Using parasiticides in cattle without considering the active ingredients in those products presents dangers for an operation, according to a "Quick Tips" announcement from Zoetis.
Using different parasiticide active ingredients can extend the effectiveness of parasite control products and play a significant role in the management of healthier cattle, Zoetis said.
Some common, yet misguided, management practices can lead to an operation unintentionally increasing resistance in parasites, the company said, explaining that one type of parasiticide — macrocyclic lactones — saw the first documented case of resistance approximately 14 years ago, and now Cooperia and Haemonchus parasites have been demonstrated as resistant to macrocyclic lactones in more than half of all operations examined.
Zoetis said parasites still must be dealt with, but cattle producers need to find a balance in their management practices.
Zoetis noted three common active ingredient families and how they work to control parasites:
1. Benzimidazoles — This active ingredient family depletes energy reserves in parasite cells and inhibits the elimination of waste — actions that appear to play an essential role in having a lethal effect on worms because it prolongs the time the parasite is exposed to the drug.
2. Macrocyclic lactones — Microscopic worms experience paralyzed pharynx, body wall and uterine muscle when exposed to macrocyclic lactones, which leads to death. This active ingredient works by binding to receptors that open up parts of the nematode to allow the influx of chemicals that cause the paralysis.
3. Imidazothiazoles — This group of parasite control products stimulates muscle contractions in worms that leads to paralysis.
The judicious use of parasiticides with different modes of action will control parasites in a herd and also help keep products effective for longer in the industry, Zoetis said.
The following tips should be considered when developing a management plan for parasiticides, Zoetis said:
• Base dosing on accurate animal weights. Underdosing is a contributing factor to parasite resistance. Accurate weights help drive accurate dosing, which can help ensure product efficacy.
• Use careful management practices. A growing trend calls for replacing the current practice of repeated dosing of whole groups of animals with a move to target selective treatments to animals showing clinical signs or reduced productivity.
• Use different active ingredients to reduce risk. Most of the commonly used parasiticides are either benzimidazoles, macrocyclic lactones or imidazothiazoles. Thus, resistance to one particular compound may be accompanied by resistance to other members of the same group — also known as side-resistance, Zoetis said. Theoretically, resistance may be delayed by using products with different modes of action annually between dosing seasons.