one mistake can ruin the results of a WECRT.

  • Set aside plenty of time—around half a day for both the drenching and the collecting activities, as well as time to muster the animals.
  • Set out all the equipment close by, but protected from being knocked over by animals or you and your assistant.
  • Decide who will do what jobs, how and in what order and then stick to a routine—don’t do each other’s jobs, as this causes mistakes.
  • Go slowly, especially at the start, while you develop your routine.
  • Avoid having spectators and too much chatting, as these divert your attention.
  • Drafting and re-drafting will likely be required; ensure gates are secured between each group to prevent mix-ups and wrong treatments.

1. Decide when to conduct the WECRT

  • Choose a time of year when the animals are likely to be infected with all of the worm species of interest
  • Avoid conditions (time of year and heavily contaminated paddocks) when worm burdens can increase rapidly between the start and finish of the test (as the undrenched group and groups that receive a less effective drench are more at risk).
  • Choose a day to start the test that results in the final collection day (14 days later) being when dung samples can reach the testing laboratory without weekend delays in the post.

2. Decide on the mob to be tested

  • Select a mob of cattle, preferably young (6-12 months) that have had no previous treatments.
  • If there are not enough animals of the same age and type, a WECRT can still be done by using smaller numbers, but the procedure must be modified to include individual worm egg counts both before (day 0) and after drenching to get the percentage reductions for each animal.
  • If there are not enough animals to do all the drench groups, then separate WECRTs in different seasons or years may need to be done. Your professional adviser can help with the design.

3. Conduct a preliminary WEC (‘pre-test’)

  • At the time of year when the WECRT is planned, use a routine faecal worm egg count (WEC) to decide whether the mob has enough worms to conduct the test.

4. Obtain drenches to test

  • It is useful to seek professional advice in selecting the drenches to test, especially since some drenches with lower effectiveness may be useful in a combination.
  • For a comprehensive WECRT, WormBoss recommends testing these actives (groups):
  1. a clear drench (levamisole),
  2. a white drench (benzimidazole such as fenbendazole), and
  3. a ML (macrocyclic lactone such as abamectin).
  • It is important that pour-on drenches are NOT used, as licking will spread the chemical between the groups. Use only injectable or oral formulations.

5. Select animals for testing

  • 10 to 15 animals are needed for each drench group. The total number of animals needed equals the number of drench groups x 10 or 15. In the initial draft, include extra animals in case some are deemed unsuitable during the allocation and drenching process.
  • Choose an even line of animals from the group, excluding heavy or light animals and any sick, injured or unusual animals.
  • Ideally, 15 animals are used initially for each group; however, a minimum of 10 will be sampled from each group in 14 days (ask your testing laboratory whether they want 10 or 15 samples). If only 10 are needed, the extra 5 per group are ‘spare’ in case of deaths or escapes or inability to collect dung from animals at sampling time.

6. Conduct the test

  • Allocate enough time: at least 20–30 minutes per group is needed on the ‘drenching day’ after the cattle have been yarded.
  • Decide how each group will be identified from the other, ensuring that your choice will still be clearly visible in 2 weeks—different coloured tags for each drench group are recommended and record this next to the drench treatment group.
  • Look for 5 or more of the biggest animals in the mob kept for the test and weigh these. Record the weights. If numbers are restricted and hence the lines are uneven, then weigh every animal.
  • Run the whole group to be tested into the race progressively and mark or tag the first animal so it is allocated to the first drench group, mark the second animal to the second group and so on, so that animals are allocated in turn to the different drench groups (with any spare animals left unmarked). Individual tag numbers of the animals can also be recorded.
  • Draft the animals into the separate treatment groups (set any of the spare animals aside). With more test groups, multiple drafting is likely to be required, i.e. draft off a couple of groups with the remaining ones still boxed together; when these initial groups are treated, draft off more groups until all groups have been drafted off and treated individually. Care is required to ensure all animals get their correct treatment.

7. Calculate doses of each drench being tested and check the drenching equipment

  • Using the weights of the heaviest animals in the test mob, calculate the dose of each drench to be tested (each group will be drenched to this ‘heaviest animal in the mob’ weight). Follow the manufacturer’s directions on the label of the drench container or as professionally advised. Record the dose rate (ml per animal) to be given alongside each drench treatment group on the recording sheet (different drenches may have different dose rates).
  • If using a drench gun and pack, ensure that they are thoroughly cleaned of previous drench and fill the pack with about double the volume of drench required for the first drench group. After setting the gun to the desired dose, measure a few doses into a measuring container and adjust the drench gun until it is correct and consistent.
  • If using syringes for each drench, these are already tested as accurate. Ensure recycled syringes are not cracked or leaking from the plunger. Have a container (with the drench in it) that can easily have the drench withdrawn with the syringe, rather than trying to get the syringe into the mouth of a large drench drum. A different syringe for each drench group is preferred.

