We can thank the Sheep Technology Adoption Programme (STAP) for raising the awareness of worm control on sheep farms and bringing about some change in how participating farmers approached worm control.

STAP also, however, showed some worrying results, with resistance to the anthelmintic classes benzimidazole (1-BZ), levamisole (2-LV) and macrocyclic lactones (3-ML), found in commonly used products, higher than anticipated. Some farms had resistance problems with one of the three classes, while, of more concern, some flocks had resistance to all three.

The STAP faecal egg test (Task 3) was therefore very worthwhile in establishing the efficacy of treatments and establishing if resistance was in fact a problem. It also highlighted flaws in many worm control programmes, which meant animals were incorrectly treated. Over time this is contributing to the rate of resistance developing.

Summer focus

While anthelmintic resistance is not an attractive subject, the focus this summer should be to implement a worm control programme that ensures high levels of animal performance and at the same time protects your flock from anthelmintic resistance developing further.

Faecal egg counts are a useful way in determining the need for dosing, but even where this is not practiced, there are a number of practical steps that can be taken. These are summarised in Figure 1 as follows.

  • Choose an appropriate anthelmintic: Worm- control products are relatively cheap, with a high number of products on the market. While some farmers have the best intentions in alternating between products, mistakes are commonly made in switching between products, but not actually selecting a product with a different active ingredient. Decisions should therefore concentrate on going beyond the product name and looking at the active ingredient or anthelmintic class.
  • Read the manufacturer’s guidelines carefully: This may seem like a tedious step, but different products have different recommendations. For example, some combination worm and fluke products have different treatment rates for the ailment treated. Guidelines will also contain useful information about the need to shake the dose regularly to prevent settling, storage information and, most importantly for many farmers during the summer months, the withdrawal date.
  • Calibrate the dosing gun: A significant problem on many farms leading to incorrect treatment is not the selection of an unsuitable product or anthelmintic resistance, but rather under-dosing. Your dosing gun should be calibrated regularly to identify if it is delivering the recommended amount. This can be easily achieved by dispensing a few doses into a measuring cylinder. Dispense more than one to check that the gun is refilling correctly. Washing the gun regularly with hot water will help keep it working properly.

    If the inside of the barrel is stiff, applying a small amount of cooking oil will help lubricate the fittings without contamination.

    Dose to the correct weight: A lamb’s weight can be deceivingly variable depending on its age, level of fat cover and stage of the season. Weigh the heaviest three to four lambs in the group and dose according to this weight. Where a significant difference is present, it is worth splitting the group for treatment and getting a second weight to dose lighter or younger lambs to.

  • Correct delivery: The product should be delivered to the back of the animal’s tongue. The gun should be inserted at the side of the mouth and the animal should be securely restrained to prevent it jumping up and risk damaging the lining of its throat with the dosing gun.

    • Faecal egg counts

    Ideally, worm control should take place based on the results of faecal egg count tests. The practice is money well spent when you consider that you may be spending money treating lambs that do not need it.

    A reason often made for dosing lambs is that lambs are scouring or loose in the dung. While it may well be the case that lambs possess a worm burden, research carried out also shows that lambs can be scouring without possessing any parasitic burden.

    A faecal egg test can be carried out by flocking sheep and collecting a pooled fresh sample of faeces from about 10 lambs randomly from the group.

    The sample is sent to a laboratory for testing, with a result returned anywhere from the same day of delivery to a couple of days later. This practice will determine if lambs need worm control treatment.

    If the aim is to establish the efficacy of an anthelmintic class, then a faecal egg count reduction test needs to be carried out, which is summarised in Table 2 and detailed below.

    Important considerations

    There are a number of factors to consider to ensure accurate diagnosis. It is important that only fresh samples are collected.

    Do not delay in getting samples sent. Where a delay occurs, samples should be stored at a low temperature (ideally in a fridge) to prevent eggs hatching out and giving an inaccurate result.

    If posting, make sure to send early in the week so that samples arrive for processing or storage and are not sitting over the weekend in a warm area that increases the risk of eggs hatching.

    Also, securely package samples as detailed below to prevent any spillages.

    Egg count reduction test

    The protocol to establish the efficacy of an anthelmintic as recommended through STAP is as follows:

    1. Farmer must contact laboratory requesting empty sample containers and also arranging a payment procedure. Lambs should not have received treatment in the previous six-week period to collecting samples.

    2. Place lambs (minimum of 15) in a clean pen. Leave them undisturbed for a couple of hours (to defecate). Remove lambs from pen.

    3. Using gloves, collect fresh faecal samples at random from at least 10 different faecal deposits and place them separately in the containers provided (it does not matter what amount you collect as long it is more that a teaspoonful, is fresh and each sample is kept separate). Large amounts are not desirable either.

    4. Place all filled containers in the plastic zip-lock bag provided.

    5. Put in the post as soon as possible, preferably on the day of sampling. If there is a delay in posting, then store the samples in a cool place, preferably in a fridge (do not freeze or place in direct sunlight).

    Dosing protocol

  • Choose an anthelmintic that you wish to use.
  • Dose in accordance with manufacturer’s recommendations.
  • Check calibration of dosing gun or syringe.
  • Check expiry date of drug.
  • Shake bottle or container well.
  • Weigh the three heaviest lambs in the grazing group being tested.
  • Dose all lambs at rates according to the weight of the heaviest lamb in the group.
  • Record the name of the product you used and which anthelmintic class it belongs to.

    • Repeat sampling

    The faecal collection process should be repeated seven days later if testing for resistance to levamisole or yellow drenches and 14 days post-treatment if testing for resistance to benzimidazole (white drenches) or macrocyclic lactones (clear drenches including ivermectin).

    Treatment decisions

    Table 1 details a guideline to interpreting faecal egg counts that has been previously included in an article written by Teagasc sheep specialist Frank Hynes.

    Frank has put together a lot of information for farmers, including the videos below.

    The general recommendation if using faecal egg counts to determine the need for dosing is that there is no need to treat at counts of less than 500 eggs per gramme, with another faecal egg count recommended two to three weeks later.

    Table 2, Figure 3 and Figure 4 give an explanation of the result obtained in the faecal egg count test and is based on the proportional reduction in egg numbers.

    If the result is >95%, it is considered there is no problem with anthelmintic resistance while if the result is <95%, it is likely that there is an issue with resistance, provided the recommended dosing guidelines were followed during treatment.