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Beware The Bad Old Days Of Cruel Ostertagia

February 2, 2006

Beware The Bad Old Days Of Cruel Ostertagia Outbreaks

“Funny you should mention that,” says long-time Wanganui veterinarian John Pickering when asked if he recalls cases of costly and hard-hitting infection by the parasite Ostertagia. “We’ve just had two classic cases”

A Type 2 Ostertagia infection of “thousands” of Ostertagia worms saw a healthy pedigree heifer die within seven days.

Two heifers had suffered “classical” symptoms of Ostertagia, enduring severe scouring - “and one just went down and died”.

Rapid treatment of the second ill animal and the other 118 in the herd with an endectocide ended the problem.

The farmer had been using levamisole to cut costs and wasn’t aware he had a problem, says Pickering, who’s been practising for 30 years, 27 of them in Wanganui. “I don’t think a lot of a farmers around these days would know what Ostertagia is. The newer (endectocide) drenches have controlled it quite well.”

And even if the farmer had tested faeces for Ostertagia eggs in autumn, it would not have revealed the presence of Type 2 Ostertagiosis. The larvae are dormant in mucosa in the animal’s gut, awaiting the warmer conditions of spring before emerging as adults and laying eggs.

In the latest case, adult worms had emerged in “the thousands” according to the autopsy report.

The cost of losing the one heifer alone is estimated at $1300 because of its pre-ostertagia condition and pedigree.

“And that doesn’t count the sub clinical costs (of the Ostertagia outbreak), like how much was if affecting weight, growth rates and longer term production?,” Pickering says.

The case illustrates a potentially costly side effect of drench resistance and selection, according to animal health care company Merial.

The only partly-released findings of a national drench resistance survey could create a focus on killing a parasite, Cooperia, which least affects production – while allowing another more costly and cruel one, Ostertagia, to avoid treatment.

Reports on the survey say ivermectin is less than 95% effective against Cooperia on 92% of the 65 beef farms tested nationally, while levamisole is still reasonably effective against Cooperia.

However, reports on the survey say drench resistance, in tackling the potentially big production-limiting parasite Ostertagia, is not a major issue at present.

Merial’s Veterinary Technical Services Manager, Justin Hurst, says this indicates farmers need to put the survey into context on their own farms.

“If they use levamisole against Cooperia and quit the modern endectocide drenches, like Eprinex, they could see huge production and welfare costs due to Ostertagia unless significant management and monitoring changes are made,” Hurst says.

“Ostertagia has been so well controlled with endectocides since the 1980s, it’s not top of mind. And the larvae are poorly controlled by levamisole.”

Pickering says decisions on how to manage to reduce the chance of drench resistance developing, while still maintaining good control over production-limiting parasites, is a “tricky one” for many farmers.

While the country awaits the full resistance survey report, and a subsequent suggested strategy to manage resistance, Pickering’s view is farmers should keep checking to make sure a drench is effective.

“Very few farmers would know the (parasite) status of their farms,” he says.

“I’d be inclined to test and use appropriate drenches – and make sure the drenching is effective.”

In the recent Ostertagia cases, of course, the testing in autumn would not have revealed the inhibited larvae - lurking in the mucosa until spring. Using a quality endectocide with well researched claims against inhibited Ostertagia larvae is the key action to ensure peace of mind.

While many may be confused by the partial release of resistance survey information, Merial says farmers can use best practice guidelines for using anthelmintic drench in cattle. The company says it is publishing its guidelines to rural media and on its web site.
Release Ends


Ostertagia an enemy even in 1899

One of the earliest published reports on diseases and death in New Zealand cattle refers to ostertagia.

According to research published by S A Bisset, AgResearch, Wallaceville, the earliest reports of parasite infection problems were published in the relatively new colony in 1895 and 1899 by the chief veterinary officer of the New Zealand Department of Agriculture, division of veterinary science.

Gilruth reported that parasitic infection of calves in dairying districts was a frequent problem.

In 1899 he reported a recurring problem of calves dying on Southland dairy farms.

Bisset says: “Postmortem examination of an infected animal revealed the abomasum contained approximately forty thousand nematode parasites, which he tentatively identified as Strongylus cervicornis. However, from his description of this case we can be almost certain that the species involved was in fact Ostertagia ostertagi.”

Bisset says that while it had been recognised for many years “unthriftiness and even death” of young cattle were often associated with large nematode parasite burdens, the extent of production losses were not fully appreciated until the field trials of broad spectrum anthelmintics were carried out in the 1960s.

Drenching cattle: A best practice guide while the resistance debate roars on.

Animal health care company Merial says worms, like weather and exchange rates, are a commercial hazard which New Zealand farmers are capable of managing in the interests of their animals’ welfare, productivity - and their businesses’ sustainability.

While many may be confused by the partial release of national drench resistance study information, Merial says farmers could benefit from its best practice guidelines for using anthelmintic drench in cattle.

1. Determine the risks to:

2. Select management options relative to:
Actual and perceived risks
Measured performance
Animal handling options

3. For cattle less than ~300kg or 15 months ensure-
1. Maximum Ostertagia control
2. Broad spectrum worm control
3. Management of:
- BZ & Levamisole resistant Ostertagia &
- ML resistant Cooperia
Reducing drench dependency &/OR
Combining high efficacy products


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