Before choosing to use a long-acting drench this information is critical as these products are a high risk for magnifying any current resistance present on your farm.
Although we use animals for the test – lambs or calves – it is the adult parasites in their gut that we are actually testing. If the drench is effective then it will remove all the worm species that were present at the beginning.
If it is ineffective then the parasite will still be present and laying eggs when the second samples are collected 10-14 days later.
This test, also known as a faecal egg reduction test, counts these eggs and then hatches them to determine what worm species they have come from.
To do this the animals need to have a significant adult worm burden at the time of testing – a faecal egg count (FEC) of 700 in lambs and 250 in calves are used as indicative minimum worm burdens.
Normally 15 animals are used for each drench being tested so you need a minimum of 60 lambs or 45 calves.
A cut off point of removing 95% of the worms is used although in reality any worms left indicates some degree of drench inefficacy.
A worm management programme cannot be created without this information – for example, is the moxidectin drench you are using to give longer protection against barbers pole worm also removing the Trichostrongylus worms? Does the dual combination drench work? If not then your worm management plan is flawed.
The interpretation of the test is part science and part experience. The farmer wants to know how to use the information to make good decisions.
To do this we visit the farmer after the test results have been sent to them to discuss what it means and what actions to take.
This is also a good opportunity to discuss grazing management to manage the parasite burden on the farm. The drench will only remove the worms in the animals – 95% of the worm population are in the dung piles, on the grass, or in the top soil.
The test should be done every four to five years unless you make any major changes to the farming system.
The cost of the test is about $1000-$1500.
It is recommended that farmers do a drench check every year. Faecal samples should be taken 10-14 days after drenching to make sure that the drenching operation has been successful.
Top gun
Best practice at drenching time includes:
- Ensure the drench gun is working and delivering the correct dose
- Make certain that all the drench is swallowed
- Use an effective combination drench, and
- Drench to the weight of the heaviest animal.
• Andrew Dowling is a PGG Wrightson technical expert animal health.
