Farmers now recognise that anthelmintic resistance (AR) is one of the biggest challenges to the future health and profitability of the sheep industry.

Task three of the Sheep Technology Adoption Programme (STAP) aims to help farmers come to terms with the problem of AR at farm level.

The summer months are the ideal time for spread of worms and, therefore, the ideal time to take faecal egg samples. Whether participating in STAP or not, faecal egg counts (FEC) are very useful in preparing a dosing programme on every farm.

Last year, over 1,300 Teagasc clients participating in STAP carried out FECs as one of their tasks.

Early indications are that it has been widely chosen again in 2014. FECs are useful in developing a strategic approach to dealing with AR.

It is important that farmers adopt the correct approach when taking these samples. It is equally important to understand how to interpret the results received back from the laboratories.

Why bother?

The objective of task three of STAP is to carry out a faecal test to establish if there is a level of parasite resistance to the commonly used anthelmintics (i.e. White drench, Benzimidazole (1-Bz); Yellow drench, Levamisole (2-LV); and clear drench / injection, Macro cyclic Lactone (3-ML) (including Ivermectin)).

This test must be carried out between 1 June and 19 September 2014, in accordance with the terms and conditions of STAP. It involves:

  • Taking a faecal sample sometime after 1 June and having an FEC carried out by an approved laboratory.
  • Dosing with an anthelmintic from one of the three groups described above immediately after taking the sample.
  • Repeating the FEC either seven days post-dosing if a Levamisole (2-LV) was used or 14 days post-treatment if Benzimidazole (1-Bz) or Macrocyclic Lactone (3-ML) products were used.

    • This test gauges the efficacy of the anthelmintic. In reality, it gives an indication of the anthelmintic inefficiency. It does not necessarily indicate AR or otherwise, as other factors influence the test result (see notes below).

    Taking the test

    There are two stages involved. Stage one involves taking faecal samples prior to dosing lambs.

    This is followed by a sample taken some time after dosing to check if the treatment was effective or not. The procedure for taking stage one and stage two samples are described below.

    Stage 1

    1 Farmers must contact a laboratory to request sample containers, allowing time to arrive by post before sampling.

    The list of approved laboratories is available on DAFM website or from your adviser.

    2 Randomly select 15 lambs and place in a clean pen.

    Identify the lambs by marking them, allowing the same lambs to be identified one to two weeks later. Leave them time to defecate (to pass faeces) for up to one to two hours. Take samples as soon as possible after gathering. Lambs should not have been dosed for at least six weeks prior to sampling.

    3 Using gloves, collect fresh faecal samples from at least 10 separate fresh faecal deposits and place them in 10 separate containers.

    Make sure to collect more than a teaspoonful of faeces, but do not overfill the containers.

    4 Lambs must be treated with anthelmintic on the same day as the stage one faecal samples are collected.

    Treat the 15 lambs with an anthelmintic from one of the following: White (Benz imidazole (1-Bz)), Yellow (Levamisole (2-LV)) or Clear (Macrocyclic Lactone (3-ML)).

    Check the expiry date of the product. Follow manufacturer’s instructions. Check that the dosing gun is working properly and that the dose is administered correctly.

    Ensure the lamb swallows the entire dose. Dose all lambs at rates according to the weight of the heaviest lamb in the group.

    Do not use a dual active wormer with ingredients from more than one of these groups. Do not use a new-generation wormer (e.g. Zolvix or Startect)

    5 Complete form STAP 3A, recording the name and the anthelmintic class that was used. Place all filled containers of faeces, plus the complete form, in the plastic zip-lock bag provided.

    6Package and post the samples, preferably on the day of sampling

    Take samples early in the week to avoid being in the post over the weekend. Place in a fridge if being kept overnight.

    Stage two

    1 Seven or 14 days after the initial test and dose, depending on the anthelmintic product used (see below), gather the lambs again for faecal sampling.

    

    2 Re-sample the same 15 lambs using the guidelines one to three from stage one and post samples to laboratory according to steps five and six above.

    The results will be reported to you and to DAFM after all procedures are complete (i.e. both stage one and two complete).

