Sheep parasite management

Internal parasites cause major health problems in Australian sheep. Managers must be vigilant when developing and implementing a control program to manage parasites in sheep. 

Internal parasite control needs an integrated approach, including:

• Effective use of drenches
• Grazing management
• Flock management (including early weaning)
• Breeding sheep more resistant to worms
• Nutrition
• Regular worm egg count monitoring (WormTest)

Let unchecked, internal parasites and intestinal worms in sheep can lead to significant production and financial losses. 

Most of the time, the signs and symptoms of worm infections aren’t obvious, but infected sheep will have lower productivity and performance.

High risk conditions for worms in sheep

Sheep producers should be aware of the increased health risks and diseases for sheep caused by ongoing wet weather. 

Worm risk is amplified by wet conditions and suitable temperatures that create ideal environments for egg hatching and larval survival on pastures. These same conditions make it difficult for graziers to create clean pastures for lambing ewes and weaners.

Prolonged rain events mean both sheep and producers have had to deal with a multitude of challenges including: 

• cold wet conditions increasing energy requirements
• degraded feed quality in standing dry feed
• high moisture content in short green feed
• minimal clover
• ideal conditions for worms to be picked up.

Be particularly vigilant for worms:

• Young sheep: May/June before severe winter weather
• Pre-lambing (include larval culture if barber’s pole worm was a problem last year)
• Prior to management activities (crutching, joining, shearing, weaning)
• At 6–8 week intervals after a drench

Worms for sheep producers to watch out for

• Roundworms (barber’s pole, small brown stomach worm, black scour worm)
• Flukes (liver and stomach flukes)
• Flatworms (tapeworms)

Barber’s pole worm is the most prevalent and destructive. Regular worm egg counts are essential to avoid ill health or death, especially from March to October and 4–6 weeks after significant rain that has follow-up rain (including the autumn break).

Worm tests

Worm testing identifies worm burden levels by counting worm eggs in faeces. Some laboratories can also perform a ‘larval culture’ (or larval differentiation) to identify worm types and proportions. 

Testing helps determine:

• whether sheep should be drenched
• which drench group to use
• when to conduct another WormTest

Drenching

Worms have 3 different life stages. 

1. The adult worms live in the sheep’s gut and lay eggs.
2. These worm eggs are passed out in the sheep’s dung.
3. They develop into larvae which live on the pasture, waiting to be ingested by a sheep where they can go on to develop into adults and repeat the cycle. 

Sheep drenches target worms living inside the sheep. Most drenches are short-acting, so there is no residual effect on new larvae that are ingested from the pasture.

If sheep return to the same paddock they after drenching, the larvae that they are exposed to will essentially be the same population of worms as previously. This population of larvae is called refugia, as they have not been affected by the drench.

If you move sheep to a new ‘clean’ paddock after drenching - for example, a rested crop stubble - the larvae that develop will most likely be from worms that survived the drench. These larvae are what eventually can go on to create drench-resistant worm burdens.

• Always use an effective drench
• Conduct a Drench Resistance Test (DrenchTest) to check resistance
• Use a drench with one effective ingredient rather than multiple ineffective ones
• Perform a DrenchCheck about 1 week after drenching; effectiveness requires >90% reduction in worm egg count

