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 too daunting a project if a few basic rules are followed.
The youngest sheep on the property should be used and a bulk worm egg count done first to ensure that there are a minimum of 300 worm eggs per gram of dung (epg) present.
You then set up groups of 15 sheep, using colour raddles so that they can be identified again easily. One group is left undrenched, the Control group. One group is drenched with a benzimidazole (BZ) white drench, one with a levamisole (LEV) clear drench and 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 for example that there is moderate to severe worm drench resistance to a group of drenches, say the BZ drenches on your property, then there is no point in repeating testing on that type of drench.
After 10-12 days, samples are then collected directly from the animals, rather than from the ground, to avoid contamination with the hundreds of microscopic worm eggs already lying there, which would give an inaccurate result. Ten samples are collected from each group of 15 sheep ... allowing for the possibility that the rectums of some sheep may be empty!
After sample collection is complete the sheep in the control and half dose ivermectin groups should then be 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.