Parasite Problems: Part III (Squeamish Horse Owners Read with Caution)

Updated: 2 days ago

How often do we confuse parasite problems with gastric ulcers? That is the question that came to mind this morning as I picked pens in the rain. Unfortunately, I do not have the answer to that question, and I don't have any way to find out, but it's an interesting question to ponder considering my own experiences (read Parasites are STILL a Problem Part I and Part II) and a new experience told recently by a friend in Oregon. Just last week, she told me the harrowing story of her horse being scoped for ulcers and finding a terrible bot parasite problem instead! *Squeamish horse owners read ahead with caution!



Before I tell you the story of Star and Lori, I'd like to share with you the results of my follow-up fecal egg count. Stella and Coulee, the highest strongyle shedders in my little herd, were retested three weeks after deworming with the Zoetis QuestPlus (moxidectin + prazinquantel). No parasite eggs were found in either sample which was great news! However, I am going to do a follow up fecal egg count this summer before deworming again.


In retrospect, I think the following most likely factored into my high strongyle egg count in January...

  1. Introducing two young horses into the herd from questionable management conditions. I'm assuming that the unthrifty 2 year old brought in a huge load of parasites to my property.

  2. Not allowing the compost to do its thing long enough to thoroughly heat the bin and kill most of the parasites.

  3. Not being able to remove the manure waste from my property is posing a problem. Four horses on 5 acres is a lot even with regular manure pickup and composting.

Results of follow up fecal egg count after deworming.

Back to the story of Lori and her gelding Star! I called her up last week to discuss the conditions and factors that led to the stomach scoping, what they found, and what she learned.


Star is relatively new to Lori's small herd group in Southwest Oregon. Not long after arriving in his new home, Star developed an exercise induced cough that Lori assumed was caused by smoke from a severe fire season in 2020. The vet thought the cough could be allergies, but it got worse through the winter. Other symptoms developed such as weight loss, finicky eating, and excessive anxiety. With such symptoms, Lori decided to scope for gastric ulcers, and what was found surprised both of them! The vet said it was the worst bot infestation he had ever seen. You can see them embedded into the lining of the stomach in several pictures below!


Bot infestation found in the stomach.


Despite deworming in the fall, Lori's overall parasite prevention program had become minimalist in recent years just as mine had. A fecal egg count test would not have found bot egg larvae (there is no fecal test for bots), but the heavy bot fly infestation and the little yellow eggs on the legs and chin every year were sure signs that the horses had a bot problem. Of course hindsight is 20:20, but this is yet another great example of proper diagnosing rather than guessing. I applaud Lori's intuition to scope her horse rather than just treating Star as if he had ulcers. It has saved her a great deal of time and money in the long run.


The vet further predicts that the original cough was likely caused by parasites (other than bots) and recommended deworming with ivermectin. The day after administering Ivermectin, Lori found a plethora of dead larvae in all horse's manure.


After hearing Lori's story, I called up Horseman's Laboratory to review their recommendations for bot prevention. Dr. Byrd, the founder and parasitologist behind Horseman's Laboratory, laid out some excellent recommendations that you will find below.


Dr.Byrd's recommendation for bots:

- assume that you have a bot problem if you see the flies and/or eggs on the horse

- deworm with ivermectin and/or moxidectin paste in late fall/early winter

- scrape/remove the bot eggs daily during the late summer/fall season

- 6 months or more of composting will kill the eggs


Thank you very much to Lori for sharing her story and to Dr. Byrd for his professional recommendations to control bots. I will be continuing this parasite prevention blog series later in 2021, but in the mean time, I highly recommend engaging your local veterinarian in a serious parasite discussion. Parasites are intimately connected to your horse's nutrition program and overall health and wellness. I am certainly going to make it a greater priority in my annual horse care than I have in previous years.


On Course Equine Nutrition now offers a 3 Month Guided Nutrition Practice PRO service that includes a prepaid fecal egg count kit from Horseman's Laboratory, however these fecal egg counts can not identify bots, pinworms, or tapeworms. These parasites can only be identified visually (bot eggs on legs or pinworm eggs on the anus), by geographic location, and horse history. It is this last factor, horse history, that brings up the possible cross diagnosis of ulcers and parasites. We often describe gastric distress as a symptom of inflammation, and don't parasites cause inflammation!?! Many species of parasites will spend part of their life in some part of the horse's digestive system, so I highly recommend ruling out parasites before and during ulcer consideration. Again, consult with your veterinarian and make fecal egg counts a regular part of your deworming program.





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