Gastrointestinal, GI, parasites bring serious concern to equine health. Among the various types of parasites includes the most common nematodes from the Strongylidae family. In the last two years, the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, has detected parasites in approximately 49% of equine fecal samples submitted for parasitology testing. Of this group, 45% of the samples tested positive for the presence of strongyle type eggs while only 3% were roundworms and less than 1% were strongyloides, also known as threadworms.
Strongyle type worms are divided into small and large strongyles.
“We used to worry a lot about the large strongyles, Strongylus vulgaris,” Terry Hensley, MS, DVM, assistant agency director for diagnostic services, said. “Now, we deal a lot with the small strongyles.”
In past years, the routine of administering deworming treatment every two months was effective in controlling large strongyles and other parasites; however, TVMDL technicians are noticing a trend of GI parasites showing reduced susceptibility to treatments.
“We are now seeing some anthelmintic resistance in these classes of parasites,” Hensley said.
“We’ve got to change our mindset on how we deworm and how we control these parasites in our horse populations.”
Hensley suggests lowering resistant levels by possibly muffling the repetition of deworming administration.
“By maybe not deworming as frequently, it will allow the worms in the environment who aren’t resistant to then be able to sort of cross breed with the resistant worms,” he said.
According to the USDA-Animal and Plant Health Inspection Service, APHIS, small strongyles cause colic, anemia, diarrhea, weight loss, poor performance and other problems within horses and livestock.
These migrating parasites, also known as bloodworms, encyst within the intestinal lining of a host so they are less susceptible to conventional deworming medications.
Horse owners and veterinarians should test for resistant worms to avoid unproductive investments in dewormers.
McMaster’s test at the TVMDL
TVMDL offers a McMaster test, a specialized type of fecal floatation that detects the exact quantity of eggs per gram. Technicians take two grams of a feces sample diluted within a saturated salt mixture and place it on a McMaster’s chamber which withholds a marked grid with a known volume underneath.
“Due to our technique, the lowest detectable limit is going to be 50 eggs per gram,” Mindy Borst, clinical pathology assistant section head, said. “So, if we see one egg under that grid, we know that’s at least 50 eggs. That one egg is going to represent 50 eggs per gram in that horse.”
TVMDL recommends using the McMaster’s test to quantify the parasite load in horses before and after deworming. If results show there are less than 200 strongyle type eggs, the horse is considered a low contaminator. More than 500 eggs per gram of feces indicates a high contaminator and treatment is recommended. Between 200 and 500 eggs per gram may not be associated with clinical disease, but treatment may be justified based on other factors.
Hensley recommends sending in a second fecal sample about 14 days after administering the initial deworming treatment.
“You can see what the egg count difference is after you’ve done your anthelmintic treatment,” he said. “In most cases, you want to see at least a 95% reduction in eggs per gram. If you’re way below that, you could have some resistance in that worm population on that farm.”
Sending a fecal sample
Borst encourages clients to send fresh fecal samples as quickly as possible. Exposure to oxygen stimulates the hatching of parasite eggs which could decrease the attainability of accurate test results.
TVMDL recommends clients collect fecal samples directly from the animal’s rectum. At the least, clients should observe bowel movements and immediately collect from fresh stool.
“I recommend sending it in a plastic sealable bag, like a Ziploc, so that you can press all of the air out of the bag,” Borst said. “Gloves are totally fine as long as you can tie off the glove.”
If a client is unable to submit a sample immediately, Borst suggests keeping it refrigerated.
“Refrigeration is going to slow the maturation process, but definitely don’t freeze them,” she said. “Freezing will denature those eggs and most of them will explode.”
TVMDL facilities in College Station and Canyon offer tests for other parasites like roundworms, tapeworms, and coccidia. Strategic testing helps maintain the health of horses while promoting responsible and cost-effective parasite control practices.
A commitment to ongoing GI parasite management helps promote the long-term health and productivity of equine populations. Frequent deworming could increase the chances of anthelmintic resistance among herds, so farm and ranch security from parasitic worms like small strongyles, can be obtained by monitoring egg counts.
For more information on TVMDL’s test offerings, visit tvmdl.tamu.edu or call the College Station laboratory at 1.888.646.5623 or the Canyon laboratory at 1.888.646.5624.
