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  • Writer's pictureWayne

Aiming for 12 months of zero worm eggs

Updated: Sep 29, 2020

Intestinal worms in sheep are nematodes and can cause major growth losses and death in sheep. Having come from a non-sheep background, I question everything to do with sheep.

There are “recommendations” from research that don’t make sense to me. To cut to the chase, it does not make sense to want to have worms in sheep. The current research wants refugia paddocks, which is where sheep can reinfect themselves with worms that have not been exposed to a recent drench.

We farm in a high rainfall area. We have some green pasture all year, so the environment is conducive for worms to thrive and cause havoc. And because we are at a high stocking rate and heading as high as we can as quickly as we can, we don’t have paddocks that are free of sheep for months to reduce the worm burden.

I come from 30+ years of agronomy with crops and pastures. It is a crazy idea to want herbicide susceptible ryegrass to be allowed to be in your paddock based on the erroneous idea of wanting it to cross pollinate with herbicide resistant ryegrass so that you have less resistant ryegrass.

You’d still have ryegrass causing yield losses!

It is a silly idea to suffer crop loss by allowing susceptible ryegrass to cross pollinate with herbicide tolerant ryegrass so that you can spray a herbicide to kill them all. It does not work like that.

To me it is the same with worms in sheep. The current recommendations are not to have zero worms. It is to have some that are diluting the resistant population so that the only worms alive are not the resistant ones.

It is true that every drench to control worms will kill the most sensitive ones and risk leaving alive the most resistant ones. The fear of the researchers is that you will go bankrupt because you only have resistant worms left unless you allow susceptible worms to be present.

We know from ryegrass that it is a numbers game. You should never rely on just one mode of action to control ryegrass. In fact, it is the same principle for everything in agriculture. You should never control a pest or weed with the same mode of action over and over. If you did, then you will select for those that can tolerate that mode of action and that mode of action will then not work. Obviously.

And then when I’ve asked experts what happens to a sheep when it never has a worm problem in its life, they warn me of impending disaster because the sheep will never develop adulthood tolerance to some worms, and so when it is exposed to worms, it will be very susceptible and suffer very quickly.

However, they missed my question. What happens to a sheep if it “never” has a worm problem? The answer is obvious that it would be a much healthier sheep.

The question then is, is it possible to have a sheep go through its life without worm problems? Today that is definitely possible.

I will side track for a minute. Using the current recommendations for worm management, you will always be putting worms back onto the paddock so that you keep having a problem. You are guaranteeing that you have to keep spending money, and at times losing production when worm numbers are increasing to the point where you need to hurry up and drench again. Usually some sheep will be lost.

I am finding myself disagreeing with the advice for worm management in sheep. It works well enough in dry areas where for half of the year, worms will die off every day (hot and dry). One timely drench coming into summer and then putting stock onto paddocks that have not seen a sheep for 8+ month when summer is very hot and dry will work. However, it does not work in our situation where we are green all year.

I am recommended to test poo samples regularly and do not drench until the numbers are past a threshold. This is not right to me. It guarantees we will have a problem.

As you may have read in earlier blogs, we have infested our paddocks after a mistake of listening to an agent that I did not need to quarantine drench trade sheep that were bought onto our property last year. Never again. No matter what, all sheep coming onto the property will be quarantine drenched and put into a gravel pit with feed for 1-2 weeks before going out onto the paddocks.

So, this is our strategy going forward. While I will be constantly introducing genetics that are resistant to worms on our farms, I want to go for a year with zero worm numbers. With no worm eggs going back onto the pastures, nature will day by day be knocking off the worms that are already on the pastures.

In nature, everything is eaten by something. There are organisms that will eat intestinal worms, and of course time will kill them, as will hot dry weather.

We have done some trials and know that we can keep sheep at near zero worm burdens. As it is with controlling ryegrass, it needs to be a multi-pronged attack on the worms. Sheep genetics is one - introducing rams with worm resistance, and culling every ewe lamb before she breeds that shows any sign of worm susceptibility. On our farm, all wethers are sold as lambs as we are a pure meat farm. We do not grow wool.

Where possible, grazing management helps reduce worm problems. Rotational grazing will increase the time before sheep come back to a paddock, and not only will there be more higher quality pasture to graze than set stocking, there will be less worms waiting for them.

When pasture is taller, less worms are consumed because they only climb up a few centimetres on grass. When pastures are grazed close to the ground, then the worms are consumed in larger numbers.

Today, we also have several good options with drenches with different modes of action. My view is that even if we have worms that, for example, moxidectin only controls 50% of the worm population, that means other modes of action only have half the worm numbers to work on.

If one of those chemistries controls 98% of the worms, then that only leaves 1% of the original worm population for another mode of action to work on.

So, we will continue monitoring worm eggs in the sheep poo, but to achieve our aim of zero worms returning to the paddocks for at least a year, we have implemented a long acting moxidectin injection to all our ewes, and giving them a drench like Q-Drench (it has four modes of actions in it). Moxidectin alone is failing on our property.

Then 4-6 weeks later, we drench them with something like Startect - remember the long acting moxidectin is still working for at least three months. Then 4-6 weeks later, we drench with Zolvix Plus (two modes of action but one is the same as the moxidectin).

Then a month later, they get another long acting moxidectin injection + Q-Drench + Startect. And so on never letting the worms to rebuild in the sheep and always having multiple chemistries in the sheep working on the worms and changing those modes of action every time we drench.

If we keep having zero eggs to say 6-weeks between each drenching, then we will extend the period without treatment, but not until we have gone most of the year with zero eggs going back onto the paddocks.

The lower the number of eggs on the ground, the less there is for the chemistries to control, the bigger the percentage that can be controlled by the environment, and the bigger impact there will be from organisms that eat the worms. And then as time goes on and we have better and better genetics with resistance to the worms, then we can lengthen the period between drenching.

However, I never want to allow worm numbers to build up before we drench. It is a numbers game.

Remember we do not create resistance genes. They are already there. All we do by using any control measure is to kill the susceptible and leave the resistant genes alive. So if you have 100 million worms and apply a drench, you are far more likely to find a resistant worm than if you only had 50 worms.

It is much easier to stop a car doing 10km/hr than 100km/hr. Worm control is a numbers game just like it is with ryegrass control.

We started this farm with peoples culled sheep, unfortunately, due to not having enough funds at the beginning to buy lots of top quality ewes. We are still building our numbers up as quickly as possible, but have just culled ~500 of our worst ewes and now we step up our culling pressure on any animal that scours, and we are on the hunt for better rams with worm resistance.

So, if you know of, or are a breeder of Ultrawhite rams or other 100% shedding sheep who measures worm resistance, please make contact with me via

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