8. Treat each of the drench treatment groups separately

  • Bring the first of the drench treatment groups into the race.
  • Check that the correct details have been recorded for the tag colour, individual tag number, spray mark or other information to identify this treatment group along with the treatment and dose used.
  • Collect a dung sample from the rectum of each animal for individual worm egg counts before they are drenched (day 0). These counts will be compared to the WECs conducted after drenching to get the percentage reductions for each animal.
  • Bring the first group into the race and take a dung sample from the rectum of each animal until the numbers of required samples are collected. Do not mix dung from different animals (see ‘WECs’). Place the dung in sample bags/bottles and then in another bag or box that clearly identifies them as ‘day 0, before drench’ samples and the specific treatment group. If dung can’t be found in an individual animal, it can usually be collected if an animal is set aside for 15–30 minutes. Discard any animals from which dung cannot be collected from the trial.
  • Keep the samples in a cool place or an esky during the collection process, with ice bricks in hot conditions.
  • Treat each of the animals very carefully, watching them for a few seconds to see if they spit the drench out. If any does, reject this animal from the trial (remove the coloured tag or obscure the coloured mark if one has been applied, to ensure this animal is not sampled later) and substitute with one of the spares. Treat and identify this new animal as for the rest of the group. Once treated, ensure they are properly marked and release these animals from the race.
  • Thoroughly clean the drench gun and pack between treatment groups, or for syringes, use a new one for each group. Refill with the next treatment and set up the gun according to the dose calculated earlier.
  • Repeat the above steps for each drench treatment group.

9. Return the test animals to the paddock

  • Any unused spares or rejected animals should be returned to the original mob (drench them if the remainder of the mob is being drenched at this time).
  • Mix all of the treatment groups together and graze them together for the next 14 days in a secure paddock convenient to the yards to avoid losses and so they are easily re-mustered.
  • The test mob can be boxed with other animals; however, they will need to be drafted from the other animals in 14 days, and it is usually easier to keep them alone.

10. Collect dung samples from test animals 14 days after drenching occurred

  • Allocate enough time: at least 20–30 minutes per group is needed on the ‘collecting day’ after the cattle have been yarded.
  • Yard the test animals and draft them into their separate treatment groups.
  • Assemble the bags/bottles for samples from the number of animals (10–15) as directed by your testing laboratory.
  • Bring the first group into the race and take a dung sample from the rectum of each animal until the numbers of required samples are collected. Do not mix dung from different animals (see ‘WECs’). Place them in sample bags/bottles and then in another bag or box that clearly identifies the specific treatment group. If only 10 samples are required, the other animals are spare in case dung can’t be found in an individual animal.
  • Keep the samples in a cool place or an esky during the collection process, with ice bricks in hot conditions.
  • Repeat for the next group of animals and continue until all groups of animals have been dung sampled.
  • Animals can be returned to the main mob.

11. Complete the submission form

  • Ensure that the laboratory knows that these samples are part of a WECRT, that each treatment or day 0 set of samples is identified as a group and that all groups are to have a larval culture or DNA test done separately, regardless of the worm egg count.

12. Package and send the samples

  • Pack and send the samples as per the laboratory’s instructions.

13. Receive the results

  • Final results will be available about 10 days after the samples were received by the laboratory (allowing time for the larval cultures and analysis to be completed).
  • The worm testing laboratory or veterinarian will analyse and interpret the test data.
  • Results will be provided for each drench and for each worm type present as a per cent reduction in the number of worm eggs.

14. Understand and use the results

  • A cattle drench is classed as ‘effective’ only when it reduces the worm egg count by 95% or more. At lower levels of effect, the worms on your property are drench resistant.
  • Each worm type may be resistant or susceptible (not resistant) to different drenches and at different levels. For example, ‘drench x’ may reduce the barber’s pole worm (Haemonchus placei) infection by 98% but only reduce the stomach hair worm (Trichostrongylus axei) infection by 30%. ‘Drench x’ would therefore be an effective barber’s pole worm drench, but not an effective drench against stomach hair worm.
  • Results for individual animals may vary. Using mathematical methods, the upper and lower 95% confidence intervals (CI) are calculated for each estimate of efficacy, giving the reliability of the efficacy. As an example, if a 68% reduction is calculated with 63-73% CIs, we can be confident of the 68% result for the mob. However, if the CIs are 22-90%, the likelihood of 68% efficacy being true for the mob is rather low.
  • Drenches with less than 95% efficacy can still be useful when used in combinations.
  • If only a limited number of drenches were tested, and none or few were 95% effective, more will need to be tested to find those effective on your property.
  • Seek professional advice to interpret WECRT results and to decide suitable drenches for future use.