Ask the Vet: Worming

Answered by, Mark Haugland, DVM, DACVS, The Woodlands, Texas

Question: I have been using Diatomaceous Earth as a daily dewormer. My veterinarian is suggesting adding Equimax and then Quest paste.

I was reading about kill overload of dead worms. The worm fecal egg count (FEC) is 115. Do you see any concerns? Would there be any concerns for also using this same routine on a broodmare?

Answer: Today much more emphasis is placed on individual animal deworming programs as opposed to herd deworming programs, which has been the standard over many years. There is concern of resistance to dewormers and there is abundant evidence to prove this resistance.

Diatomaceous earth is considered ineffective at controlling parasite load in horses. There are few concerns about using diatomaceous earth, but it is not recommended as a parasiticide. You may ask, if it is not effective then why is the fecal egg count 115, which is considered a light shedder? This would suggest that your horse has good immunity and should only need deworming twice annually. The moxidectin or ivermectin products are a good addition as recommended by your veterinarian. This will also kill bots and, if you get the product with praziquantal, tapeworms are taken care of as well.

This program is safe for a broodmare, but the fundamental aspect of your question is parasite control. Guidelines for this are based on a fecal egg count reduction test. You have obviously done this in the horse that has a 115 count. However, deworming schedules change depending on the egg count. For example:

Light shedder: 200 or less

Moderate shedder:  200-500

Heavy shedder:  greater than 500

Based on the egg count, your veterinarian will prescribe a deworming program tailored to the specific horse. In short, the higher the egg count, the more frequently you should deworm. Therefore, the program advised for the horse in your question could be different than one prescribed for your broodmare or any other horse. It all hinges on the egg count. Consult your veterinarian for his/her protocol on egg counts for your farm. He/she will then analyze the results and tailor a program for all your horses based on which category the individual horse falls into.