– Dr. Jeff Lehmkuhler, PhD, PAS, University of Kentucky
Available since the ’80’s, is it still effective?
Spring is my favorite time of the year as the flowers bloom, turkeys begin gobbling and the grass takes off. The grass has jumped quickly with the rain and warmer temperatures the last few days. I think we all can agree there is some joy in knowing when the last bale of hay is fed for the winter. However, with spring comes many management challenges beef operations must tackle. These include grass tetany, frothy bloat, dystocia, and tetanus to name a few. During this time frame is always when both internal and external parasites become more prevalent. Many beef operations will apply some level of management to control parasites that can rob nutrients from the cattle. This begs the question “Are you controlling what you think you are controlling?”
During the spring and fall of 2023, University of Kentucky Cooperative Extension Agriculture & Natural Resource county ANR Agents, Kentucky Beef Network facilitators as well as Dr. Arnold and I set out to assess the prevalence of internal parasites in Kentucky beef herds. Additionally, many of the anthelmintics or deworming products have been on the market for decades (1960’s for levamisole and 1980’s for ivermectin), so we wanted to evaluate the efficacy of products being utilized by Kentucky beef herds. Working with the Kentucky Beef Network, Merck Animal Health provided financial support for the field study and evaluation of the fecal samples collected.
A total of 180 fecal collections were performed. Each fecal collection had a target of 20 fecal samples from animals within the same age class. Age classes included mature cows or growing calves / replacement heifers. Beef producers were allowed to use whatever products they wanted. Product as well as route of administration were recorded. Products were classified as either macrocyclic lactones (ivermectin, moxidectin, eprinomectin, doramectin), benzimidazoles (white pastes/levamisole), or combination of more than one product. Fecal samples were sent to a commercial laboratory for counting fecal eggs and classification based on visual appearance.
As one might expect, pour-on products were widely utilized. These products included most of the first generation or name brand and second generation or generic products. Combinations of products were mostly administered to feeder calves in backgrounding/stocker programs.
When looking at prevalence of internal parasites through the fecal egg count method, stomach worm eggs were present in 60% of mature and 78% of growing animal samples. Cooperia were observed in 22% of mature and 74% of growing animal fecal samples. These two parasites were the most commonly observed with other internal parasites noted but less frequently.
The World Association for the Advancement of Veterinary Parasitology set guidelines for studying anthelmintic resistance. Products used in cattle that result in less than 90% reduced in fecal egg counts are considered to have resistance. Further, USDA label claims for anthelmintics require a 90% or greater fecal egg count reduction (FECR).
The samples gathered were filtered leaving only groups containing at least 18 animals in the same age class and had an initial fecal egg count of 10 eggs/3-gram sample. This left 80 groups or only 44% of the total sampled in the analysis. Of these qualifying groups, macrocyclic lactone products on average provided a FECR of 74.5% in mature animals and 61.6% in growing or immature animals. Benzimidazoles and combinations of products resulted in greater than 90% FECR regardless of age.
We looked at the data another way to attempt to determine if internal parasites differed in their susceptibility. We found that in growing cattle administered a macrocyclic lactone product, the FECR was 78% still below the 90% threshold for total egg counts. The FECR was observed to be slightly higher at 86% for stomach worms but only 77% for cooperia. Some anthelmintics have shown to have lowered efficacy in other livestock species for cooperia. Additionally, when we looked at route of administration, pour-on macrocyclic lactones had a 63.9% FECR while injectables were only slightly better at 68%.
This field study provides a snapshot of the internal parasite prevalence in the state’s beef herd. Additionally, the study provides some evidence that additional work on anthelmintic efficacy is warranted. Cattle owners are encouraged to work with their veterinarian to develop a protocol for monitoring internal parasites and effective treatment approaches.