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Parasite Control in Sheep

Stephanie Patel BVetMed MRCVS, Molecare Farm Vets

We all know the consequences of worm burdens in sheep, loss of condition, poor weight gain, and even death, but are we controlling it properly? What are we basing our decisions on when it comes to worming them? Is it being dictated by price, the leftover products you have to hand on farm, or a recent Faecal Egg Count (FEC)?

Hopefully the answer to the above should be FEC, and if not, it should be! We wouldn’t just decide to inject an animal with an antibiotic based on the way it looked, a clinical examination would be done, and a temperature check carried out to see if it is raised due to an infection. With the increasing awareness of antibiotic resistance in both the human and animal world, we have become more careful in what and when we use antibiotics, and the same should be applied to wormers. 

There is an increasing resistance to wormers, and we should be worried.  A study conducted in the South West in 2017 found that white wormers were ineffective on 96% of farms, and clear wormers were ineffective on 67% of farms.  Overall it was found that 40% of farms were found to be resistant to all three categories of wormers (white, yellow, and clear).  This has no doubt increased since the study was conducted, so what can we do about it? How can we reduce resistance occurring on our farms?  The good news is that it is never too late. Steps can be taken to reduce resistance occurring and being brought onto farms. The following are the SCOPS (Sustainable Control of Parasites) principles which should be followed:

1) Making sure the product you are using is effective.

This includes the following:

  • Calibrating the gun and making sure that the dose you are giving the sheep is being accurately administered by the gun is important.
  • Dosing to the correct weight, using the right product at the right time. 
  • Ensuring that the product you are using is effective on your farm. This can easily be done and is known as a drench test.  Samples are taken pre and post worming and for the product to be effective there should be a 95% reduction in the number of eggs.

2) Use management and monitoring to reduce reliance on wormers.

The use of FEC is what we should be basing our decisions on whether to worm a group or not.  Adult sheep should not be over wormed as they have a developed immune system which can cope, and therefore can be used to reduce pasture contamination. Worming should therefore be done strategically with the adults at the right time. Nutrition also plays a significant role, with those who are thin being less likely to cope with a burden, along with pasture rotation and stocking densities having an impact too.  It is also worth mentioning that certain crops such a chicory and birdsfoot trefoil can reduce worm burden in sheep.

3) Avoid bringing resistant worms onto farm.

All new stock that is brought onto farm should be quarantined, following a strict protocol regarding which products to use, and when. For more information on quarantining your sheep, you can read our article here: https://www.molecarevetservices.com/the-importance-of-quarantining/

4) Minimising the selection of resistant worms when sheep are treated. 

It is important that you do not dose and then move your sheep. Turning them back onto the pasture they were already on will mean that resistant worms can be ‘diluted’ by the non-resistant worms before moving them to new ground. Alternatively, do not treat the whole group. Using products (when appropriate) late season to knock out the resistant worms that have built up over the grazing season. 

Remember next time you’re using a wormer, you are not treating the sheep, but treating the worms within, and each time you use it, you are slowly increasing resistance by exposing that worm to the product.                    

For more advice on worming protocols, please speak to your Molecare Vet by calling 01392 872934

Reference: Glover, M., Clarke, C., Nabb, L and Schmidt, J (2017) Anthelmintic efficacy on sheep farms in south-west England.  Veterinary Record doi: 10.1136/vr.104151 Sustainable Control of Parasites (SCOPS) https://www.scops.org.uk/

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