Be Wormwise this summer


Be Wormwise this summer

The Wormwise messages may not have been prominent in recent times, but they are still valid, valuable and doable. Newsletters will be an important source of these messages, and the Wormwise web site will hold the store of information.

With summer looming there are actions that can be taken that will reduce the impact of worms on productivity and other actions that will reduce the selection for drench resistance.

In this issue:

Drench testing

Quarantine treating incoming stock

Planning grazing to reduce the worm challenge

Setting up a drench plan

Summer brings its own set of worm management challenges. It is a time when young stock dominates in priority and often in numbers. Managing worms over the summer months is critical to achieving production goals but it is also a time when drench resistant worms can flourish. The keys to managing this time of the year are monitoring and planning.

Drench testing

Most of the drench that will be used in one year on the farm will be used over the next three or four months. It makes sense to know that the drench being used is totally effective. Using a 90% effective drench will give no signs of anything being out of place. But the lowered weight gains by using such a drench in young animals could be as much as 15% or greater. Therefore knowing which drenches not to use is vital to achieving maximum production. Drench testing will give this information. It also allows the best combination drench choice to be made by knowing how well individual drench families are working.

A drench test (also known as a Faecal Egg Count Reduction Test or FECRT), is best done early in the season. It is usually easier to get high faecal egg counts earlier, and all of the worm species existing on the farm are more likely to be present in lambs or calves early on.

Set up before the summer with whoever is going to manage the test so that the time to leave a group of lambs or calves not drenched can be targeted.

The test will require a minimum of 60 lambs or calves. The actual number depends on how many of the drench families and combinations are going to be tested. Once these test animals have high enough faecal egg counts to begin, the test duration is

10 to 12 days.

Quarantine treatment for incoming stock

If a farming system imports a lot of young animals, there is a high risk they will bring with them worms resistant to the drenches being used. Lamb or weaner calf/bull finishing operations face a high risk of introducing worms able to survive multiple drench families because the animals can come from many other farms.

It is crucial to put an effective quarantine treatment procedure in place to ensure any farming operation is protected.

The full quarantine treatment endorsed by Wormwise is:

1. Drench on arrival with:

Zolvix or Startect for lambs

A triple combination drench for calves

2. Hold animals off pasture for 24 hours.

The eggs from worms living in the animals when they arrive will take several days to emerge, but most will be excreted after 24 hours. It is important these eggs are deposited in a place where they cannot complete their lifecycle. A holding yard is ideal. Top finishers successfully use feeding racks off the ground and water troughs in yards to facilitate this process.


Graze animals on “old” pasture for the next three days or more.

It is important to expose animals to “resident” worms after the 24-hour quarantine period. This will dilute any worms that survive quarantine drench treatment and minimise the risk of them adding to the farm’s resident worm population.

Grazing planning

A contamination/exposure cycle can easily be created in young stock grazing systems on pastures. As the season goes on the level of worm contamination on the pasture increases so that the challenge to the young animals increases. In the face of high larval challenge from the pasture the weight gains will be lowered despite regular drenching. There is a lot of value in setting up a grazing plan to reduce the level of pasture contamination accumulation. The options for doing this will vary from farm to farm but will include such interchanges as:

Weaning lambs onto cattle grazing areas

Grazing weaner calves on lambing areas

Using summer crops to create a gap in the contamination/exposure cycle

Share the summer grazing areas of weaner calves with yearling cattle or older cattle

Share the summer grazing areas of lambs with ewes

Planning grazing shifts in March to move lambs or calves off areas that they have contaminated since the late spring

The first of these is so that the lambs and calves start off on a low level of contamination. Care must be taken with these options to not directly drench the animals directly onto these “clean” areas to avoid introducing only resistant worm eggs. See Drench Planning below. Crops, although largely worm free, do not share the same risk because any introduced worm eggs will struggle to complete their free living cycle.

Using older stock classes to dilute the accumulation of contamination on pastures can give live weight gain boosts. They will also reduce the selection for resistant worms as long as those older stock classes are not drenched.

Shifting young stock away from areas that they have contaminated requires careful planning and will need to take into account the worm species likely to be prominent and the relative lowered level of contamination on other areas, as well as the feed requirements of the stock.

Remember, the best tool for managing worms is feeding. Regardless of age, well-fed animals accumulate fewer worms and the worms have less impact.

Drench planning

There are three goals to keep in mind when planning drench inputs over the summer

1. Is the drench intended to be used effective?

Drench testing results (see page 1) should give all the information needed to choose an effective combination drench. This must be done early in the lamb drenching season.

Latest NZ science tells us that combination drenches given orally in cattle are the most effective. Other methods of administration are less likely to be fully effective.

2. The level of drench input matches the level of worm challenge.

Lambs or calves finished on pasture which has been spelled are likely to have a low worm challenge and therefore a need for less frequent drenching . On the other hand, if these animals go onto contaminated grazing, such as recently used lambing areas or longstanding summer weaner grazing areas for the weaner calves, then regular drench inputs are likely to be necessary. The expectation of the necessary drench frequency should be created at the start of the season. If the expectation is that drench intervals can be extended, it pays to put some faecal egg count monitoring in place at four weeks post drench to confirm that cleaner status.

3. Drench inputs are planned to select least for resistant worms.

When l ambs or calves go onto low contamination grazing (often called “clean” but it is seldom so) it is important not to load up this grazing area solely with eggs surviving the drench that they were given.

These areas can be protected by either:

Leaving some animals not drenched (3% to 10%), or

Waiting a few days between drenching and transfer onto “clean“ pasture, by keeping the animals on contaminated pasture before transferring them area, or

Grazing the area with undrenched ewes at a later stage (sheep only).

Once animals are on “clean” areas, it is very important to drench only when the need arises. Lambs or calves on contaminated grazing may need to be drenched at regular intervals to maximise weight gain.

While regular drenching can aggressively select for drench resistant worms, the risk of this can be reduced by leaving some animals not drenched at each drenching episode. If a fully effective combination drench is being used the percentage that need to be left is about 3%. Care must be taken when doing this if Barbers Pole is threatening. Selecting those not to drench as being the biggest is the easiest way, but if they can be selected based on their superior live weight gain there will be minimal overall production cost. Alternatively, grazing mature stock of the same species on the same area following the younger the stock will reduce the risk.

Planning and monitoring are the still the best tools to put in place “best practice”. Invest in the process.

More information

A Handbook of Sustainable Worm Management for Livestock Farmers

is freely available to all New Zealand farmers via free phone 0800 233 352. Alternatively request a copy from your local Beef + Lamb New Zealand extension manager or visit



This newsletter was written by Wormwise National Spokesperson Trevor Cook. He can be contacted on mobile 027 446 3616 or email