Cattle grubs are an ever-present livestock pest, despite some evidence to the contrary, concluded a long-term study of Alberta cattle conducted by Dr. Doug Colwell, a livestock parasite researcher at the Lethbridge Research Centre.
Dr. Colwell’s results are contrary to other recent studies in Alberta, which found little evidence of cattle grubs at packing plants.
Those studies concluded the cattle grub battle–started in the early 1970s with mandatory application of control products to all classes of cattle–was essentially won.
But Dr. Colwell believes the conclusion may be founded on a somewhat narrow research design.
“The problem we see with those surveys is that they were looking for cattle grubs in the backs of animals at the packing plants,” he said.
“But 95 percent or more of cattle that go from a feedlot to a packing plant have been treated with a broad spectrum control product in the feedlot so low numbers of cattle grubs were observed.”
Dr. Colwell sees cattle grubs frequently in cattle on Alberta rangelands, particularly in calves as they come off grass in the fall.
“We see indications of a large amount of warble fly activity so just because the cattle grubs aren’t found in the packing plant doesn’t mean the animal was never infected with the parasite,” he noted.
To test for cattle grubs, Dr. Colwell analyzed blood samples for the presence of antibodies to cattle grubs. “We can tell if the animal has been infected at any time in its life–even if the parasites have been killed by a control product,” he said.
Four cattle herds at two different ranches in southern Alberta were studied over a 10-year period.
On the ranch with a long history of parasite control, between 8.8 and 73.3 percent of the calves tested positive for cattle grub antibodies.
Those results show that despite consistent therapeutic treatment for control of cattle grubs, re-infestation–most likely from populations outside the ranch–occurred annually.
What all this means for producers is that both cow/calf producers and feedlot operators should continue to keep cattle grubs in mind when planning their parasite control objectives.
Feedlots are doing a good job of treating for cattle grubs, evidenced by the absence of grubs at packing plants.
But there is evidence pointing to reduced weight gains in calves that have been infested, and there is indirect evidence cattle grubs have immunosuppressive effects on the calves, leaving them more susceptible to disease.
Treatment for grubs benefits calves by boosting their immune system and making them gain better.
Fort Frances Times
Local News from Across the Rainy River District
