The routine use of highly effective anthelmintics (wormers) combined with grazing management has controlled worms successfully in the majority of UK sheep flocks for nearly 40 years. However, this reliance on chemical treatment comes a cost - and that cost is the development of resistance to anthelmintic chemicals used.
In other parts of the world, such as South America and South Africa, the extent of this resistance is much more serious than in the UK. However, the number of cases here have risen sharply in recent years, with an increasing number of flocks finding that one or more of the chemical groups are no longer effective against some worm species.
Act now, before it’s too late
The good news is that if you take action now you can extend the useful life of the older anthelmintic groups. Resistance is not black and white. It develops over a number of years and the number of worms killed gradually reduces. Testing to find out which wormer groups are effective will prevent you wasting time and money. It also means lamb performance is protected from untreated worms. Carefully integrating the two newest groups (4-AD orange and 5-SI purple) into your control programme is also an essential step.
The main challenge is to take action before you have a tangible problem with resistance. If you wait until it is forced upon you, it will be too late and your option and ability to control worms will be very limited.