Hot, dry conditions have kept worm burdens on grazing paddocks at a relatively low level over the past month.

However, with rain in the forecast for the week ahead, worm populations will begin to increase rapidly.

Therefore, keep a close eye on cattle for signs of a worm burden in the next fortnight and move in with some form of treatment before animal performance drops.

1. Which cattle to treat?

Young stock in their first grazing season are at most risk, so pay attention to spring- and autumn-born calves.

Yearling stores in their second grazing season are also at risk, followed by in-calf and first-calved heifers.

Mature cows should have developed resistance to gut and stomach worms. If mature cows are struggling to gain flesh, fluke may be the problem rather than worms, so consult with your vet.

2. Choosing the right wormer

There are lots of wormers to choose from. Don’t just go for the cheapest product on the shelf.

Wormers are generally classed as white drenches (benzimidazoles), yellow drenches (levamisoles) and clear drenches (avermectins).

Some cheaper products require a bigger dosing rate. Some expensive products require a small dosing rate to be administered. On a per-head basis, there may be little cost difference.

Gut worms are normally more of a problem in the early summer, with lung worm being more common from mid-summer onwards.

Pay attention to the active ingredient in wormers, which is the chemical that target parasites, as well as withdrawal periods if store cattle are likely to be killed off grass this summer.

3. Dosing technique

Cattle should always be secured in a crush, or race, when dosing so the product guidelines can be followed properly. Do not attempt to apply a pour-on to animals standing freely in a loose pen.

When using oral drenches, a head scoop will improve the accuracy of the dose administered. A long-reach hook is also recommended.

With injected wormers, check if the dose should be given into the muscle or under the skin and change the needle regularly.

4. Grouping cattle when dosing

Ideally, cattle would be weighed individually when dosing so each animal get the correct rate. But this is not an option for the majority of farms.

As an alternative, try filling the crush race with cattle of even size on every pass. This should cut down the variation in liveweight. Once the race is full, set the dosing rate to the heaviest animal in each pass.

5. Rotating wormers

Do not use the same wormer every time cattle are being dosed. Change wormers every so often to reduce the build-up of anthelmintic resistance.

This means choosing a wormer with a different active ingredient, rather than a different brand name.