Drench Resistance in Cattle

April 2012

Research into the cost of the growing resistance of parasites to drenches

A look at drench resistance in cattle, and the Beef+Lamb funded research looking to measure the economic cost of that resistance.

Previous research has shown that anthelmintic resistance in cattle is common in New Zealand.

This is a trial commissioned by Beef+Lamb to look at the economic impact of cooperia (an intestinal worm) in cattle. It follows other trials commissioned by Meat & Wool (Beef+Lamb’s predecessor) in 2000 and more general resistance trial work in cattle.

There has been considerable debate amongst experts about the role that the intestinal worm Cooperia oncopheria plays in limiting beef production.

It is generally acknowledged that Cooperia worms are not as well controlled by pour-ons, compared with the control gained from other drench applications.

Resistance to ivermectin-type anthelmintics is said to be common and in cattle operations, levamisole drenches are the best means of controlling Cooperia.

It has been suggested that the Cooperia challenge on some bull-beef finishing systems could render them unsustainable in the future.

While that may be overstating things, one of the ideas behind the trial has been to try and quantify the impacts of resistance in terms of production.

Results from national survey suggest there is an overwhelming majority of farms with Ivemectin resistant Cooperia. (In 92% of the farms surveyed ivermectin failed to effectively reduce parasite egg counts).

The problem for farmers is that using an ‘ineffective’ drench will select for resistance, and sustained use of ‘ineffective’ drenches has led to high numbers of drug-resistant Cooperia on many NZ beef farms.

The Cooperia parasite is unlikely to kill cattle, but can be a production cost in cattle under 18 months of age. It can (with high levels of infection), cause scouring and slows growth rates in the first autumn/winter in young cattle.

In earlier trials resistance to cooperia was shown to have no measurable impact on spring growth in older cattle .

This trial is focused on young cattle. They are in eight mobs of 10 R1 cattle on the Flock House farm. Four mobs receive Eprinex pour on (Eprinomectin) only and four mobs get Eprinex plus Arrest C (Albendazole and Levamisole). FEC samples are being taken, condition scores, weights, fecal cultures and pasture larval samples etc.