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ParaBoss News - February 2021 - Feature Articles

Fast Fact – Brain burrowing hatchlings

Taenia solium, or the pork tapeworm, is a human tapeworm found globally, but more often in regions with poor sanitation. Pigs become infected by ingesting eggs found in human faeces, which then hatch, resulting in larvae burrowing into the pigs’ intestinal wall and going on to form cysts in the muscle. Humans become infected by eating raw or undercooked pork containing larval cysts, which develop into a tapeworm head and attach to the small intestine. Infection with T. solium often presents with few or no symptoms, and many infected people may not know they have a tapeworm. However, when a person ingests eggs found in the faeces of an infected person, the hatching eggs can burrow into human brain, muscle and other tissues, much as they do in pigs. These then form larval cysts which result in cysticercosis, a disease which is linked to seizures.

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Feature Articles

Stopping resistant worms at the farm gate

Drench resistance is a big problem for producers, as increasing populations of resistant worms limit the effectiveness of drenches. Developing resistance is usually a gradual process, as successive generations of resistant worms survive drenching and go on to reproduce, eventually becoming the dominant population of worms on a property. Each property will have varying degrees of drench resistance, based on the history of drenches used within the flock.

If you’re restocking or planning to restock, it’s safest to assume that any sheep you introduce to your property are carrying some amount of drench resistant worms, as resistance will be present wherever drenches are used. This means new sheep can add to the overall drench resistance seen on the property, by providing a pathway for worms resistant to one or more chemical actives to contaminate pastures and infect the existing flock.

One way to manage the issue is through what’s known as a ‘quarantine’ drench. Holding sheep in suitable yards or small paddock gives an opportunity to conduct a thorough drench involving at least four unrelated actives, including the newest actives to hit the market (which are most likely to  provide the least resistance). The combination of several actives aims to kill all worms present in the sheep. Then, while ensuring they have adequate feed and water, keep them in the yard for at least three days, thus allowing any remaining worm eggs present at the time of the drench to pass out of the gut, before releasing the sheep onto the property.

Release the sheep onto another paddock that is already contaminated with worm eggs, to dilute any possible remaining eggs from the introduced sheep, and conduct a WormTest after 14 days to ensure the treatment was successful. If the treatment was not successful, seek professional advice.

Lastly, keep both the quarantine paddock and the interim paddock free of livestock to allow any worm eggs deposited there to die, which will take between 3–6 months depending on the season and the weather conditions — typically the hotter and drier, the faster this will happen.

Find out more about quarantine drenching via

Tackling the source of a lice infestation

A lice infestation can take up to six months to show obvious signs on-farm; by the time you’re seeing lice, it can be hard to figure out exactly where those lice have come from. Our January edition of ParaBoss News spoke about considering all introduced sheep to be lousy, and treating them accordingly. While newly purchased sheep are certainly a common pathway for introduced lice, there are a few other means by which an infestation may begin.

Most significant among these is straying sheep — be they yours or a neighbour’s — to which the obvious solution is sound, stock-proof fencing. When fences are poor quality, and neighbouring properties are infested, it’s no big leap that any straying sheep may come back to your flock with a lice problem. Of course, fencing can be time-consuming and expensive, so if you’ve found your fences to be a potential lice risk, make sure to weigh it against the ongoing cost of treating infestations.

Another factor to consider is your shearing practices. Split shearings, wherein different mobs on the property are shorn at different times, leaves a reservoir of lice in some sheep on the property that can then spread back to shorn and treated sheep later. At a minimum, where lice are known to be a problem, keeping different mobs separate, limits the chances that lice can spread. Think about moving to a single shearing, combined with post-shearing treatments to eradicate lice completely. Consider the biosecurity implications of your shearers, too, as lice have been shown to survive more than a week on moccasins and could thus move between properties when the shearer does. This is best addressed by asking shearers to change clothing and footwear if they’ve been on a property with lousy sheep.

Find out more about sheep lice biosecurity and effective treatments via

Selecting rams and ewes to reduce flystrike risks

It’s been a wet summer for parts of eastern and southern Australia, and with that warm, wet weather has come a greater flystrike risk. Many of our correspondents in our State Outlooks newsletter have raised concerns over the significant flystrike risk this season, going back to late spring. If you’ve experienced a bad season for flystrike, the upcoming reprieve may be an opportunity to revisit your flystrike management and consider breeding for resistance.

Breeding for resistance is a long-term strategy which, over time, will reduce the susceptibility of individual sheep and therefore decrease the number of high-risk sheep within the flock overall. For commercial breeders, there are four key steps to breeding a flystrike resistant flock.

Firstly, select rams from a reputable breeder who provides Australian Sheep Breeding Values (ABSVs) for wrinkle, dag and breech cover, and choose rams which have the lowest value (and therefore greatest resistance), balanced against other performance measures. Next, assess your ewes for those same traits (as well as fleece rot), and either cull higher-risk ewes or eliminate them from your breeding program. Join your best ewes to your selected rams for the best chance of producing lambs with the desired traits. Lastly, assess your lambs for flystrike risk and decide on their flystrike management going forward, including whether they’ll remain in your breeding program.

By following a rigorous selection approach which puts downward pressure on flystrike risk, you can reduce your reliance on chemical treatments and other management strategies and begin seeing results over only a handful of generations.

Find out more about breeding to reduce flystrike susceptibility via

Knowing when and how to use a long-acting drench for your goats

While short-acting drenches kill worms when administered, long-acting or persistent drenches can provide a further period of protection wherein ingested larvae are also killed. At high worm-risk times, this may be desirable as it prevents worm burdens from building up and putting the animal at risk. However, the effectiveness of long-acting treatments must be balanced against their greater risk of accelerating drench resistance in worms. This happens because the worms are exposed to the chemical active over a longer period of time, which means there are more opportunities for resistant worms to survive and reproduce, while the diminishing effectiveness of the active toward the end of the protection period increases selection pressure in favour of partly resistant worms.

When administering a long-acting or persistent product, there are a few techniques which can increase its effectiveness and slow the rate of drench resistance forming. These include primers and exit drenches, both of which are a short-acting treatment with the primer given concurrently with the persistent treatment and the exit drench (or tail cutter) given near the end of the persistent treatment’s activity.

The primer drench should use highly effective actives, different to the persistent product (ideally a combination), to kill adult worms that are resistant to the long-acting drench. In the case of a mid-length treatment, a primer is advisable, but may not be cost-effective.

An exit drench or tail cutter is given two weeks after the real protection period for a mid- or long-acting product ends (this may be earlier than the label claim if resistance is already present), which should kill any larvae which survived the persistent drench. An exit drench is also highly recommended for a mid-length treatment.

As there are far fewer products available for goat producers compared to sheep producers and dose rates for sheep are not necessarily suitable for goats, a consultation with your veterinarian is a legal requirement for off-label use and they will assist you to determine the best product to use, appropriate dose rates and withholding periods. If your goats produce milk for human consumption, also pay special attention to any product which is labelled as being unsuitable for dairy goats!

Find out more about using long-acting drenches via

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