A limited number of anthelmintics (dewormers) — and active ingredients — are available on the market, which is why it’s important for cattle producers to know how each product works and how these products can best be utilized.

“Dewormers interfere with the parasite’s bodily function at the cellular level, and by disrupting that cellular function, they cause paralysis and death,” said Dr. Mike Nichols, a veterinarian with Boehringer Ingelheim. “Producers are often encouraged to rotate parasite control products in order to improve efficacy and enhance herd performance.”

The challenge is that a producer may not actually be using a different type of anthelmintic, he said. Macrocyclic lactones and benzimidazoles are the two general classes of deworming products on the market, each having different chemical structures and different active ingredients: benzimidazoles include oxfendazole, fenbendazole and albendazole; macrocyclic lactones include eprinomectin, ivermectin, doramectin and moxidectin.

Benzimidazoles are white wormers that are typically administered orally. These short-acting products are generally very effective against adult worms and other intestinal parasites but have little residual killing power, Boehringer Ingelheim said in an announcement.

Macrocyclic lactones have a longer duration of activity against a much broader range of parasite stages than benzimidazoles. These dewormers are available in both pour-on and injectable formulations.

“It’s important to remember that there are multiple active ingredients within each class, all of which use the same mode of action to eliminate parasites,” Nichols said. “By administering a parasiticide from the opposite class, producers can take advantage of an alternative mode of action to improve deworming efficacy.”

Nichols pointed out that monitoring the effectiveness of treatment can help determine if and when using a different class of products is necessary. By performing a fecal egg count reduction test, producers can assess the effectiveness of products being used. A herd veterinarian can advise on the proper method and assist with conducting the test for the most accurate results.

When conducting a fecal egg count or a fecal egg count reduction test, it’s also important to determine the predominant worm species present in a herd, Boehringer Ingelheim said. Veterinarians may suggest the use of concomitant therapy — the practice of using two or more dewormers of different classes — to ensure that animals are protected.

This multipronged approach allows producers to kill a greater percentage of the parasites present in their cattle herd, Nichols said.

“By incorporating both macrocyclic lactones and benzimidazoles into a parasite control program, thus utilizing two different modes of action, we can kill a larger spectrum of parasites within the herd and more effectively reduce the risk of them developing resistance on any given pasture,” he said.