Q. I wanted to ask if any vets or horse owners have heard of problems with the Quest wormer. I have heard from two different people in two different horse areas that this wormer has caused some problems for horses such as stomach aches or mild colic, and a family member's gelding got a belly ache after being wormed with Quest. If anyone has heard of this, I'd really like to hear about it. I'm hesitant to use this product if there's even a slight chance it might cause a problem. Thank you very much.


A. Quest is an effective dewormer when used as directed. It has a broad spectrum of activity, killing the majority of commonly encountered internal parasites, including the sometimes difficult small strongyles. As with some other highly effective dewormers, if the horse has a large parasite burden, killing large numbers of parasites might produce some irritation or inflammation in the intestinal wall in response to the dead parasite stages that are killed off. This might in turn cause some abdominal discomfort. If your horse has been on a reasonably good parasite program, it is unlikely that this product will do anything other than enhance his health by reducing his parasite burden. This product is very effective when used with other products, such as Strongid C, to virtually eliminate parasite loads.

About the Author

Richard D. Mitchell, DVM

Richard D. Mitchell, DVM, has served many times as official veterinarian for the US Equestrian Team in multiple disciplines, and he has a keen interest in lameness and advanced imaging. He also maintains an international clientele that keeps him traveling a great deal.

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