Are parasite problems returning in cattle due to dewormer resistance?
This week’s article comes from the Ohio BEEF Cattle Letter. The newsletter is a publication of the Ohio State University Extension Beef Team. Contributors include members of the OSU Beef Team and beef cattle specialists and economist from across the United States. “Are Parasite Problems Returning in Cattle Due to Dewormer Resistance?” was written by Dr. Michelle Arnold from UK Veterinary Diagnostic Laboratory. This is a follow-up article from last week.
How is it possible to know if dewormer resistance is a problem in a herd? The best way to test is a Fecal Egg Count Reduction Test (FECRT) based on the knowledge that dead worms don’t lay eggs. This test basically involves taking fecal samples from 20 random animals within a production group (cows, calves, or replacement heifers) at the time of deworming and sending them to a laboratory for a fecal egg count (FEC).
Fecal samples are collected again from the same production group 14 days later and those samples are sent to the same laboratory for a second FEC. The second samples do not have to be collected from the same individual animals but do need to be from the same group collected previously.
More: Are parasite problems returning in cattle due to dewormer resistance?
How do you know of dewormer is working?
If the dewormer worked effectively, there should be at least a 90% reduction in the average or mean number of eggs from the first sample to the second sample. “Resistance” is present when the correct delivery of the correct dose of the dewormer to a healthy animal fails to produce at least a 90% reduction in the number of parasite eggs. It is important to understand that a decrease in “anthelmintic effectiveness” or “treatment failure” may be for reasons other than genetic or heritable resistance in the parasite population.
Many factors can cause smaller than expected reductions in fecal egg count numbers including underdosing dewormers from errors in weight estimation, dosing equipment not calibrated correctly and/or not working properly, applying pour-ons to the hair of an animal rather than skin, use of expired products, and errors in sample collection and shipment, just to name a few.
How can we slow the development of resistance to dewormers? First and foremost, we must understand the parasite prevalence (the proportion of cattle with a large parasite load in each time period) in KY cattle in order to properly direct research and extension interventions to lessen the effect of parasites on health and production. Secondly, we have to examine the current level of resistance to dewormers through FECRTs performed throughout the Commonwealth.
Finally, it is important to identify the predominant types of gastrointestinal parasites in our cattle to correctly interpret the FEC. Most of the major parasites in cattle are classified as “strongyles” and their eggs are basically indistinguishable. Weaned calves up to 12-18 months of age are mostly affected by two strongyle species, Cooperia and Haemonchus, both of which produce huge numbers of eggs. Around 2 years of age, cattle develop resistance to Cooperia and Haemonchus but another strongyle, Ostertagia, a more pathogenic parasite predominates yet it does not produce many eggs.
Help available to ID parasite and species
A PCR is now available to identify the parasite genus and species as there are concerns that climate change, intensive livestock management and dewormer resistance issues have fundamentally changed our picture of “expected” parasite burdens in production classes of cattle. To accomplish these three tasks, UK Extension faculty and agents, in conjunction with KBN and Merck Animal Health, have launched a parasite study that is set to begin in the Spring of 2023 in beef cow/calf and stocker operations in KY and we need your herds.
To participate, collaborating herds must be planning to administer a dewormer in BOTH the spring and fall of the year. Producers may use any dewormer they normally use or one recommended by their veterinarian. It is important to understand that dewormer will not be provided to participating herds! Fecal samples will be collected twice in the spring and twice in the fall from the same group of animals.
Producers will be asked to complete a short questionnaire requesting basic information on the herd. Once all the data is compiled, the information will be shared with the producer and his/her veterinarian, if desired. If you wish to be considered for enrollment in this important study, please contact your local County Extension agent and convey your interest in joining.
Reducing unnecessary treatment with dewormers, making sure the dewormers used are effective, and making sure deworming is performed correctly all contribute to fewer resistant genes in parasites. In addition, environmental management will help create safer pastures and lessen the need for chemical dewormers.
Shelby Tedrow is an OSU 4-H & AgNR Program Assistant and may be reached at 330-264-8722 or tedrow.28@osu.edu.
This article originally appeared on The Daily Record: Dewormer resistance: What can it do to livestock?
