Only 5 percent of parasites live in cattle, which means 95 percent of parasites are on pastures. That is why Dr. Bert Stromberg, parasitologist and professor, College of Veterinary Medicine, University of Minnesota, says a parasite control program also can help reduce parasite burdens on pastures.

Cattle are only one stop on the parasite life cycle; therefore, parasite control programs should focus on cattle and the resulting burden on pastures.

“We know that a large number of parasites live on the pastures and they can survive there for an extended period of time, even during Minnesota winters,” Dr. Stromberg says. “Therefore, producers should keep in mind that a strategic deworming program should focus on taking care of parasites in the host before they contaminate pastures.”

Dr. Frank Hurtig, director, Merial Veterinary Services, says a fall parasite control treatment, combined with freezing conditions will help, but producers should not stop there.

“Freezing conditions will help kill some of the parasites on pastures,” Hurtig says. “Producers should consult their veterinarians about the best time to treat for parasites, but cleaning up cattle in the spring also can help reduce the overall parasite load that can affect cattle's performance.”

He adds that in Southern climates, it is even more important that producers consider parasites on pastures - they cannot count on a freeze to do the work for them.

“In climates in between North and South, where temperatures may be moderate one week and freezing the next, producers need to remember that as long as cattle are grazing, they can pick up parasites,” Hurtig says.

To demonstrate this, a study was conducted in Oregon - a place where temperatures can fluctuate - during two weeks in the winter. During this time, temperatures never got above freezing. Results varied; however, parasite-naïve calves turned out on contaminated pastures on one operation picked up as many as 200,000 nematodes.

“This study shows that if cattle are exposed to pastures they continue to ingest parasites during the winter months,” Hurtig says. “It is essential to break the life cycle of the parasites when they are in the cattle to help reduce pasture re-contamination.”

He adds that producers should discuss a strategy with their veterinarian to help ensure cattle are protected from parasites all year.

“Producers may not realize it, but parasite control treatments are only effective against worms for the day you treat in the case of some white dewormers, and 14 to 28 days for endectocides, depending on the product used and the parasite,” he says.

He adds that it is equally important that producers are using products that are effective against the economically important parasites in their area. For example, not all products control liver flukes, so Hurtig says producers need to make sure they use a product labeled for liver fluke control.

Parasite control has been identified as the most economically important practice to beef production. However, Hurtig says, for a parasite program to be most effective, producers should use products they can trust.

“Fall is an excellent time to start; however, following that with a spring treatment is important to help ensure parasites are not robbing cattle of performance throughout the year,” he says.