Timing is Important When
Deworming Cattle
Stomach worm
The "best" time to deworm may vary from region to region, depending on climate, says Thomas Craig, professor in the Department of Veterinary Pathobiology at Texas A&M.
When cattle are at pasture, Craig recommends deworming about one month after the grazing season starts if you are trying to minimize worm burden in cattle for the rest of the year.
"The worms deposited on the pasture the preceding year (the ones that survived from last year) will be picked up right away — or die during summer heat. If you can deworm and destroy those that are picked up before they have a chance to lay eggs and build up in numbers for the rest of the summer, you can minimize the worm load in your cattle," he says.
"Parasitism is a numbers game, as far as disease is concerned. Cattle can tolerate a few worms, but heavy infections are detrimental," he says.
Ostergia worm
The worms are generally more devastating in young animals because they have not yet developed much immunity. If calves are grazing pastures heavily contaminated with worms, they may develop heavy worm burdens.
Depending on the length of your grazing season, it might pay to treat the animals again at the end of it. "Thus you might want to treat twice during a grazing year — once up front, but not right at the front, and again at the end. This maximizes the effects you get from deworming," says Craig.
"With some of the drugs that have long residual activity, you could worm the cattle at the start of the grazing season and get good control, but probably it's best to let the animals pick up a low level of parasites and gain some immunity," he explains. Then you can clean out the worms and help pastures stay cleaner for the rest of the season.
"Each product has a different time of residual activity — from none at all to very long. Thus, you need to select the product depending on your situation."
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