Completing a drench test to identify what wormers are still working
As some farms are reporting very high stomach worm egg counts over recent weeks, Head of Sheep Knowledge Department at Teagasc, Michael Gottstein discusses the importance of completing a drench test to identify what wormers are still working on your farm.
Stomach worms are a significant and continual challenge facing growing sheep and the shepherds who look after them. Prior to the development of anthelmintics (wormers), farmers struggled to control internal parasites in sheep and intensive sheep production systems were unheard of. In the middle of the last century, the development of anthelmintics that could kill the internal parasites in sheep allowed farmers to intensify production systems and use these chemicals to keep sheep healthy and thriving.
Unfortunately some of the parasites that infect our sheep have over time developed the ability to survive the wormers that should be killing them. This ability is genetic and passed on to their offspring, so it gets worse with each generation. It is not that case of IF but rather WHEN will the parasites on your farm develop the ability to survive an anthelmintic treatment.
The speed at which the worms develop resistance to an anthelmintic depends largely on the practices adopted at farm level. On some farms, particular wormers may stay effective for 30 or 40 years. In other cases, however, they may start to break down after 10 years.
In the below video, Michael Gottstein discusses the effect of dosing on the pasture work population:
When to dose?
Over the last few weeks, we are seeing very high egg counts coming back in faecal samples taken from lambs in the BETTER Farm programme.
This is as a result of the mild and humid conditions, which favour the hatching larvae in getting onto the grass so that they are ingested by grazing lambs. Therefore, this is an opportune time for farmers to test the efficacy of the wormers they are using on their farms.
In the below video, Michael Gottstein outlines how carrying out routine dung samples from a batch of lambs will help identify whether or not the lambs need a dose:
The drench test
The most commonly used test is called a drench test. It is quite simply two faecal samples taken from a batch of lambs. The first test is taken at the time of treatment to see what the faecal egg count was at the time of treatment. The second test is taken either seven or 14 days later (depending on the product used) to see what percentage of the egg count has reduced. In order to be deemed effective, the egg count should have reduced by at least 95%.
Steps in completing a drench test:
- First gather approximately 10-15 lambs from the group to be tested, mark them and leave them in a clean pen for 1 or 2 hours to defecate.
- Collect a sample, a teaspoonful, from at least 10 separate faecal deposits and treat the lambs with the wormer to be tested at the recommended dose rate.
- Make sure to weigh the lambs and calibrate the dosing gun to ensure that the dose rate is correct.
- Then send the faecal samples to a laboratory for testing. Send the samples as soon as possible after collection, preferably the same day.
The second test
- After a set number of days, the process is repeated.
- The same marked lambs are placed in a clean pen and left for 1-2 hours to defecate.
- Samples are again collected from at least 10 different faecal deposits and submitted to a laboratory for testing.
- This second test should be 7 days after the first test if a Levamisole based (yellow) wormer was used to dose the lambs and 14 days after the first test if a Benzimidazole (white) or a Macrocyclic Lactone (clear) wormer was used to dose the lambs.
In order to determine drench efficacy, the reduction in egg count after dosing must be calculated. If there were 600 eggs per gram (epg) of faeces in the pre-dosing sample and 200 epg in the post-dosing sample, then the reduction is 600 - 200 = 400 epg and the percentage reduction is (400/600) x 100 = 67%.
To be considered fully effective, a dose should reduce the egg count by 95% or more. In many cases, this will mean reducing the egg count after treatment to 0. Therefore, in the example above the drench is not fully effective.
Further details on completing a drench test to check product efficacy are discussed by Michael Gottstein in the below video: