Tool 11.8 Management of worms
Worm control programs are an important part of farm management on most sheep properties. Each state has detailed worm control programs designed to manage worms to minimise production losses and delay drench resistance. A great way to educate yourself is to look up WormBoss.
WormBoss is part of Australia’s premier parasite education hub, ParaBoss. Here you can find information on common worms, what worms are important to your area and when.
Two broad programs encompass the winter rainfall regions where Teladorsagia circumcincta (brown stomach worm), Haemonchus contortus (barber’s pole worm) and Trichostrongylus spp. (black scour worm) are the important worm species present; and the summer rainfall regions where barber’s pole worm is the dominant worm type. Local variations in climate and management make a significant difference to worm control. Seek advice from a veterinarian or animal health advisor to design a program specific for your property. A good program is flexible enough to accommodate climatic and seasonal fluctuations.
Winter and non-seasonal rainfall regions of southern Australia
Strategic drenching: time drenching to minimise drench frequency
A ‘strategic drench’ is a scheduled treatment that forms part of a proactive plan to reduce the contamination of pastures with worm larvae.
A ‘tactical drench’ is a treatment done in response to animal condition or signs of worms, e.g., scouring, weight loss or worm egg counts.
Strategic summer drench
Either one or two summer drenches can be given. These drenches help suppress the number of worm larvae on pasture for the rest of the year. The downside of summer drenching is that it contributes to drench resistance. For this reason, give the first drench when pastures dry out, but before late December, regardless of region. Prior to drenching, monitor worm egg count (WEC), as drenching may not be required if worm egg counts are low. Also, monitor WECs of all mobs to see if a second drench is required in February.
On annual pastures in Western Australia, ewes should not be routinely drenched in summer. Do a worm egg count in March/April to determine the need to drench, as egg counts often rise in late summer. Read the WA Department of Primary Industries and Regional Development information on Sheep worms: summer-autumn worm control or visit WormBoss for specific advice (see also signposts in Chapter 11.2 and Chapter 11.3).
The other ‘recommended strategic drench’ is the weaning drench for lambs. Drench and wean lambs no later than 14 weeks after the start of lambing. In some circumstances meat breed lambs benefit from staying on the ewes slightly longer but all lambs will benefit from drenching at this time.
It is normally not necessary to drench at lamb marking if ewes are lactating well and lambs are weaned no later than 14 weeks from the start of lambing.
If you routinely need to drench at lamb marking, consider:
- shortening the joining interval to 5 weeks, so that all lambs are marked at 2-8 weeks of age;
- preparing lambing paddocks with low worm burden by spelling, grazing with cattle, smart grazing, cultivation or haymaking;
- effective drench for ewes pre-lambing to reduce the amount of worm eggs shed onto the lambing paddocks; and
- using condition score of ewes to ensure they are in optimal condition for lactation.
Pre-lambing drench for ewes
Ewes lose immunity to worms around 3 weeks prior to lambing and then for the first 2 months of lactation. Because of this, small worm burdens in pre-lambing ewes can turn into heavy burdens very quickly, particularly in twin-bearing ewes. This also causes heavy worm larva contamination of lambing paddocks that the lambs pick up. A pre-lambing drench is therefore often required in spring lambing flocks.
This is especially important if ewes are less than condition score 2.5 at lambing, have short available feed or are on heavily contaminated pasture. Pre-lambing drenching 3-4 weeks prior to the start lambing is optimal. This is also a good time to vaccinate ewes and shift them to a clean paddock.
WEC monitoring is useful to determine if drenching is necessary. Prime lamb ewes, where lambs may remain on ewes for more than 13 weeks, may benefit from pre-lamb drenching, partly to reduce pasture contamination for lambs.
Tactical drenching
Additional drenching should only be done on information provided by WEC monitoring or sheep condition. Ideally, adult sheep need only 1–2 drenches per year and weaners, 2–3 drenches per year, depending on the season, management and stocking density. Sheep producers exceeding this frequency should seek expert advice.
Worm egg count (WEC) monitoring
WEC monitoring is done to decide on non-strategic drenching and summer drenching. Monitoring is also carried out before and after drenching to check on drench efficacy.
Grazing management
The aim of grazing management is to provide young sheep that are most vulnerable to worms with the pastures with lowest contamination. If possible, prepare weaning paddocks by grazing with cattle for at least 6 months, or with smart grazing. Alternatively, use wethers to prepare weaning areas for at least six months before lambs are weaned. Ideally, graze weaners on a second ‘safe’ paddock the following winter. Intensive grazing rotations will not necessarily reduce contamination with brown stomach worm or black scour worm. Visit https://wormboss.com.au/tests-tools/preparing-low-worm-risk-paddocks/ for information on preparing low-risk worm paddocks in your region.
Selecting sheep with low worm egg count (WEC) and low dag score
Research shows that long-term selection for sheep with low WECs (formerly called faecal egg counts) can reduce pasture contamination and drench frequency. Integrate with selection for all important wool and meat traits. Selection should also be targeted at reducing dag score as selection for low WEC can be associated with increased dags, so it is important to select for both.
Nutritional management
Research shows that sheep with good nutrition manage worm burdens better. Supplementation with a high protein grain or pellet has best impact. Maintain sheep at condition score targets and introduce rations slowly to avoid acidosis.
Timing of management events and systems
Spring lambing is an important driver of profitability in winter rainfall regions. Generally, late winter–spring lambing flocks have better worm control because ewes have better nutrition during lambing, although weaners have a higher risk in their first winter because they have not been exposed to many worms as a lamb. Wean lambs no later than 14 weeks after the start lambing onto a low-risk paddock. When considering flock structure, wethers are an important management tool to control worms, especially if no cattle are run on the property.
Summer or non-seasonal rainfall regions where barber’s pole is the major worm
The program will vary between season, drench resistance status and grazing management. Monitoring WECs is critical to determine when drenching is required. Both barber’s pole and scour worms need to be considered.
Control of barber’s pole worm
The program required will depend on resistance status. The barber’s pole season usually starts in October and extends to April on the tablelands, but heavy infestations can occur at any time of year. Time the first drench for late October to coincide with new infective larvae becoming available on pasture. Additional drenches may be required in late December and late February, or more often in warm wet seasons.
With resistance to certain drench actives widespread, it is essential to ensure you’re using an effective drench and performing regular WECs, both to monitor drench efficacy and to see if further drenches are required. Consult your veterinarian or animal health advisor to fine-tune plans appropriate for your property. Relying solely on long-acting products such as capsules or long-acting drenches will increase selection for drench resistance.
Long-acting treatments
Long-acting injectable moxidectin is often used to suppress worm numbers in sheep and subsequently larval contamination on pasture. Capsules are used less frequently in summer and non-seasonal rainfall regions but may also be used for the same reasons.
Due to established resistance, the protection period of long-acting injections is less than the label claim on most properties. This means that the products still work to suppress uptake of larvae but may or may not kill the adult worms already in the flock at the time of treatment.
See Tool 11.9 for more information on how to effectively use long-acting drenches to reduce the impact they have on drench resistance.
Primer drench
This is an effective drench that is given at the same time as the long-acting injection. Choose a product known to be effective (based on drench tests).
Exit drench or tail-cutter drench
This is another effective drench given to the flock around the end of the payout period of the long-acting injection. The timing of this treatment is determined by when the worm egg count of the flock rises. The best way to know when to administer this drench is to conduct worm egg counts at 30-, 60- and 90-days post-injection. These tests may be conducted at convenient management events such as before lamb marking or weaning.
Additional drenches
Additional drenches that may be required for broad-spectrum control of brown stomach worm and black scour worm include pre-lamb drenching (monitor) of ewes (see above) and a weaning drench for lambs no later than 14 weeks after the start of lambing. Additional drenches for lambs should always be based on worm tests over the following late autumn and winter.
Worm egg counts (WEC)
WEC monitoring is done to decide on tactical drenching and summer drenching. Monitoring is also carried out pre and post drenching to check on drench efficacy.
Selecting sheep with low WEC ASBVs
Research shows that long-term selection for sheep with low worm egg counts can reduce pasture contamination and drench frequency. Integrate selection pressure with selection for all important wool and meat traits. This strategy is most useful for control of barber’s pole worm.
Grazing management
The aim of grazing management is to provide young sheep that are most vulnerable to worms with the pastures with lowest contamination. Prepare weaning paddocks with cattle for 3-6 months (depending on time of year) or with smart grazing (see WormBoss). Alternatively, use wethers to prepare weaning areas for at least 6 months before lambs are weaned. Ideally, graze weaners on a second ‘safe’ paddock the following winter. Research indicates that barber’s pole worms can be controlled effectively by rotational grazing where the rotation length extends to at least 50 days. This is useful in summer when barber’s pole larvae survive for about 50 days. Visit WormBoss worm control program for sheep for information on preparing low-risk worm paddocks in your region.
Nutritional management
Sheep with good nutrition manage worm burdens better. Maintain sheep at condition score targets (see Tool 11.2). Research in the New England region indicates that protein supplementation on poor quality pasture can have a significant effect on worm control in lambing ewes.
Timing of management events and systems
Late winter–spring lambing flocks generally have better worm control because ewes have better nutrition during lambing, although weaners have a higher risk in their first summer because they have not been exposed to many worms as a lamb. Wean lambs no later than 14 weeks after the start of lambing, onto a low-risk paddock. When considering flock structure, wethers are an important management tool to control worms, especially if no cattle are run on the property.
Quarantine drenching
When purchasing sheep you are potentially buying in a worm problem, and it’s best to assume there is some level of resistance to drench in the purchased sheep and they should be quarantined:
- Utilising a quarantine drench means using a combination of no less than 4 unrelated drench groups. One of these groups should be a new drench active like monepantel or derquantel.
- If you have purchased sheep from high rainfall (more than 600 mm) or irrigation areas consider liver fluke treatment as well. For liver fluke distribution, see WormBoss liver fluke.
- After drenching, hold the sheep in quarantine in yards (small mobs) or a secure paddock (larger mobs) for 1–3 days (1 day if feed is green high quality, 3 if it is dry low quality) with adequate feed and water to allow worm eggs present at the time of drenching to pass out of the gut. If feasible, keep this paddock free of sheep, goats and alpacas for at least 3 months in summer or 6 months in cooler months.
- After quarantine, release the sheep onto a paddock that is likely to be contaminated with worm larvae due to grazing by other sheep. This would include most paddocks that have been grazed by home bred sheep for the last 3 months. This will ‘dilute’ the proportion of resistant worms surviving treatment with worm larvae already on your property.
- Do a WEC on the imported sheep 14 days after drenching for added confidence that treatment was successful.
- Get expert advice on up-to-date recommendations for quarantine treatments (especially if you can’t release the sheep into a paddock contaminated with home bred worms). These will evolve as the drench resistance picture changes.
Visit WormBoss How can drench-resistant worms be kept out of your property? for more information on keeping drench-resistant worms off your place.
