Worming sheep in the Spring

Ewes

The first question that needs asking is – do the ewes really need worming?

In reality a lot of the ewes won’t need a dose in April. Some may have been treated at lambing but most ewes will have good worm immunity by now, so it is a waste of money treating them. Treating can also add to the possibility of worm resistance developing quicker.

Fluke is very different though. Ewes do not get immunity to liver fluke so it is possible that they may need a dose should the farm or weather conditions are favourable for fluke in the late winter/ spring period. Try to avoid using combination fluke wormers though because as previously stated you could be worming unnecessarily.

Lambs

Lambs will face different challenges. They have no immunity when born so will pick up worms as soon as they graze should worm larvae be present on the pasture. Worms are likely to be present if the weather conditions are suitable (warm and wet is ideal) and the pasture has been previously grazed by other sheep. If it is a fresh re-seed or the weather is dry, hot or cold then there will be very few larvae present.

Nematodirus is the first major challenge in the Spring normally and as its cycle is a little different to other worms it is certainly one to watch for. It is very much all or nothing and the larvae population on the pasture is very much dictated by the weather. A cold spell followed by mild, wet weather is ideal for a mass hatch. The lambs consume vast numbers of the larvae in a very short space of time and as this is what causes the damage the timing of treatment (a white drench is normally fine) is critical to avoid severe losses.

Later on in the Spring there can be stomach and gut worm problems. A faecal egg count can help in keeping an eye on what’s happening and give a guide as to when to drench. In hot, dry weather you may not need to drench at all. You should ideally change drenches and not just stick to the white drenches. White drenches tend not to be as effective nowadays (this can be checked with a drench test) due to resistance issues.

As lambs will possibly be going for slaughter in the early summer it is important to take care with the withhold periods as some are longer than others.

A local animal health advisor or vet can not only help with faecal egg counting and drench checking but should be able to help put together a suitable parasite control plan for your farm as they will have knowledge of the local challenges facing your flock.