Tools to Help Inform Worm Treatment Choice in Sheep

When it comes to managing worms in sheep, it is no longer acceptable to use anthelmintics routinely. While wormers have their place, they need to be preserved for use at the right time to stop the development of anthelmintic resistance.

There are several management factors you can implement to reduce a lamb’s exposure to worms, which will help inform when to treat and which product to use. They are:

• Map fields according to worm-risk. High-risk pastures are those that have carried ewes and lambs within the same year, whereas low-risk pastures are those that have been used to grow crops or grazed by cattle. Lowest risk pastures should be targeted for weaned lambs.
• Rotational grazing can help dilute the worm burden as well as mixed grazing with cattle, which can help reduce pasture contamination.

• Faecal egg counts (FEC) can be an effective way of highlighting worm issues before clinical signs appear. Samples should be taken from each grazing group at least once a month during the risk period which runs from about spring onwards through to autumn.
• Forecasting tools are a useful way to keep abreast with local risks and upcoming issues. They can be a good base to start conversations with an animal health care provider about managing the risk.
• Growth rate changes can give early indication worms may be an issue in a flock. This data used alongside faecal egg counts can be a powerful tool helping to target correct treatment to specific animals.

• Worming ewes with long-acting moxidectin around lambing has been found to prevent what is known as the spring rise. This is when ewes in late pregnancy are more likely to shed eggs as their immunity is lowered and can be the main source of pasture contamination for lambs later in the season.
• Selectively worming ewes at this time can help reduce pasture contamination and risk to lambs. However, it is vital not all ewes are wormed. Thin and multiple-bearing ewes shed more eggs, and these are the ewes that should be targeted. Fit and single bearing ewes should be left untreated- with at least 10% of a group left untreated.
• Persistent products should be used with care and year on year use in all ewes should be avoided. Speak to your animal health care provider for further information on what the right treatment strategy is for your farm.

Investing time and money into planning and using some of the tools mentioned in this blog can help save money in the long run- whether that is saving on treatment costs or by preventing a loss of production from worms.