CAUTION!!! I wormed my healthy, much loved mare of 27 years last Sunday with Quest Gel (Zoetis) and 5 hours later she was staggering, spinning in circles and depressed. Neurologically unwell. Prior to worming she was relaxed and happy. Was in a large pasture with no access to anything toxic, and was supplied with good quality square baled hay, mineral and loose salt. As well as fresh, clean water. No change in any dietary habit other than adding hay in September. I do not feed grain. The companys response appears to be standard for all of us who have had trouble. They suggest there must be some underlying issue that does not involve their product. I find it odd that the video I see shows horses staggering around, and then dead, just like my horse. They are varying in age, and appear to well cared for and healthy. This is not just killing foals and minis, but horses of all ages and size. They must all have similar underlying issues to all exhibit the same symptoms? And these underlying issues seem to spring up shortly after using Quest. Again, somewhat odd if there is no connection to the wormer. And even if it proven this is the case, and they are aware of it, why is not labelled precsription, so it is only used safely, by a veterinarian who can rule out other health concerns? Without obvious signs, the average horse owner may not be aware of an underlying condition. There is no warning anywhere on their packaging that indicates this risk. Made every effort to help her recover, to no avail. We destroyed her on the following Thursday. Am seeing online video of other horses exhibiting the same symptoms as my mare, shortly after ingesting Quest products. So is not an isolated incident. This product had a prescription label in Quebec, but was informed by Zoetis that it was removed due to market pressure. I believe that is unfortunate for all that have suffered an incident such as this, it is horrific to watch. Use extreme caution when worming, and if using Quest products and you have any doubts, consult your veterinarian prior to administration. You may save yourself and your horse much grief. I am not a totally uninformed owner, have worked as a vet assistant for years, as a groom on the track and have owned and wormed horses for 40+ years. My mare was not overdosed. I read everything on the box and insert prior to giving it to her. There was no warning that I was about to kill my horse using this product. Investigation with numerous agencies is ongoing, and will update any new information as it becomes available. HORSE OWNERS PLEASE BE INFORMED OF THE RISKS. If you have had, or will have a similar experience please be sure to report it to the veterinarian, the company and local health agencies. In Canada I am dealing with a department within Health Canada. In the US, I believe it is the FDA. It is too late to save my girl...but there is a problem here, and we can do better for each other and our horses. I for one will not quit until there is a viable solution. And I sure would never use Quest again on ANY horse without a complete health exam performed by my veterinarian.