Despite significant progress in controlling parasites, too many operations fail to consider active ingredients for specific parasite challenges — or even deworming at all. Failure to deworm calves in the spring can limit the calf’s ability to reach its full potential.

Advancements have made parasite infestations primarily a subclinical issue, so producers assume there is no problem because they don’t see obvious clinical symptoms or death losses, said Dr. Mark Alley, DVM, managing veterinarian, Zoetis. Because the infestations are subclinical, it’s hard to visualize the calves maybe 10 pounds lighter, but, as Dr. Alley said, “In the sale check that makes a difference.”

“Part of the reason for these management decisions comes down to the success of macrocyclic lactones in stopping the loss of cattle due to brown stomach worm (Ostertagia) infestations,” Dr. Alley said. For a time, the industrywide urgency of that problem took the focus away from working to control internal parasites like Cooperia, Nematodirus, and Haemonchus.

However, the inappropriate use of macrocyclic lactones is causing parasite resistance issues, so producers must pay attention to ingredient families when selecting parasite control products. The three most common ingredient families are benzimidazoles, macrocyclic lactones, and imidazothiazoles. The first step is understanding the limits of current management practices. Cattle producers need to work with a veterinarian to diagnose and determine what works in their parasite control program.

As Dr. Alley explains, there are some challenges at the cow/calf level to understand which parasite is present. It is believed older cows develop some resistance to Cooperia. Cooperia, Nematodirus and Haemonchus typically are a more significant parasite challenge in younger animals. “But the only real way to determine which parasites are present is to get cultures or PCR [polymerase chain reaction] of the eggs from fecal samples,” Dr. Alley said.

An example Dr. Alley shares is the assumption that winter weather kills many parasites, specifically the larvae and eggs in the environment. “In reality, cold weather doesn’t have a very big impact on them,” Dr. Alley said.

As soon as warm weather returns enough to grow grass, the parasite resumes its life cycle on the pastures. “As a result, we get really short grass that’s just greening up, and with the right-size, right-age calf, they’re going to start nibbling on grass,” Dr. Alley said. “And when they do graze, they may be consuming some parasites with their first forage consumption.”

Dr. Alley recommends cow/calf producers work closely with their veterinarian to develop an effective parasite management program for cows and calves that addresses