Strategic use of anthelmintics can help control worms in beef and dairy cattle. (Photo by Robert Waggener)

When it comes to worm control in beef and dairy cattle, what are the most common mistakes that producers make?

“Not using anthelmintics strategically, and not monitoring the effectiveness of the products being used,” responded Dr. Tom Yazwinski, professor of animal science at the University of Arkansas, Fayetteville.

Timely use of dewormers is important in an attempt to lessen the parasite population before economic losses occur and before the worms heavily contaminate pastures with eggs which result in more parasites.

If you operate a dairy, younger and replacement heifers should be treated at least every spring and fall until they become part of the milking herd. An ideal time to treat momma cows is when they freshen.

If you’re a cow-calf operator, a good time to deworm the momma cow is also at freshening, and then the calf should be dewormed at weaning, or maybe earlier on some operations, Yazwinski said.

How often that calf receives a dewormer after weaning is dictated by many factors, including whether the calf is being kept as a replacement or managed as a stocker or backgrounder.

“If it’s a spring-born calf that was weaned and treated in the fall and is being kept as a replacement, you would typically treat the following spring and fall,” Yazwinski noted.

“If it’s a fall calf that weaned and was treated in the spring, then you would typically treat again that fall and the following spring.”

Stocker cattle present particular challenges when it comes to internal parasite control because the calves are often placed into operations during all seasons and from all regions of the country.

Further, a mixed group of stocker calves has typically received a broad range of prior parasite exposure and parasiticide treatment, and they are often grazed at high stocking rates on heavily contaminated pastures.

“The stocker/backgrounder operation is where the major impact of worms is, and because of this it’s important to know what products to use and when to use them,” Yazwinski said. “Unfortunately, the stocker cycle of production in the U.S. is the hardest one to give any sort of general recommendations on [regarding] how to control worms.”

A paper that Yazwinski and colleagues co-authored for The Bovine Practitioner recommends the following tips for proper use of anthelmintics in stocker operations:

  • Use a dewormer for internal parasites and a different product for external parasites.
  • If a combination of two anthelmintics is being used, it is vital that the two products be of different modes of action, and that each product is given at the full, labeled dose.
  • Whenever an anthelmintic is administered, it should be given at a dose rate equal to or greater than the labeled dose for optimal efficacy, as contrasted to a partial dose that kills few worms and propagates resistance.
  • Proper dosing is particularly important and problematic when using topicals (pour-ons).
  • Evaluate the effectiveness of the anthelmintic.

When using dewormers, it’s extremely important to perform fecal egg count reduction tests (FECRTs).

FECRTs consist of two fecal egg counts (FEC), says Larry Hawkins, senior technical services veterinarian for Bayer Animal Health.

“The first FEC is taken the day of treatment. That is followed by a second FEC 14 days later, or 30 days later if an extended-release product is being used,” Hawkins said.

Yazwinski recommends performing FECRTs with 10 to 20 animals, and making sure the same animals are used for both the first test and the follow-up samples.

“You want the FECRT percent reduction to be at least 90%. If you don’t get that, then your product isn’t working at a level to be considered effective,” he said.

“For example, the drug you are using may not work for a particular herd, in which case you want to go to a different class of drug or combine your drug with another drug from a different group.”

Yazwinski encourages producers to coproculture eggs for genera specifics as FEC reductions are a function of the drug and the genus of worm.

If animals are in a drylot or on clean concrete (free from post-treatment challenge), then wait until day 28 for the post-treatment FEC and coprocultures, thereby giving some time for the partially affected nematodes to resume egg production, he said.

Since worm burdens and the effectiveness of deworming programs are operation-specific, Yazwinski encourages producers to work with a large-animal veterinarian versed in parasitology and in developing sound treatment programs.

“And arm yourself with knowledge, because a worm you ‘know’ is an easier worm to control,” he said.