Quest, Quest Plus, Zoetis and a Horse Named BOGO

September 24, 2015 § 12 Comments

Brought back to NotABreed by a video of a horse named BOGO…

First, let me apologize to the thirty or so commenters as I apparently wasn’t receiving notifications so didn’t check!

I have found this past year or so that I try NOT to watch videos or read stories about animal abuse – I think I burned out on this blog which is probably why I haven’t written in a long time.  The constant horror stories about what people do to horses, dogs, cats, all animals, just got to me.  Yes, way-back-when, I forced myself to watch videos of horses being slaughtered, read all the articles and looked right at those horrifying photos without looking away.  That’s what got this blog started, but eventually, all you do is get mired in the abuse that society as a whole heaps on the innocent animals.

Eventually something’s gotta give.

This video of Bogo is very hard to watch.

Since it had crossed my feed several times, eventually I stopped quickly scrolling by and read the description.  I remembered years ago hearing rumours about Quest and its history with horses.  I joined the Facebook group, mainly to leave a note paying my respects.  I’ve watched the posts to the group, and what got me to dust off the laptop and do some research with the intent to get to writing was a letter that was posted; a letter that was in all likelihood not supposed to get out to the general public (I will post a copy below).

While the parent company of Quest; Zoetis, seems to have never responded directly to anyone other than to say “our product is safe when used properly”, that is IF you can get hold of them, the evidence seems to be to the contrary.  On their website, under the list of wormers they have the following warning:

Do not use QUEST Gel or QUEST PLUS Gel in foals less than 6 months of age or in sick, debilitated and underweight horses. These products should not be used in other animal species, as severe adverse reactions, including fatalities in dogs, may result.

It’s interesting to note that there are five other products listed, with no warnings other than for these two.  It’s also interesting to note that these two products are the only products that contain Moxidectin as an active ingredient (more on that later).

A quick search such as “quest wormer horse reactions” shows a long list of links with titles such as “please put my mind at ease” and “my big scare using quest dewormer”.  There ARE a multitude of stories out there.  There are no less than 10 separate questions/forums dedicated to Quest on Chronicle of the Horse (COTH) alone.  Then there are all the stories being posted on the BOGO page…

Almost without deviation, story after story saying the following:

  • Gave my healthy horse Quest
  • Sudden onset of symptoms (usually within 24-48 hours)
  • Symptoms present as colic and/or neurological
  • Couldn’t eat or drink
  • Horse dies or is euthanized (or sometimes barely survives but not without extensive veterinary support)

I’m seeing that very young or old horses, underweight horses, and specifically ponies and smaller are the most affected.  That being said, there are a large amount of horses that are full size, healthy, happy and now dead after using Quest.  Another common thread seems to run within American Paint Horses and potentially select Quarter Horse lines.  Another potential side-effect seems to be “burns” and ulceration of the lips and/or inside of the mouth.

The creator of the account, quite a while ago, commented that she’d had over 100 stories sent to her by that point.

Zoetis “Response”

Here is the letter from the director of Equine Veterinarians and Past AAEP President, Tom Lenz to veterinarians:

Good afternoon,

Recently, a video was shared on Facebook of a horse exhibiting neurological signs. The horse’s owner implied (and continues to imply) that these signs were caused by QUEST® dewormer. The post was shared and reposted numerous times without verification that the product was indeed the source of this horse’s issue.

The Facebook posting stated that QUEST® was given one day prior to the onset of the clinical signs and that the horse’s condition quickly worsened despite treatment, resulting in the owner’s decision to euthanize the horse a day later – 2 days post administration.

