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Victoria worm update - April 2013

Tricia Veale, Benalla (

There was a moderate amount of rainfall in this area last month. However, this month it has been very dry with only 2 mm recorded so far. So farmers are saying that we need more rain.

Quite a number of the younger sheep are scouring badly. Very often, this has 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 which 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 seem 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.

Some farmers have 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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