Mid, North-Eastern Victoria and Southern NSW are facing ever increasing problems with sheep worm drench resistance.
Faecal Egg Count Reduction Test (FECRT) or Check-Resistance Trial
Farmers wishing to discover their drench resistance status usually set up a Faecal Egg Count Reduction Test (FECRT) or Check-Resistance Trial. This is not a difficult test to conduct, following the guidelines below:
The youngest sheep on the property should be used. A bulk worm egg count should be performed prior to drenching to ensure that there are a minimum of 300 worm eggs per gram of faeces (epg) present.
You should then set up groups of 15 sheep, using colour raddles so that they can be identified again easily. The groups are treated as follows:
- One group should be left undrenched (the Control group).
- One group is drenched with a benzimidazole (BZ) white drench
- One with a levamisole (LEV) clear drench
- One group is given a mixture of BZ and LEV, a combination drench
- It is also important to give one group of sheep a half dose of ivermectin, a type of macrocyclic lactone (ML) drench
- Other groups can be given any other combinations or drenches that you wish to test such as napthalophos with BZ or napthalophos with LEV.
If you already know that there's a moderate-to-severe resistance to a group of drenches, for example BZ drenches, on your property, then there's no point in repeating testing on that type of drench.
After 10-12 days, collect samples directly from the animals, not from the ground. This is to avoid contamination with the countless microscopic worm eggs still present on top of the soil. Ten samples should be collected from each group of 15 sheep - this allows for the possibility that not all sheep will produce samples at the time of collection.
After sample collection is complete, the sheep in the control, and half-dose ivermectin groups should then be fully drenched.
On receiving the samples in the laboratory we do individual worm egg counts on all samples and then can calculate the efficiency of each type of drench.
It's a good business decision to know the drench resistance status of your property. This knowledge makes choosing the right type of drench, and planning drench usage for the next three years easy, and reduces the air of complexity which so often unnecessarily surrounds this process at present.
Also, it is easy to check the efficacy of one particular drench by sending us ten samples collected directly from the sheep 10-12 days after drenching. This is called a Check-Drench test.
We strongly suggest that all newly purchased sheep are always quarantine drenched, off the truck, with drenches from at least 3 broad-spectrum groups. This will help to avoid importing drench resistant and Barber's Pole worms on to your paddocks.
It's a good insurance policy in these times of rapidly escalating drench resistance.