    Interpreting test one

    Parasites identified on the STAP faecal test

    For the purposes of task three under STAP, most of the approved laboratories report on the level of eggs present in faecal samples for the following:

  • Strongyle worms, which include mainly Trichostrongylus, Cooperia and Teladorsagia spp.
  • Nematodirus spp.
  • Coccidial oocysts.

    • While Cooperia are not particularly pathogenic and, in general, are of little concern, their eggs are similar to the other strongyle eggs and they will contribute to the FEC.

    Some laboratories are also reporting on the number of:

  • Strongoloides, which is a threadworm and is far less pathogenic and should not be confused with the Strongyles.
  • Moniezia, which is a tapeworm and again not of major concern.
  • Lungworms, (including Dictyocaulus sp.) and is generally of low significance.

    • Strongyle species

    Having taken sample one of the test, lambs will have been dosed after sampling and before receiving the test result.

    The main worms of concern for lambs from 1 June onwards are the Strongyle worm species.

    The message to be taken concerning Strongyles from this first test is summarised in Table 1.

    Nematodirus spp.

    Assuming that by mid- to late-June lambs will be greater than 10 weeks old, a high egg count for Nematodirus is probably of little significance because:

  • Lambs tend to become resistant to Nematodirus from 10 to 12 weeks of age.
  • Egg production tends to be high when numbers of larvae in the gut are low.
  • There are several species of Nematodirus, with Nematodirus battus being the only pathogenic species for lambs. The worm eggs identified in the egg count may also include non-pathogenic species.

    • However, if lambs show signs of black scour, straining, dehydration, generally being unwell, Nematodirus could be causing the problem and a dose may be justified.

    Furthermore, a dose may be considered to reduce the worm egg burden being passed onto the pasture for next year.

    Coccidia

    Where the levels of coccidian oocysts are high, there may or may not be a problem.

  • Lambs tend to be infected with small numbers of coccidian parasites and develop immunity to these parasites from about eight weeks of age onwards. However, the immunity will not develop if the lambs do not have some exposure to coccidia. Furthermore, husbandry and management may lead to high challenge and even immune animals may develop clinical symptoms.
  • As with Nematodirus, there are several species of coccidia that are non-pathogenic and these may give rise to the high oocyst count in the test.
  • On the other hand, the coccidia present may, in fact, be pathogenic. Therefore, if there is an unexplained scouring or lack of thrive, the results should be discussed with a veterinary surgeon as coccidia may well cause a problem.

    • Other species identified

    Strongoloides, Moniezia and Dictyocaulus spp. are far less pathogenic in sheep than the groups of parasites discussed above.

    High egg counts should only be of concern if there is some unexplained problem, such as excessive coughing among lambs (not common), which may be associated with a high level of lung worms.

    Interpreting test two

    The purpose of taking the second test is to determine the efficacy of the anthelmintic used following the taking of the initial test.

    Therefore, the result of this test must be examined in conjunction with the first test.

    The proportional reduction in egg count is important. While dosing is generally not recommended at counts of less than 500 strongyle eggs per gramme, the proportional reduction in egg numbers can be calculated at much lower counts, as outlined in Figure 1.

  • If the result is > 95%, it is considered there is no problem with the anthelmintic
  • If the result is <95%, it is considered there is a problem and anthelmintic resistance is likely if dosing guidelines were adhered to correctly.

    • Decisions based on result

    Whether participating in STAP or not, faecal egg counts are very useful and can provide valuable information. They can be used to:

  • Help determine whether animals need to be treated or not.
  • Help time treatments better.
  • Test the efficacy of the treatment.
  • Reduce the number of treatments where anthelmintics are used excessively.
  • Obtain information on the level of contamination going onto pasture.

    • Table 2 provides a guide to interpreting low, medium and high faecal egg counts in lambs in terms of eggs per gramme for the main pathogenic roundworm species in Ireland.

    When Strongyle worm egg counts are in the medium to high category in lambs during the early summer months, a dose is usually justified.

    * Frank Hynes is a sheep specialist, with Teagasc, based at its Animal & Grassland Research and Innovation Centre, Mellows Campus, Athenry, Co Galway