Worming In Sheep
Roundworm infestations in the gut represent one of the most common causes of production loss in UK sheep
flocks. Most farmers treat their flocks repeatedly with wormers in an attempt to control the disease. Unfortunately, repeatedly worming sheep has led to the development of resistant worms that cannot be killed by wormers. The type of wormer, the dose, the time of year and which sheep are wormed on the farm are all important factors which affect the resistance of worms to wormers. This is why a properly thought out worm control plan could improve profitability and minimise worm resistance on your farm.
Adult sheep generally have good immunity to worms, with the exception of ewes around lambing time (the stress of ewes at lambing time effects their natural immunity resulting in worm eggs being shed onto the pasture in much greater numbers at this time). Ewes should only be wormed once a year at lambing time; this will reduce the number of eggs on the pasture so that there are less for lambs to pick up.
Lambs have little resistance to worms in their first grazing season but this develops with time. Strategic worming of lambs with the correct wormer is essential to maximise profitability.
The new worming recommendations fall into two general categories:
1. Basic Good Practice: using anthelmintics properly and effectively to get the best from each treatment. Preventing the importation of problems to your farm and choosing the right product.
2. Reducing Selection Pressure: avoiding the over-use of anthelmintics, implementing other practices to help reduce the challenge from worms and limiting actions that select heavily for resistance, such as drenching directly on to a clean pasture.
The following points summarise the main things sheep producers should now consider when planning their worm control. Points 1-6 are straightforward and relatively easy to implement. However points 7 and 8 are more complex and will require time and discussion with your vet or adviser.
1. QUARANTINE TREATMENTS
Not all farms have resistant worms so quarantine treatments are vital to ensure that any in-coming sheep don’t bring resistance with them. Follow these three steps:
A – Choose a treatment option from the choices in the SCOPS guidelines
B – Keep them off pasture for 24-48 hours so that all the worm eggs have been passed.
C -Turn them out on to dirty pasture to make sure any eggs form worms that may have survived treatment are diluted by worm eggs already on the pasture
2. ALWAYS ADMINISTER DRENCHES CORRECTLY AND AT THE RIGHT DOSE RATE
Always dose to the heaviest in the group don’t guess, weigh them! Then check that the dosing gun is working properly by discharging it several times into a syringe or measuring jug. Make sure that the drench goes over the back of the tongue and where possible restrict access to feed before administering 1-BZ (white) or 3-ML (clear) drenches (but never for pregnant ewes).
3. TEST FOR RESISTANCE
Find out which drenches are working effectively on your farm by taking faeces samples before and at a set number of after treatment (2-LV = 7 days; all others 14 days). Ask your vet for details of how this simple test can be done. Then plan a strategy that takes account of your current resistance status with the aim of maintaining the effectiveness of the chemical groups that are still working.
4. LOOK AT YOUR CONTROL STRATEGY
Are you drenching to a set pattern every year? If so, it’s time to sit down and look at the reasoning behind each treatment and whether there is scope to reduce the number of treatments or to target them better. Consult your vet or adviser and look at how you can implement these recommendations. Some strategies can be put into practice quickly, while others will take time, but the sooner you act the longer the drenches will work for you.
5. REDUCE DEPENDENCE ON ANTHELMINTICS WHERE POSSIBLE
Looking for ways to use other strategies such as grazing management to reduce worm burdens remains an important part of worm control. Pasture such as aftermath, areas grazed by cattle or even fields that have just carried dry adult sheep will have lower worm burdens meaning lambs grazing them will require fewer treatments. The inclusion of bio-active forages in grazing swards is also an option and the advances being made with rams selected for resistance to worms may also offer the option to reduce anthelmintic use in the future.
6. TRY TO USE ANTHELMINTICS ONLY WHEN NECESSARY
Faecal Egg Count (FEC) monitoring has an important part to play in determining when and which sheep to drench. Sheep farmers who regularly use FECs use less drench overall and therefore reduce the selection pressure for resistant worms. Minimising the treatments given to mature sheep that are immune to most worm species is also important. If adult sheep are fit and healthy, the need to treat them is limited and some routine treatments such as ewes pre-tupping avoided for the majority of the flock.
7. SELECT THE MOST APPROPRIATE ANTHELMINTIC
Monitoring can also be used to show which parasites are present and this helps to reduce the use of broad spectrum anthelmintics. For example, liver fluke can be treated with flukicide products that do not contain any of the wormer groups. The Barbers Pole worm (Haemonchus contortus) can also be treated with a narrow spectrum wormer. This can significantly reduce the unnecessary use of the anthelmintics we need to preserve, particularly in adult sheep. It is also usually cheaper!
8. PRESERVE SUSCEPTIBLE WORMS
What we need to try to do is to avoid exposing more worms then is necessary to the anthelmintic. This is quite easy when sheep are on heavily contaminated pasture because there is a large proportion of the worm population on the pasture and these escape exposure. At other times, there is a risk that only a small part of the worm population is outside the sheep treated and this is highly selective for resistance. Ask your vet for advice about preserving susceptible worms.For the right worming advice for your own particular farm situation please consult your vet or usual animal health product outlet.
