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Deworming through the Winter

A member of the American Association of Equine Practitioners offers advice on deworming during the colder months.


Just how severe are parasites on horses during the cold months of the year, and should I tube or paste?


Winter weather can increase the metabolic demand on the horse's body. Under these conditions, problems (like parasitism) that during nice weather might not have been very severe can tend to be magnified.

In that circumstance, I would say internal parasitism should be addressed prior to the onset of cold weather, to help out your horse as much as possible. I would strongly encourage everyone to speak with their horse's veterinarian about a deworming strategy that works for your horse(s). Even among my own clients, I have found it impossible to make generalized deworming recommendations, because everyone's situation is so different.

As to the second part of your question: Medically, tube and paste dewormers both do a good job deworming the horse. Paste dewormers are certainly more convenient, but have gotten a "bad rap" in some circles due to perceived lack of efficacy. I have found that administering paste dewormers is not as simple a procedure as it would seem. Here are a few techniques to follow to make sure you have good results:

  1. Make sure the horse's mouth is free of all grass, hay, and feed. I find this to be the #1 problem when using pastes. When feed is in the mouth, the paste adheres to it, and makes it relatively easy for the horse to spit out.
  2. Put the entire length of the paste dispenser into the mouth, pointing towards the back of the mouth. I also insert the paste starting at the corner of the mouth (where the bit sits). When the paste is injected as far back into the mouth as possible, the horse has less of a chance to spit out the medication.
  3. After injection, stay with and monitor the horse for swallowing. I have seen many horses that have figured out the "trick" of holding the paste in their mouths for several minutes, then spitting it out. My technique involves lifting the horses head into the air, letting them chew the paste, and waiting for them to swallow. This will be greatly aided by not having any food in the mouth when you start. I certainly don't have any problem with tube deworming horses, but I've found that if used correctly, the pastes are much simpler for me and easier on the horse.

-Dr. Reece Myran, member of the American Association of Equine Practitioners