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  • Writer's pictureFlockFinder Team

FlockFinder Guide to Worming 🪱

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What are Worms 🪱?

Worms are the most common health problem suffered by domestic sheep and present a major threat to the performance and health of lambs.

There are many different types of worms that can cause problems to sheep, but stomach worms are the most common. Stomach worms cause many symptoms in sheep and lambs including weight-loss, poor growth rates and can result in death if the symptoms go undetected.

Data shows that lamb growth rates can be reduced by up to 50% 📉 due to worm burden, with no immediately visible sign that the lambs are unhealthy.

Controlling worms has therefore become an essential part of modern farming with the industry becoming increasingly dependent on anthelmintics. However, worm resistance is increasing, is irreversible, and threatens all farms in the UK.

Worm resistance is an invisible problem, only becoming visible when it's too late.

Research from Wales Against Anthelmintic Resistance Development (WAARD) has shown that:

However, despite this, 86% of farmers thought their wormers were working, primarily based on the look and condition of the sheep.

Do my sheep have worms 🤷‍♂️?

Most flocks have worms with weight-loss and poor growth rates being typical signs of worm presence, however, worm burden can often present no visible signs that the lambs are unhealthy.

Fortunately, the presence (and quantity) of worms can be confirmed by a simple Faecal Egg Count (FEC). These tests are affordable (~£8-10/test), readily available, and provide a reliable result.

It is important to use FECs to check ewes and lambs worm status, and drench only if required. It is recommended to conduct FECs every 3-4 weeks throughout the grazing season, to keep on top of the worming needs for your flock and identify the optimal time for treatment. TEST, DON'T GUESS.

FECs can also be used to determine if a given group/class of wormer is working and whether there is an increase in worm resistance. This is also known as drench-testing.

The aim is to use anthelmintics less often with maximum impact on the worm population. Correct drench administration is also very important, with dosages appropriate to the weight of the sheep.

Check out our Guide to Drenching for advice on how to drench effectively.

How to do a FEC 💩

Taking a FEC is simple and quick once you know what to do.

  1. Use fresh ‘samples’, ideally less than an hour old. If its still warm to the touch its still pretty fresh! Always wear gloves and wash your hands afterwards. Take at least 10 individual samples per group.

  2. If you are combining individual samples to send a group sample, then each individual sample must be the same size in order for the result to be representative.

  3. Sheep should be healthy and have had full access to pasture and/or feed before sampling.

  4. Samples taken must be completely random. Do not mix ewe and lamb samples when testing unweaned lambs.

  5. Make sure the container is airtight (expel excess air if using a bag) and keep the sample cool. Samples must get to the lab within 48 hours, so don't post over a weekend.

TOP TIP: Gather your sheep into a corner of the field, or pen, holding them for a few minutes, then collecting the fresh dung when they move away.

The AHDB has produced a video to help guide you through the process:

The results will give the number of worm ‘eggs per gram’ (EPG) of faeces. The number acts as an indication of the number of adult worms present in the gut of the sheep and can be used to:

  • Tell if a treatment has been successful

  • Help tell if a group of animals need to be treated

  • Provide an indication of the level of contamination on a pasture

When should I drench my flock 🕑?

You're in luck, we've pulled together a handy worming guide👇 so you know when you need to drench, and when you don't. A PDF version is available to download at the bottom of the page.

To check whether a treatment has been effective, a drench-test should be completed. The length of time after treatment to do this test is dependent on the wormer group used. Typical timings are:

  • 1-BZ (White): 14 Days

  • 2-LZ (Yellow): 7 Days

  • 3-ML (Clear): 14 Days

  • 4-AD (Orange): 14 Days

If a treatment has not been effective 😔 (i.e. you are still getting high EPGs) then it is possible your flock might be showing some resistance and you should discuss options with you VET.

DON'T FORGET to record the treatments in your medicine book📕. If you often forget to do this, then download FlockFinder today and record treatments while out in-the-field. Bulk treatments (like drenching) can be quickly and easily recorded with just a few taps in our app and your medicine book will be kept up-to-date! It's that simple! Get started today with our 30-day free trial!

Tips to reduce your worm risk 🤔

Ensure that wormed lambs are not moved directly to clean pasture. Retain lambs on original pasture for 48 hours to dilute the effect of any resistance.

SCOPS, Sustainable Control of Parasites in Sheep, advises effective quarantine of ALL sheep brought onto the farm as a critical measure to protect against resistant worms. Assume ALL incoming animals are carrying resistant worms and treat with a 4-AD or 5-SI anthelmintic. Perform a FEC to check efficacy of anthelmintic treatment 14 days after use. Keep ALL incoming sheep isolated from the rest of the flock, turn out onto separate pastures that have been grazed by the resident flock (where possible) for 3-4weeks. Incoming animals can join the resident flock. The full SCOPS guidance can be found here.

SCOPS also provides guidance on the use of 4-AD (Orange) and 5-SI (Purple) anthelmintics here.

Along with general guidance on anthelmintic types and usage which can be found here.

FlockFinder Worming Guide (PDF Download)

FlockFinder Worming Guide
Download PDF • 69KB


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