Drug resistant worms threaten flocks

RED DEER — The lowly worm could be the biggest threat to the world’s livestock industry.

Internal parasites are a major problem for small ruminants such as sheep because of widespread resistance to commonly used de-wormers.

Anthelmintic resistant worms developed because of over-reliance on and misuse use of these drugs, said a sheep and goat specialist from the University of Maryland.

“Every time we expose that worm to a drug, we are on the road to resistance. It is inevitable,” Susan Schoenian said at the Alberta Sheep Breeders Symposium, which was held in Red Deer Oct. 16-17.

Sheep on pasture are more at risk because they can pick up all kinds of larvae residing in the first couple inches of grass. There are few problems for those in confinement.

She advises pasture rest and rotation when managing parasites. It takes about 60 days of rest for a highly contaminated pasture to recover.

Some farms are experiencing total anathematic failure because the worms can fight off every drug whether the farmers are treating horses or sheep.

Worms are showing resistance to all three classes of dewormers because they use the same mode of action.

Researchers are looking for breeding animals that are resistant to parasites, which will hopefully pass the trait to their offspring. Producers should consider culling animals that need to be dewormed frequently or those with high fecal egg counts.

Fecal egg counts that assess parasite loads need to be done before treatment. Manure should be re-checked 14 days after treatment. Producers should take samples from an animal that has not been treated for comparison purposes.

Researchers know that parasites can cause reduced wool and milk production, poor weight gain and reduced feeding efficiency. They can also affect immunity to other diseases such as pneumonia.

Veterinarian Kathy Parker said treatment use is restricted in Canada. Ivermectin is allowed only as a drench or injectable treatment. It also needs to be stored properly because it is light sensitive and could lose its efficacy.

Safeguard may be used off label with prescription from a veterinarian.

For more information, visit www.sheepandgoat.com.

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