Bonds says cows are normally treated with a pour-on at gathering time or anytime they’re in working pens. Also, calves are injected with a dewormer at branding and given a pour-on and a white paste (drench dewormer) at weaning.

“One deworming will sometimes be sufficient in an area where the climate is drier,” she says. “But to be safe, we also treat cows with a white-paste dewormer when we palpate, as she’s already in the chute. The white paste provides an immediate kill.”

Woodruff says persistent control provided by a dewormer should be considered when selecting a parasite control product. “Persistency describes how a dewormer continues to fight parasite infestations after application,” he says. “Increased persistency can result in fewer parasite eggs shed, reduced pasture parasite levels, and increased opportunities for weight gain.”

missy bonds deworming callout

Bonds uses primarily Cydectin® pour-on or injectible, as well as Synanthic® white paste, both from BIVI. She sometimes also uses a different white paste, Safeguard® from Merck. A producer’s dewormer arsenal may also include Dectomax® from Zoetis, Noromectin® from Norbrook, and Merial’s Eprinex®, Ivomec® and a new product called LongRange®.

Harold Newcomb, Merck Animal Health technical veterinarian in northwest Mississippi, says the use of two or more separate classes of dewormers in a concurrent treatment program can help prevent or control parasite resistance.

“There are three classes of anthelmintics (wormers) approved for use in the U.S.,” he says. “They include marocyclic lactones, which consist of injectible and pour-on products such as Ivomec, Eprinex, Moxidectin and generic ivemectin products; the benzimidazoles, which are the white anthelmintics such as Safeguard, Valbazen® and Synanthic; and imadathiozoles, which are Levamasole and Rumental.”

Newcomb says National Animal Health Monitoring System (NAHMS) data indicate that parasite resistance is increasing in the U.S. He adds that concurrent class use, along with pasture and animal management, has shown to decrease anthelmintic resistance in Australia and New Zealand. 

“Concurrent class use seems to work,” he says. “That’s because the number of parasites with genes with resistance to one class of anthelmintic is greater than the number of parasites with genes with resistance to two classes, and the number of parasites with genes with resistance to all three classes of anthelmintics. Using two or more classes concurrently reduces the number of resistant parasites.”

Newcomb says parasite control is the cornerstone of any herd health program, as parasites affect every segment of the beef industry. “The economic impact of parasites was estimated to be up to $195 over the lifetime of a calf in a recent study by Iowa State University,” he says.