08/21/2026
Caterpillar Toxicity … I have taken this from the internet so it is more comprehensive than I can explain.
“When a horse eats tent caterpillars, the tiny barbed hairs (setae) pierce the gut lining. This lets bacteria enter the blood.
Signs vary depending on whether the horse is pregnant or develops heart or gut inflammation.
Reproductive Signs (Mare Reproductive Loss Syndrome)
*Early or late pregnancy loss and sudden abortion
*Expulsion of fetal fluids and membranes
*Vulvar discharge
*Weak or dying newborn foals unable to stand or nurse
Heart and Systemic Signs *(Pericarditis)High fever and low energy
*Fast heart rate and muffled heart sounds
*Swollen neck veins (jugular distension)
*Fluid swelling under the belly and lower body (edema)
*Trouble breathing
Digestive and General Signs
*Mild to severe colic
*Weight loss and diarrhea
*Muscle stiffness, weakness, or loss of coordination “
We were able to save this last foal through multiple treatments.
The mare was palpated to see if we could confirm the foal was alive. We had no success. We chose to believe she was still alive and started Aeria on Regumate, Antibiotics, and Omeprazole (tummy protection). We did this for 3 weeks and then monitored. A second palpation 10 days later confirmed movement! We were so excited. We weren’t sure how this would effect the foal and expected problems with weakness and possible sepsis. She was born very lax on her back legs but had good energy and was smart and nursing. We started her immediately on Excenel and a small dose of Selenium for her ligaments. She has responded really well and is a little spitfire!
We are grateful we were able to save one precious little soul. We have a plan for next year as we anticipate another bad year. We have NEVER seen caterpillars in this number. 😳 It was something out of a horror film!
Best options if you have lots of caterpillars…
1. move your horses 100 meters from infected trees
2. If your horses have been exposed start them on Omeprazole to protect their stomach.
3. If they are in foal I would start them on an antibiotic
4. Possibly consider Progestin (Regu-Mate) to maintain the pregnancy but confirmation of live fetus is super important. Always refer to your veterinary doctor for advice.
* This is just the protocol we have put in place. We are not veterinary professionals but we do work very closely with our long time veterinary clinic. This was a new experience for all of us.
