Good Practice

Good Practice based on Current Knowledge

Breed sheep with a known resistance to helminthiasis.

Use forage crops with high quality protein, such as sainfoin and lucerne, strategically, to increase the resilience of the lambs to helminthiasis and possibly increase their immunity.

Botanical or other alternative dewormers may be useful in the control of low worm burdens.

Where possible, graze cattle alternately with sheep.

Lower stocking density.

On lowland farms use clean grazing for the lambs.

On organic hill and upland farms, where clean grazing is not available and parasitic gastroenteritis in lambs is a problem, ewes may have to be treated with anthelmintics (obtain permission) when leaving the lambing fields or at turnout to prevent the periparturient egg rise. Use anthelmintics which also kill arrested larvae. Do not use the AV class of antheminthics, with the exception of moxidectin.

Where Nematodirus is a problem, prevent the lambs from grazing fields grazed by lambs or calves in the previous year. Obtain the nematodirus forecast from MAFF.

In the case of unacceptable levels of helminth egg output, the lambs have to be drenched with an anthelmintic on the advise of the named veterinary surgeon.

Anthelmintic drug resistance is a real concern, and The Moredun Foundation has recently released ground rules, some of which may apply to organic farming, to delay the development/transmission of anthelmintic resistance (Jackson and Coop, 1999):

Reduce the frequency of drenching. Consult your veterinary surgeon or sheep advisor for advice on the optimum number of drenches needed per season. Frequent suppressive drenching has been shown to increase the rate of selection for anthelmintic resistance, as it allows only resistant worms to pass eggs onto the pasture.

Adopt a rotation of anthelmintic classes. Resistance to an anthelmintic is more likely to occur if the same class of wormer is used without any change. It is a good policy to adopt an annual (not more frequent) rotation between BZ and LV classes of drugs to reduce the selection pressure for development of resistance. However, it may be necessary to use specific drugs for the control of tapeworms and sheep scab at certain times of year.

Ensure the use of the correct dose rate. Follow the manufacturer's instructions and do not mix different wormers together. Increase the efficacy of the drench by applying it over the back of the tongue and not just in the mouth. This will ensure the anthelmintic enters the rumen instead of entering the abomasum via the oesophagial groove. Efficacy can also be improved by short-term withdrawal of feed. However, ewes in late pregnancy should not have their feed withheld, due to the risk of inducing pregnancy toxaemia.

Check that the drenching equipment is accurate. Calibrate regularly.

Check stock body weights and dose to the heaviest animals within the group being treated. It is better to slightly overdose than underdose.

Use grazing strategies to reduce pasture contamination/hot exposure. Provision of 'clean' or 'low-risk' pastures such as new leys or aftermaths and grazing using adult non-lactating ewes or cattle can reduce the parasite population on pasture and hence the requirement for frequent drug treatment.

Avoid importing resistant worms: Since most anthelmintic resistance in the United Kingdom is against the benzimidazole class of drugs, treat all purchased stock on arrival on your farm using drugs from the LV class of anthelmintics or with moxidectin. If possible, hold new stock in a yard for at least 24 hours after dosing before turning out onto pasture to reduce contamination of grass with worm eggs.

Do not graze sheep and goats together, as goats more commonly have resistant parasites.

Where resistance is suspected: Seek assistance to check the efficacy of your drench. The veterinary surgeon can organise a simple faecal egg count reduction test to check the efficacy of the anthelmintic. It is worth noting that continued scouring after treatment might indicate that other infections such as coccidia could be a contributory factor.

If resistance is confirmed:

- Discontinue the use of the class of drenches to which resistance has been demonstrated.

- Alternate annually between the remaining effective drench classes.

- Periodically test that these products are still effective.

- Use management strategies which minimise the number of treatments per season.