Cattle producers could benefit from a more strategic approach to parasite surveillance and control.
John Gilleard, a parasitologist in the University of Calgary’s veterinary faculty, said specific recommendations are impractical because operations differ. However, he said producers don’t always have a good handle on the parasite problems that they may have.
“A lot of the producers assume that doing a fall treatment with ivermectin keeps things under control,” he said. “I think that’s OK for some but for others they’ll be losing money because they’re not having a more strategic approach.”
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Gilleard said producers should consult their veterinarians and come up with a strategy based on their grazing systems and monitoring of parasite burdens.
Fall treatments are typical because producers can use a product that treats cattle for both external and internal parasites.
However, some producers find spring treatments more effective. Others are looking at mid-summer.
Veterinarian Roy Lewis said strategic deworming in mid- to-late summer through a pour-on product or others that are administered through feed or even water if possible can help cattle do better on pasture. Leaving treatment to fall can allow the parasites to run the cattle down.
Summer treatment would give herds with high parasite loads the best bang for the buck, Lewis said, but they would still use a fall product for external parasites.
Gilleard said spring treatments offer benefits to pick up parasites that have overwintered on pastures. Fall treatments won’t protect against those.
“The tricky bit is deciding which producers that applies to,” he said. “Everybody kind of thinks there’s like a blueprint but there isn’t really. Some producers probably don’t need to worry too much. Others are probably losing money because they’re not worrying about it enough.”
Gilleard said the idea of refugia is gaining acceptance to help prevent drug resistance.
In recent years, resistance of some parasites to the ivermectin family of products has been a concern.
Refugia is when the entire herd is not treated. If all animals are treated, then the entire parasite population is exposed to that drug.
“The few that survive will be resistant and therefore you’ve selected for those resistant ones,” Gilleard explained. “If, though, you leave some animals untreated, that allows some of the susceptible ones to survive and compete with the resistant ones in terms of what goes on to the pasture.
“One of the things that’s being advised now is if you’re treating at the herd level, to leave 10 percent of the animals untreated. That way you get the benefits of the drug treatment, but you’re not selecting for resistance as strongly as you would be if you treated absolutely everything.”
He said it is a reasonably safe practice because no producer who leaves 10 percent of a herd untreated is going to lose a lot of money. They could do this randomly or choose the 10 percent that are in the best body condition.
Other strategies include rotational grazing done properly, the experts said.
Most parasites tend to live in the lower part of the grass. Overgrazing could result in cattle picking up more larvae.
“Some guys have the ability of these dry ranges where cattle don’t come back for a whole year,” Lewis said. “That’s a pretty good management strategy because all the larvae are dead because they dry out over the summer.”
Another practical strategy for producers who run both cattle and sheep is to run one species on a pasture one year and the other species on that ground the next year.
Cattle parasites do not affect sheep, and vice versa.
Or, producers could use the dilution technique and run cattle with sheep to reduce parasite loads, he said.
Producers should be using better evidence to determine their treatment programs, both Gilleard and Lewis advised.
Examining grazing systems to see if they could be exacerbating parasite problems, taking fecal samples to calculate parasite loads and monitoring weight gains can all help.
Meanwhile, Lewis said there were some substantiated reports of lice problems this year and some are concerned this is due to drug resistance.
“We haven’t seen drug resistance in lice before. At this stage, we don’t know,” he said.
Products developed to treat fleas and ticks in dogs and cats work very well, Lewis said, and he wouldn’t be surprised if companies aren’t looking at ways to adapt some of them for cattle.
“They show quite the promise because they’d be longer lasting,” Lewis said. “The negative would be withdrawal times.”