The Zoetis Veterinary Medical Information and Product Support (VMIPS) team was contacted by the horse’s owner on August 19. While it is inappropriate to share many details of the case, the VMIPS investigation revealed:
The Quest® was administered on August 5th, two weeks before Zoetis was contacted
The horse was under-dosed – a 700-750 lb horse was given a 200 lb dose of QUEST®
The horse was an unvaccinated yearling. It had never been vaccinated for West Nile (WN), Rabies, nor the viral encephalitides (Eastern – EEE, Western – WEE, and Venezuelan Encephalitis – VEE)
The neurological signs began over 12 hours after the QUEST® was given
The horse presented with a very high fever of 105.3
The neurologic signs and fever were non-responsive to steroids and NSAIDs and the horse’s condition deteriorated rapidly
The only diagnostic samples collected were serum at the time of the acute presentation.
IgM ELISA for WN and EEE were negative which the lab indicated can commonly occur with acute onset as there is not sufficient time to elicit an antibody response.
Retesting was not possible as no blood samples were drawn after the original visit.
The horse did test positive to Equine Protozoal Myelitis (EPM). The significance of this positive result is unclear.
The owner elected euthanasia on 5 August due to poor response and the deteriorating condition of the horse.
No necropsy or other diagnostics were pursued.

Because only limited diagnostics were performed, and there was no necropsy, it is difficult to determine an accurate diagnosis. However, the clinical signs and condition of the horse are not consistent with an adverse reaction to QUEST® nor with the product’s well established safety profile. It addition the horse was under-dosed by a factor of 3.5X. Based on the facts presented, we conclude that it is highly unlikely that this incident was related to administration of QUEST®.

If you wish to speak to our veterinarians directly with any concern or question, please call 800-366-5288 or 888-Zoetis 1 (888-963-8471 option #2) or call Dr. Amy Poulin at 908-361-5825.

I have attached two documents related to the safety of QUEST® that may help if you get inquiries from clients. We will continue to actively monitor the situation but have no response planned at this time.
Thank you

NOTE:  Where he says the “horse did test positive to Equine Protozoal Myelitis (EPM)”, the owner states the horse tested positive for exposure to EPM, and yes, there’s a difference.  It’s also important to note that Bogo was under-dosed.  Why is this important?  Because it is directly contradictory to the common response from Zoetis that the horse must have been overdosed.


NOTE:  It may be important to note that I did a fairly wide study as to how Moxidectin works.  If you’d like to see those notes (the “Long Version”), I will post it later and provide a link.  The fact of the matter is, after understanding how Moxidectin works, I’ve quoted some points below that I believe to be true to my understanding, and the WAY it works is important but may put you to sleep reading it.

Short version:

Moxidectin “blocks the transmission of neuronal signals”… of parasites.

Come on!  No one can see correlation between blocking neurological signals in parasites and a horse having what looks like a neurological reaction to the drug?

Two points to note from the above-linked page:

  • Young horses, particularly newly born foals, showed typical neurotoxic symptoms after slight overdose, which can be fatal. Probably because the blood-brain barrier is not completely developed in newborns.
  • As a general rule, cattle, sheep, goats and horses tolerate moxidectin very well at the therapeutic dose.

(their bold)

Also, these are the symptoms listed for Moxidectin Poisoning, which they blame on “overdosing” (from the same article linked above):

  • Ataxia (uncoordinated movements)
  • Hypermetria (excessive or disproportionate movements)
  • Disorientation
  • Hyperesthesia (excessive reaction to tactile stimuli)
  • Tremor (uncoordinated trembling or shaking movements)
  • Mydriasis (dilatation of the pupils); in cattle and cats also myosis (contraction of the pupils)
  • Recumbency (inability to rise)
  • Depression
  • Blindness
  • Coma (persistence unconsciousness)

Looks to me like everything I’ve seen and read regarding symptoms of horses given Quest.  With one small DIFFERENCE.  In at least the case of BOGO, the owner very specifically UNDER-dosed him.  So where is the disconnect?  Why can’t Zoetis see that there is a potential for otherwise healthy horses dying from this drug?

So beautiful. Heartbreaking.


