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It's That Time of the Year: Deworming for a healthy herd

Dr. Vicky Lauer for Progressive Dairyman Published on 11 September 2017
Dairy cattle in pasture

Frequent rains this spring and summer have led to lush, fertile pastures. Grass isn’t the only thing that has flourished with the timely rains, though. Parasites reproduce more rapidly in warm, humid weather too, increasing the risk of economic loss.

Internal parasites are a significant problem in pastured cattle. Female worms lay eggs that are passed to the environment through the manure. The eggs hatch into larvae and then climb blades of grass while they are still wet with dew. Cattle ingest the larvae as they graze, and the parasites develop into adults to complete the life cycle.



Cattle on drylots or in confinement rarely battle internal parasites since grass contact is minimal to nonexistent. However, confinement cattle are more exposed to external parasites such as lice and mites, so a pour-on dewormer will be especially beneficial.

Roundworms are the most devastating group of internal parasites, infecting the abomasum (true stomach) or intestines. Some roundworms suck blood and cause anemia while others only damage the lining of the intestinal tract. Roundworms are becoming increasingly resistant to dewormers, making control more challenging.

All internal parasites rob nutrients from the animal, thus decreasing feed efficiency, growth rate and milk production if the animal is lactating. Weight loss, diarrhea, a “pot-bellied” appearance and a long, scraggly hair coat are the most obvious signs. Severe parasitism leads to fluid retention, especially under the jaw, brisket or abdomen. Parasites are easily diagnosed by a fecal flotation run by your veterinarian.

Young cattle are often the most seriously affected as they don’t have the fat reserves to cope with nutrient deprivation. Dewormers yield three to four times a return on investment due to increased growth rate and feed efficiency, which makes deworming pastured cattle one of the most cost-effective and beneficial decisions you can make.

There are many commercially available dewormers, several of which are effective on both internal and external parasites. Consult the dewormer label to see which specific parasites are targeted, and speak with your veterinarian to decide the best choice for your operation.  end mark


PHOTO: Dairy cattle in pasture. Staff photo.

Vicky Lauer
  • Vicky Lauer

  • Professional Services Veterinarian
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