Managing drench resistance

• Avoid drenching if you don’t have to. This is especially important in dry or drought conditions. A WormTest can be used to help decide if drenching is warranted and should be done a few weeks out from your anticipated drenching time (i.e. pre-lambing, at weaning, or when scouring is noticed).
• If drenching is necessary, use an effective one. Ideally the drench should kill as close to 100 per cent of the worms as possible. A drench-resistance trial or a Drench Check can show you which drenches are most effective on your farm. This involves a WormTest before drenching and another 10-14 days after drenching to check that the number of worm eggs has significantly reduced.
• Follow drench label directions. Always drench to the heaviest sheep in the mob and make sure your drench gun is properly calibrated. We want to avoid underdosing.
• Use a combination drench. Using drenches with two or more active ingredients reduces the risk of drench-resistance developing. Worms that are resistant to one ingredient may still be killed by one of the other ingredients. The likelihood of a worm being resistant to multiple drench groups is much lower than to an individual drench alone.
• Avoid drenching straight onto specifically prepared low-worm-risk paddocks. If you have to, treat the sheep with an effective drench from a different group when they leave the low-worm-risk paddocks. You could also ensure that next time, the paddock is grazed with a different mob of worm-carrying sheep that were last treated with a different drench then the first. The aim here is to ensure that the worm larvae that end up on the pasture aren’t just the ones that are resistant to the drench used on the original mob.
• When quarantine drenching newly purchased sheep, including rams, use a drench that contains four unrelated drench groups, including one of the new drench groups. One to three days after treatment, when the worm eggs present during drenching have passed out, move the new sheep to a paddock that has had home-bred sheep on it. This ensures that larvae picked up are representative of the worm population on the property. If possible, avoid grazing the first quarantine area (where the eggs have been deposited) for three months in summer or six months in winter to give time for any larvae that did develop to die.

Contact your Local Land Services District Veterinarian on 1300 795 299 for advice.

Integrated worm control in sheep

When developing an effective worm control program for your farm it’s important not to rely on chemical drenches alone. Worm egg counts, age of livestock, stocking densities, nutrition, pasture management, use of chemical drenches and seasonal factors all need to be considered.

Effective grazing reduces chemical intervention and improves nutrition. Sheep immunity (genetics and nutrition) also plays a role in worm resistance. Consider breeding sheep more resistant to worms.

An integrated approach includes:

• Strategic grazing to reduce paddock contamination
• Avoid set stocking in one paddock
• Divide paddocks for spelling or cross-grazing
• Prevent grazing in the “worm zone” by keeping pasture at least 5 cm high

Watch Worm control in livestock video

In this video, expert parasitologist, Dr Matt Playford, Dawbuts Pty Ltd, provides insights into common intestinal worms in sheep, goats and cattle plus practical tips to help you work through worm infections and control programs on your farm.

The production of this video was funded by the Early Needs Recovery Program.

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Video transcript

Worm control in livestock

Despite all the research and the progress that has taken place

over the last hundred years, we still hear so many stories

of really bad parasite problems in livestock across Australia

The cost of worms to the Australian sheep industry is $665 million

each year, as calculated by Meat and Livestock Australia

and the cost to the cattle producers is more than $100 million per year.

Now they’re economic figures, they don't really tell you

the other aspects.

The animal health aspects of worm infections that are affecting

our animals.

The biggest impact is really in productivity.

So most of the disease that we see due to worms isn't obvious.

We're not actually seeing outside signs

we're not seeing scours, we're not seeing anaemia.

But the animals ability to grow, produce wool, produce milk

and look after themselves is severely compromised.

When you're

seeing clinical signs of disease, the animal is so badly

compromised that it may take a long time for it to get better.

What we want to do

is be able to look over the horizon and pick up the early signs

before they become manifest as physical signs in the animals.

A lot of people look at their animals and think,

what sort of worms are in the animals?

And that's it, that's 100% of what they think about.

Whereas people who've got a bit more education about worm

control are looking at the animals, sure,

but they're also looking at the pastures and think, how can we best control

the worms on the pastures

to decrease the risk to animals before the worm problems even begin?

Looking back

in history, we have had worm control programmes that were essentially based

on the calendar and a lot of people are still doing this unfortunately.

Now, we have to rewrite this chapter.

So calendar based worm

control programmes you can pretty much say are gone.

And the reason is because a) they don't work very well

and b) they actually drive resistance very rapidly.

And so the less you actually drench,

the better outcome you're going to have for sustainability.

Now, of course, it's still necessary to drench on most properties,

but you really want to be

targeting the drenches for when they're going to have the most benefit.

So instead of having a trigger for drenching,

like ‘I noticed the animals were scouring’

or, ‘It's that time of year’

work out your own algorithm,

which is a combination of factors, animal factors, worm egg counts,

climatic factors, the amount of pressure on the pasture.

