Test Herd to Avoid Parasite Resistance

Cindy ZimmermanAnimal Health, Boehringer Ingelheim

BIVI logoAs reports of internal parasite resistance to deworming treatments are on the upswing, Boehringer Ingelheim Vetmedica Inc. (BIVI) is urging herd managers to test first, then treat, to avoid both the overuse and underuse of anthelmintics that can lead to a resistance problem.

Overuse is the result of producers deworming too often, and underuse occurs when too little product is administered, according to Dr. Mac Devin, professional services veterinarian with Boehringer Ingelheim Vetmedica, Inc. “In a closed population, if you treat too frequently, the remaining worms are the only ones left to breed,” he says. “Resistance increases with each generation. And if less than the labeled dose is given, again, this leaves too many survivors to pass on their resistant genes to the next generation.”

To establish a resistance management program in your herd, Devin recommends, with the help of your herd veterinarian, first conducting a fecal egg count reduction test to detect if you have parasite resistance in your herd. Two tests are taken; after the first test, treat the entire herd, then come back in 14 days to take another count and then calculate the loss. “Do this test on 20 percent of your herd, or 20 animals, whichever is less,” he says. “We want to see a 90 percent fecal egg production reduction.” Less than that would suggest a resistant population is present.

Secondly, herd managers should do a coproculture. Samples are incubated and then evaluated by a parasitologist to determine the composition of the nematode population.
With this information, cattle producers can determine the most effective program that will minimize the risk of resistance.