Fall deworming keeps cattle clean until spring

Written by Dr. Jim White on .

There used to be a time when we could look at cattle and know that they most likely had parasites. Today, most of the signs of parasites in cattle are subclinical, not read­ily observable, and may point to a number of other conditions. Calves aren’t growing like you think they should, weaning weights are down or the gains just aren’t what they used to be. Perhaps reproductive efficiency isn’t what was expected or pregnancy rates are lower.

Think of parasites as an iceberg. Most of the problem is unseen, but performance is affected. Parasitism is a numbers game. Cattle can toler­ate a few worms, but heavy infec­tions are detrimental. Worms are more devastating in young animals because they haven’t yet developed much immunity.

If you’ve done a good job pre­venting disease but have not taken a look at your deworming protocol, it’s time to talk with your vet. The conversation may go something like this: “Doc, I’ve been deworming the same way with the same product for years. Do you think there’s a value in making a change?”

Your vet may suggest a fecal egg count reduction test to see how well your dewormer is working and assess the efficacy of your current program. Then you can make an informed decision on what products to use.

Avermectins, such as Ivomec, and benzimidazoles, such as Safe-Guard, are the two general categories of deworming products on the market. Each has different modes of action. A general recommendation is using a benzimidazole formulation either in rotation with or at the same time as an avermectin to prevent parasites from developing resistance. Recently purchased cattle with an unknown dewormer history should receive a benzimidazole dewormer before being added to the herd.

The type of deworming prod­ucts and how they are used may be contributing to an increase in resistance. Cattle producers used to deworm once or twice a year. With the advent of products that doubled as fly control, producers started using them more frequently and seeing less control. If we keep using dewormers indiscriminately, we may lose the efficacy of these tools. To help reduce resistance, proper dos­age is crucial when using products like these.

So, when should producers use dewormers, both to maximize effica­cy and minimize resistance? While every operation will differ, there are general guidelines to follow.

Deworm when it’s best for the cow, not when it’s most convenient for you. It is recommended to deworm cows prior to the breeding season or prior to calving. When the cow has the highest nutrient needs, that is a good time to deworm.

Deworm all new animals so they do not have a chance to contam­inate the herd. Ideally, the new animals are isolated for a few weeks before commingling with the other animals.

Deworm cattle that are on pas­tures heavily infected with parasites due to overcrowded conditions or extended periods of moist, cool weather. Deworming of young stock (weaned calves, replacement females and yearling bulls) is important in the fall because animals less than 2 years old are much more susceptible to negative effects of parasitism.

If you effectively deworm cattle coming off pasture in the fall, they should remain clean all winter. Many effective options are available, including pour-on dewormers, feed-through products and injectables. Consult with your veterinarian and MFA livestock specialists to set up a deworming program that fits your production and management goals.