Getting to grips with worming

With resistance to anthelmintics increasing nationally, deciding what product to use and when to use it can be mind-boggling, but it needn’t be. Your vet can work with you to create a tailored worm control plan specific to your farm.

Choosing the correct product is not only important in slowing down the rate of anthelmintic resistance (AR), but also in optimising sheep performance in a cost-effective way. SCOPS have produced a “Know Your Anthelmintics Group” guide, which lists and classifies all anthelmintic products. If we know what we are wanting to treat, we can choose the correct product to produce better results with less need for repeat treatments. Narrow-spectrum products are superior to broad-spectrum (e.g. combination products) as they do not select for AR. Product choice also depends on any previous AR history on your farm, in which case your vet will work alongside you to put alternative control plans and treatments in place.

Tips on treating correctly

  1. Weigh DON’T guess!
  2. Calibrate and maintain the drenching gun. ALWAYS check the gun is working effectively and delivering the right amount before you start.
  3. Drench correctly – the nozzle should be placed between the incisor and molar teeth over the back of the tongue with the sheep’s head adequately restrained.
  4. If using injectables, ALWAYS follow manufacturer’s instructions.

There are two main approaches to anthelmintic treatments on farm: strategic dosing vs. targeted dosing.

  1. Strategic dosing aims to reduce pasture contamination and therefore subsequent treatments in the early grazing season, but over time can lead to AR, so monitoring for resistance is essential!
    For example: worming ewes at lambing when they undergo peri-parturient rise and their immune systems relax. Worm egg output increases in ewes largely without causing clinical signs which increases pasture contamination, producing high infection pressure to naïve lambs when they begin grazing. Worming ewes at lambing reduces the egg output, lessening this risk. However, because AR is increasing rapidly, it is recommended to treat only ewes with a poor BCS (<2.5), ones that have had triplets or large litters and first time lambers. This ensures that there are some susceptible worms passed onto pasture to dilute out any resistant ones. This approach is altering and adapting more towards a combination of strategic and targeted dosing.
  2. Targeted dosing aims to avoid the use of anthelmintics unless needed via undertaking Faecal Egg Counts (FEC); monitoring parasite forecasts and observing key performance indicators (KPIs: BCS, daily live-weight gain, fleece condition).
    For example: routinely undertaking FEC in fat lambs during the summer grazing period. If FEC results suggest a significant worm burden, the group should be wormed, ensuring that the fittest in the group (10-20%) are left untreated to reduce AR. However, if a FEC indicates minimal worm burden, treatment can either be avoided altogether or targeted at poorer lambs only. This will save on both labour costs and cost of the wormer itself.

Both NADIS and SCOPS parasite forecasts consider regional temperature and rainfall data in order to predict when peak hatches of eggs may occur; therefore, highlighting the biggest risk periods and locations.

FEC is an invaluable tool in monitoring worm burdens, indicating when treatment is required and checking treatments are working effectively. Some practices offer this in-house, but there are also external labs that offer the service. You should follow recommended guidance when collecting muck samples; they should be as fresh as possible (still warm!), in a plastic/clean container and should be examined within 48 hours of collection. In old samples, some eggs will have hatched and the results may be an underestimate of true worm burden.

FEC sampling

  1. Gather the sheep for 5-10 minutes.
  2. Wear disposable gloves and collect dung samples from at least 10 animals (ideally 10% of the group if possible).
  3. Pool the sample together if wanting to assess a group rather than individual and aim to fill a 30ml sample pot.
  4. take the sample to the practice where they may be able to carry out the FEC in house or send off to an external lab.

Testing for resistance is fast becoming a welcomed tool in the sheep industry. There are different ways to detect AR, but the most common method is ‘Post-Drench FEC’. From a group of animals recently treated, 10 should be selected. Time after treatment depends on the product used (white: 10-14 days, yellow: 7 days and clear: 14-16 days) and it is worth noting that this test is only an indicator of ineffective treatment not AR. The usefulness, however, is increased if muck samples are submitted for testing on the day of treatment and the specified time after treatment to provide an estimate for FEC reduction. Post-Drench FEC should be repeated throughout the season as part of ongoing monitoring in line with Flock Health Plans.

Due to rapidly growing reports of resistance, SCOPS have issued specific advice on long-acting moxidectin 2% products to retain and preserve its use as an anthelmintic and scab treatment. Annual use is no longer recommended in ewes around lambing. If used, it is essential to leave 10% MINIMUM untreated (these should be spread across different grazing groups). Where moxidectin 2% products have been used in ewes at lambing, OP-dips should be used to treat scab.

Quarantine treatments aim to minimise introduction of any resistant worms to your farm when purchasing stock or when bringing home stock back from areas with an unknown AR status.

Simple quarantine strategy:

  1. Yard all sheep on arrival for 48 hours. This ensures that contaminated faeces are not dropped onto your home pasture.
  2. Treat with a Group 4 (AD – Orange) or Group 5 (SI – Purple) product to try and remove any worms resistant to the common groups.
  3. Turnout to contaminated pasture (has had sheep on this season). If any worms survive the quarantine treatment, we don’t want them contaminating any clean pastures. Also, incoming sheep need to be exposed to the worm population on your farm.

If you are concerned that worms may be posing a significant threat to animal welfare and economic losses on your farm, please speak to your vet to investigate these issues. REMEMBER… each farm is different so one worm control plan will not fit all!