I'd start off by doing a worm egg count and finding out what

type of worms and what levels of worms there are in each mob

and then to back that up, you can start doing drench checks.

So each time you drench, you can do a worm egg count 14 days later,

and that way you'll know exactly how well that drench has worked.

Not overall, but against each individual species of worm that you've got

on the property and work out if there really is a need for drenching.

because if you can get away with not drenching and instead substitute

supplementation or change of paddock or some other way of getting animals through

without drenching, you'll decrease the amount of resistance.

About 15 years ago the Australian industries

started up the Worm Boss programme and that's now evolved into Paraboss

and that provides information for sheep, goat and cattle producers

about how to get best parasite control specific for their own farm.

The other thing that Worm Boss has

is directions for doing your own drench resistance test.

So I know that a lot of veterinarians will carry this out for you.

Some rural stores will do it.

The second thing, and this is probably very manageable for

for small producers is what's called targeted, selective treatment.

And targeted selective treatment means you go through a mob of sheep, for example,

and you decide which ones need a drench, which ones don't.

For example, 100 sheep in the race, you can actually assess them

by body condition score

by using change of weight maybe from an electronic ear tag.

And you can draught them and decide which sheep

you need to drench and which ones will be okay without a drench.

One feature of modern livestock production is it's

very intensive, it's high production, and that drives high stocking rates.

High stocking rates

are good for productivity up to a certain extent,

but they also drive high worm burden.

The critical thing for grazing ruminants is that they're not exposed

to huge numbers of worms on the pasture.

The easiest way of doing that is to use rotational grazing.

So you move the animals from one paddock to the other, which means that the paddock

that's become contaminated, we see an exponential decay curve.

We see all the worms decreasing at a predictable rate

depending on the temperature, and they eventually die out on that paddock

and then may not match your, you know, nutritional needs, the energy demands

of the animals, the agronomic requirements of the paddocks.

But it's an important consideration.

This is a perfect example of rotational grazing.

They're running 140 head of Wiltipolls on 25 acres.

What they have done is divide

the pastures, both using set fencing

and electric fencing, and they're able to keep the animals in good condition.

They've always got plenty of nutrition and with low worm burdens,

they both test and they only drench twice a year, which is pretty remarkable.

It's a great achievement.

The most important thing is the low contamination pastures.

And the second one is nutrition.

By improving nutrition, you're always going to

increase their ability to have immunity against worms.

For this part of Australia, southern New South Wales,

a constant threat is Barber’s Pole Worm for sheep and goats especially.

And it's a killer.

It will very rapidly kill large numbers of sheep and goats.

So that's something we need to be aware of, particularly

when we're having warm, wet weather, which has been a feature of

of the last five summers.

Another constant worm is Brown Stomach Worm

and Black Scour worms, and we call them together the scour worms.

They're the ones that cause dags and predispose animals to fly strike.

But they also are constantly nagging away at animals growth rates

and stopping them from getting to either sale condition

or body condition score for reproduction.

In cattle we've got the same worms there,

but we've also got another one called Cooperia.

That's a small intestinal worm,

and it's a constant problem because it breeds very quickly.

It's got a high reproductive rate and so most of cattle paddocks

contaminated with it, and that mostly affects growth rates of younger cattle.

We've been very fortunate in the last 30 years to have the best products

ever invented for cattle worms, and they're called the mectins.

We've had that for 30 years and we've just realised in the last few years

that those mectin products have started to fail.

They're not killing all the worms.

Now this is a big wake up call for us because a lot of producers are simply

just continuing to do the same things as they've done

for the last 30 years because they've had good results.

The first thing I'd urge cattle producers to do is test,

test to know when the animals need a drench

for starters, and also test

after the drench to check that that particular product is working.

In general, combination products are going to work

better than products that are only got one active ingredient.

General advice for sheep producers is to have a better understanding

of the worm lifecycle so that they can predict

when the worms are going to be bad.

