Sheep farmers advised to carry out drench testing
Drench tests carried out as part of the Sheep Technology Adoption Programme (STAP) between 2013 and 2015 indicated that up to half of the drenches used were ineffective against the gut roundworms that cause the main mid-season problems, .
Therefore, if you use one of the benzimidazole, levamisole, or macrocyclic lactone broad spectrum wormers against gut roundworms, it is important to do a drench test to check that it is working, advised Teagasc experts writing in the current edition of the
Todays Farm magazine.
Grazing sheep are naturally exposed to parasitic roundworms that live in the gut, and can cause chronic dis- ease, ill-thrift and occasionally death in flocks.
Worm control depends on effective worming products and grazing management.
However, development of drug resistant worms is an unavoidable result of continuous use of wormers.
Drug resistant worms can survive a dose of wormer that would normally kill them, and will lead to one of the biggest challenges facing sheep farmers, if left unchecked.
Treating lambs with products that do not give the desired control is a waste of time and money.
It results in poor flock performance, because the sheep end up carrying a heavy worm burden, despite having been treated.
One of the options in the STAP was to test the efficacy of the anthelmintic treatment.
This was done by means of a drench test, which is a modification of the faecal egg count test.
Individual faecal samples were collected from a group of lambs before and after anthelmintic treatment.
The number of worm eggs present before and after was subsequently determined in the lab. An impressive number of drench tests (4,211) were taken by farmers during the three years of the STAP programme.
Information on the anthelmintic product used was available for 3,771 of these tests.
Drench failure was observed in STAP farmers’ flocks, at 13% to 65% for the different drench active ingredients.
These figures are in line with a drench test study carried out on a small number of Teagasc clients’ flocks in 2012.
Drench failure does not necessarily mean that the worms are resistant. Drench failure could be due to a myriad of other reasons relating to sub-optimal treatment, such as use of a faulty dosing gun, or administration of the incorrect dose rate.
More than a quarter of STAP participants (who complied with the drench test instructions) found out the pre-treatment faecal egg counts were below 200 eggs per gramme. In sheep, this indicates a low level of gut parasitism, so many farmers were treating unnecessarily.
This result highlights the merit of using worm egg counts for correct timing of treatment.
If you use a benzimidazole, levamisole, or macrocyclic lactone broad spectrum wormer, the simplest check, and a good post-treatment practice, is a drench check to determine if any worms survive after drenching.
This involves getting faecal samples after treatment (between five and 16 days after, it depends on the product used) and sending them to the lab for a faecal egg count.
If eggs are present, more detailed investigation is warranted, requiring taking samples both before and after wormer treatment.
Samples would be needed from at least 10 lambs not treated in at least six weeks (longer if treated with a long-acting wormer).
Drench tests offer an impartial and cost effective method to test the efficacy of wormers.
Until 2009, farmers had only benzimidazole, levamisole, and macrocyclic lactones wormers available.
Then, two new “families” of wormers were launched on the Irish market, the first in 25 years. These two new “families” of wormers are prescription-only medicines, and if used judiciously, they afford new opportunities for Irish flock owners to prolong the lifespan of the older wormer “families”.
