Testing Drench Effectiveness with a DrenchTest or 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.

• 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.

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.

• 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):
• a clear drench (levamisole),
• a white drench (benzimidazole such as fenbendazole), and
• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

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.

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

• 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.