Back to News Articles

ParaBoss News - December 2020 - Feature Articles

Fast Fact

Botfly can be a real bother

The human botfly (Dermatobia hominis) is native to Central and South America. Female botflies lay up to 50 eggs at a time on captured insects (mosquitos, flies or ticks), before releasing the insect to find a host to deposit the eggs on to. Once the eggs sense the body heat of the human host they hatch and attempt to crawl into the feeding site of the mosquito, or through hair follicles. Once under the host’s skin, the larvae have an incubation period of six to 12 weeks in which the botfly feeds. Dermatobia hominis larvae cause a raised lesion in the skin that becomes hard and sometimes painful. Cases have been reported where the hosts can feel the larvae moving when they shower or cover the wound. Mature larvae will exit the host, drop to the ground, and pupate in the environment. Adult botflies emerge approximately one month later and repeat the life cycle.

Share this newsletter

Know someone who might be interested in ParaBoss News? Forward this email to family, friends and coworkers, or have them subscribe at

ParaBoss on Facebook

Feature Articles

Drenching made easy with the WormBoss Drench Decision Guide

Is it time to drench your sheep? Many contributors to the November edition of State Outlooks suggested that it may be time for a strategic ‘summer’ drench for those in winter-rainfall regions. Determining whether or not a drench is required is based on a number of factors, including any signs of heavy worm burdens, the age of the sheep, and the weather conditions on the property. In some cases, WormTest might be required to assess the worm egg count before you make a decision.

The WormBoss Drench Decision Guides have been created to make your life easier, by helping to determine a way forward. The Guides include tailored advice for each of the WormBoss control program regions, accessible as either an online interactive tool or you can print it as a decision tree, both of which step you through your current situation with the mob to make a recommendation on if and how you should drench.

While they cannot replace specialist advice from your veterinarian, having a Drench Decision Guide handy can help make what can sometimes be a tricky decision much easier.

Find out more about the Drench Decision Guides.

Warm and wet weather increases flystrike risk

With the weather continuing to heat up as we enter summer, producers who have had their share of spring rain will likely be seeing a boom in fly numbers. Warm and wet weather is perfect for flies, and the risk of flystrike in these areas will be high.

Treating flystrike is essential, as struck sheep tend to attract more blowflies, endangering the rest of the mob and posing a significant welfare risk to those sheep that are already struck. In brief, treat flystrike by shearing around the strike to remove struck wool, remove and kill all maggots from the wound, and apply a registered flystrike dressing to the shorn area to prevent re-strike.

Removing struck sheep from the mob and placing them in a ‘hospital’ paddock will reduce the risk to the rest of the mob and allow you to monitor their recovery. If you are breeding for flystrike resistance, ensure that you cull any struck sheep from your breeding program to improve your breeding efforts. If you don’t have a concerted breeding focus against flystrike yet, take the opportunity to look at those struck sheep and see what characteristics are driving strike on your property so that you can introduce focused selection pressure. Just one generation, using a much more resistant ram, can make a substantial difference to flystrike susceptibility in those progeny.

Find out more about treating flystruck sheep.

Single shearings and regular monitoring help eliminate lice

In the November edition of ParaBoss News, we explored quality fencing and biosecurity as means to keep lice from infesting your sheep flock. While this is an important strategy to keep lice out, it does not help those who are dealing with a lice issue already on their property.

Split shearings can make it difficult to fully eradicate lice, as some lice can survive and multiply on sheep that were not shorn most recently. This means as the fleece grows back, lice can transfer from sheep that are still lousy. Consider conducting single shearings until the lice are fully eradicated — but make sure your shearers are not bringing lice onto the property with them!

Once you make a start on eradicating lice, regular monitoring of sheep — at least twice a year for existing mobs — is vital to ensuring that you catch any developing issues early and have a chance to treat sheep before they begin to devalue the fleece or spread lice back to mobs from which you have successfully eradicated lice.

Find out more about monitoring for lice

Selecting the right drench for your goats

Worm control is all about selecting the most effective approach for your herd and property. Depending on your enterprise, a combination of non-chemical management and chemical treatments will be the most effective. Although this can be made more complicated due to the much smaller range of products registered for use in goats, when compared to sheep.

All sheep products are able to be used with goats, but legally only with a veterinary prescription because dose rates and withholding periods will not be the same as for sheep. Firstly, your vet will be able to advise you on the appropriate off-label dose rate for your goats (which will vary according to the products). Secondly, your vet will be able to guide you on which combinations are best suited to your region, because the worm types and extent of drench resistance varies across regions. Drench resistance is common in goat herds, as many drenches are used incorrectly as dosage rates differ between sheep and goats. By using a DrenchCheck you can see how effective your drench actives are; simply conduct a routine WormTest, followed by a drench (if indicated by the WEC), followed by another WormTest 14 days later, to assess the impact of the drench on worm egg counts.

Find out more about conducting a DrenchCheck.

Image: Berwyn Squire
Image: Berwyn Squire

Targeted Treatment drenching guidelines released for southern Australia

by Dr Brown Besier, Brown Besier Parasitology

“Targeted Treatment” involves drenching only a portion of specific mobs at very particular times to slow down the development of drench resistance across a property by having more of the worm population “in refugia”.

Extensive trialing in Australia has demonstrated this is a safe, easy, and proven technique for significantly slowing down the development of drench resistance in scour worm regions, but is not suitable where Haemonchus (barber’s pole worm) is a problem.

The following points are the basics, but if you are contemplating this strategy, read the entire article carefully, in particular, the guidelines at the end, and seek advice from a suitable animal health advisor should you have any questions.

  • Targeted Treatment suits winter rainfall regions where haemonchosis is not a routine occurrence.
  • Only use the strategy in adult sheep mobs (>2½ years of age) with average body condition score of 3.0 or more.
  • The best individuals to leave undrenched are those with a body condition score of 3.5 or more based on a visual check when in the race for drenching.
  • At least 10–20% of the mob should not be drenched if a benefit is to be gained, leaving a mean of 50 eggs per gram (or less) on average across the mob after treatment.
  • Monitor the mob that received a Targeted Treatment: check worm egg counts in autumn, or after 1–2 months at other times.

Read the full article

ParaBoss News is produced with support from
Animal Health Australia

For December 2020 state outlooks, please follow the links below:
Back to News Articles