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Victoria worm, flies and lice update - April 2014

Hamilton: Andrew Whale, Livestock Logic (

Recent results

Variable seasonal conditions in the South West have caused tremendous variation in egg count results over the last 1–2 months. In some regions north of Hamilton, there has still not been significant autumn rain, and a lack of green grass is providing a nil worm risk for sheep, thus counts are staying very low. Contrasting to this, south of Hamilton there has been good autumn rain, and the country looks great, but we are seeing worm egg counts on the rise, particularly in young stock.

This highlights the need to consider your current season when assessing the likely risk of internal parasites on your property. As a general rule, when we have green grass, we have a good environment for worms to complete their lifecycle, so monitoring has to be more frequent, particularly in young stock. During dry times, provided we have drenched or monitored stock to ensure they have low worm burdens, they are unable to ingest infective worms from pasture to cause parasitism.

We have seen a number of cases of liver fluke causing mortality. All affected properties have had a history of grazing along creeks/streams that have had water flowing right through the summer. If you have ever had a history of fluke on your property or stock have been grazing near streams/swamps/creeks over summer, then we urge you to have a fluke test done by your parasite lab to ensure animals are not being affected by this parasite. It does require a different test to a normal egg count, so you need to ensure your lab conducts this test and you specifically ask for it. Undiagnosed fluke infestations can cause severe mortality and loss of production.

The following table reflects the amount of sheep that we have recommended a drench for at Livestock Logic in March to date.

Class of Sheep

% Requiring Drenching

Mixed Aged Sheep



Looking Forward

At this time of year, we get many questions regarding best options and requirements for ewes to receive a drench pre-lambing. The important factors to consider before drench selection (if required) is made are:

Current and previous worm egg counts for this mob and paddock

  • Reflects contamination level of paddock and current parasite level of sheep

Condition score of sheep and age

  • Ewes in better condition and >2years old are able to tolerate higher worm burdens

Nutrition for ewes over lambing period

  • Better nutrition of ewe enables her to resist worm parasitism

Time of lambing and how soon sheep can be yarded for lamb marking

  • The longer your lambing period, the higher the risk factor for a worm crash

Time since break of season

  • If season break occurred less than 4 weeks ago then worm egg count is not likely to reflect the amount of worms ewes have picked up since break of season. If season break more than 6 weeks ago, then a low egg count gives us good confidence that count will not dramatically escalate over coming weeks/months.

Consider the above for each mob of sheep pre-lambing to help you to determine your drench options. For those situations when most of the above create a higher worm risk, then your long acting products need to be considered, but when all are favourable, then we can have confidence a short acting drench (if at all) pre-lambing will be all that is necessary. The use of long acting products in dry autumns in sheep with a low worm burden is highly selective for drench resistance and a common theme that we find on properties with severe drench resistance.

If unsure of the right approach, seek some advice from industry consultants.


Benalla: Tricia Veale (

There was a good amount of rainfall in this area last month with a total of 78 mm. However, this month there has been a really good autumn break with 105 mm so far.

Some reports indicate that sheep are scouring badly. This has often been found to be due to the presence of moderate numbers of coccidian oocysts. Coccidia live inside the cells of the lining of the intestine. From within these cells they can produce thousands more coccidia that pass out with the dung. These are known as oocysts and are the resistant stage of the life cycle. They remain dormant on the paddock at this infective stage for some time, providing that weather conditions stay favourable. Winter frosts often do kill the oocysts but enough survive in sheltered spots to continue the cycle next spring.

Animals then eat the oocysts with grass and they pass down into the gut. The oocysts cell walls split open and very tiny tadpole-like sporozoites emerge. These can glide along the gut rapidly and they then enter the cells of the intestinal wall. Multiplication takes place in these cells, which eventually expand to the stage where they break open to release huge numbers of coccidia. The intestinal lining becomes irritated and inflamed. The animal’s body copes with this situation by sending down water to cool things off. This often results in scouring and diarrhoea. Young animals can become anaemic and suffer dehydration, weakness and loss of weight.

Coccidia infections are often self-limiting, they do resolve themselves. In the absence of re-infection only one cycle of development takes place. Under natural conditions however, repeated infections usually occur.

Young animals of all species are highly susceptible to coccidia, whereas adult sheep and cattle do develop a very good immunity to them.

Worm populations appear to be at moderate levels so it's good to check out what is happening on your place by getting a worm egg count done. Coccidian oocysts can also be identified during this test.

Some farmers have often said that they can tell if animals need drenching by looking at them. This is not quite accurate, and a worm test can save you hundreds of dollars if they don’t need drenching. Drenching unnecessarily can also contribute to drench resistance.

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