Now, on top of that,

they can do regular monitoring, testing of their animals’ dung samples

to work out the worm egg counts, and also know what worm species are there.

And that'll give them an indication of whether the animals need extra feed

or change of paddock or maybe even need a drench.

In terms of set drenching

there's probably two times when you can justify set drenching.

The first one is a weaning drench, almost all lambs

have got a need for a drench when they're weaned.

Some people may not do that and good luck to them if they can get away with it

by looking at nutrition or putting lambs onto low worm burden pastures.

That's great.

The second one is a pre lambing drench and the reason for

this is because ewes prior to lambing have got huge metabolic demands

and particularly we're talking about ewes carrying twins.

In fact they can't eat enough to meet the energy demands

that they have from pregnancy and lactation.

And so it's very important that they are able to go into the last

little bit of pregnancy and lactation without any worms,

because there's this phenomenon called P.P.R.R.,

which many people are already familiar with:

Peri-Parturient Relaxation of Resistance,

which means that because the ewes are prioritising

reproduction and looking after their babies,

they're not prioritising immunity against worms.

And so the worm burdens increased dramatically,

and the worms that are inside them also lay more eggs.

And so you get terrible contamination of almost every lambing paddock.

Goats are a very different animal from from a sheep

and we can't just treat goats as sheep with a personality.

Goats have developed a physiology that's adapted to browsing

and they’re happiest when they're putting the head up

nibbling on trees, shrubs and getting their food far away from the ground.

And because of that, when we make them eat off the ground,

they pick up very large worm burdens, and that can often be fatal.

The best thing that people can do with goats is not just set stock them.

And this is very difficult on small farms, but rotating goats around paddocks

is a great way of offsetting

the worm burdens that they’re going to pick up.

Set stocking is very dangerous for goats.

Worm Boss is a really user friendly

way of learning about both things to solve your current problem

and also general education about worms and parasite control in livestock.

Local vets are also a fantastic resource.

They've got skills in diagnosis.

Local Land Services are a great local resource

because they understand local conditions and they're able to respond very quickly

to things that happen in a particular region.

I've been very blessed in my career

I've worked with a lot of farmers who've been really inspirational

and have contributed a lot to the quality of my life and also

worked with a lot of parasitologists who've done the same.

So it's great to be able to give back in some way,

but the challenges that they face a greater now than ever before.

We need to have a different focus for

worm control than we have in the last 30 years.

What we're trying to create is a robust industry.

We want every farm to be bullet-proof to actually have a high degree of resilience

so that if something bad happens, they can bounce back very quickly.

And not only that, they can predict the critical times,

have a contingency to ward off the high risk times.

Tips for monitoring sheep for worms

The key message in a wet season is that sheep require different management:

• Increased monitoring by faecal egg counts (FEC) (every 4 weeks) to understand what is happening in each mob
• Increasing drenching frequency if indicated by FEC
• Drenching of ewes may be required during lambing or at lamb marking
• Increased importance of drench resistance testing
• Increased importance of pasture management by spelling for longer, slashing, smart grazing or rotational grazing with alternate species

In some situations, where there is significant larval contamination of paddocks and no clean paddocks can be found, use of long acting anthelmintics (either injections or capsules) have been warranted. This has been required for worm control during lambing and in weaners on some properties.

Long-acting products do bring some risks, particularly accelerated resistance development and poor control if there is already resistance to that class of anthelmintic. The risk can be managed by using priming doses of short acting effective drenches at the time of treatment with a long-acting, use of faecal egg count monitoring of the effectiveness of control, and the use of another effective drench at the end of the expected duration of the long acting (so called tail cutter treatments).

Spelling of paddocks is a recognised method of decreasing the numbers of larvae on pasture. This approach can be difficult in a wet season given the favourable conditions for larval survival. Even in normal seasons it will take 4-5 months for larval number to decline during winter and spring (2-3 months in a “normal” summer). In a wet year, this period can be expected to be extended. An alternative is to alternate graze during this period with cattle.