In Closing

These are the things I see:

  • Moxidectin seems to be the main culprit in the issue regarding Quest wormers
  • It’s possible there’s a connection to EPM, whether the horse has only been exposed to EPM or has had it full blown (I note this because I have seen a few other cases where the horse had EPM)
  • Moxidectin seems to at a glance have adverse effects more often in Paints and Quarter Horses as far as breed is concerned (and there are specific dog breeds that are “sensitive” to Moxidectin, so why not horses?)

WARNING:Dogs of some breeds are sensitive to moxidectin…, other macrocyclic lactones or other drugs (e.g. emodepside) that can cross the blood-brain barrier…

  • Miniatures, ponies, and young or very old horses are most at risk (due to size, I have to allow for some error regarding dosage on these smaller animals)
  • Historically, and I use the word historically because these stories are online from as far back as 1997 and possibly earlier, Zoetis has blown off absolutely any whisper of correlation between Moxidectin in their products and a multitude of horses who have died, by victim blaming.  This I find reprehensible.  While I understand that yes, humans make mistakes – I would think at some point Zoetis would start looking into the issues.  At the very least, they could add a warning to their website and the product packaging regarding potential DEATH from a slight overdose.

I know my horse, and I’m pretty sure I’m close when it comes to guessing his weight.  But I wouldn’t bet his life on it.

SHOULD READ: Your horse may react adversely, and even die.

Where’s the Warning?


If you have had an issue with a worming product, ANY worming product, and would like to answer a few quick questions, I will take the time to enter all information into a spreadsheet and (a) see if I can find any trends or other representative selections, and (b) post those trends on my blog for everyone to see and analyze.  Your personal information will not be revealed, and I will not email you unless I have a specific question regarding your particular incident.

If you would like to take part in my little study, please copy and paste the short questionnaire below into an email, answer the questions, and forward to me via email at notabreed(at)outlook(dot)com



  • Breed:
  • Age:
  • General health of horse prior to incident:  (e.g. healthy, overweight, underweight, etc.)
  • Time between administering wormer and onset of symptoms:
  • Symptoms:  (e.g. colic, neurological symptoms including e.g. stumbling, falling, etc. see below for complete list)

Complete List:  Ataxia (uncoordinated movements), Hypermetria (excessive or disproportionate movements, staggering, twitching, etc.), Disorientation, Hyperesthesia (excessive reaction to tactile stimuli), Tremor (uncoordinated trembling or shaking movements), Mydriasis (dilatation of the pupils), Recumbency (inability to rise), Depression, Blindness

  • Name of Product used:
  • Final result:  (e.g. death, recovered and length of recovery time, permanent issues and list of issues)
  • Year problem happened:
  • Vet called:  yes/no
  • Vet comments:
  • Necropsy done:  yes/no (if yes, inclusion of necropsy results would be greatly appreciated)
  • Has your horse ever been diagnosed with a problem prior to the incident:  yes/no (if yes, please note what e.g. EPM, founder, heaves, etc.)
  • Reported to Manufacturer:  yes/no
  • Response to report if yes:
  • Feel free to add photos, although I will not post them unless you give me advance permission.

Tagged: ,

§ 12 Responses to Quest, Quest Plus, Zoetis and a Horse Named BOGO

  • Glad to see you are back.

    Condolences to the owners of this poor horse; he was beautiful and yes, the video is disturbing and hurts my heart.

    Moxidectin normally has a limited brain penetration in ungulates due to the blood-brain barrier. Some animals may have a genetic mutation that does not express an active glycoprotein, and therefore they have a poor resistance to the drug crossing the blood-brain barrier. This may be a reason for Bogo’s neurological symptoms.

    It’s too bad that an autopsy was not done which could shed more light on the cause of his neurological problems. RIP Bogo……..


  • Zoetis says:

    We read your blog post and wanted to reach out to offer some helpful information. It is important to us that you know how passionate we are about our customers and the animals in their care. At Zoetis, we adhere to strict safety and quality standards in everything we do. We take reports of adverse events seriously and promptly investigate and assess each case. All adverse event reports are submitted to the U.S. Food and Drug Administration in accordance with Regulatory requirements.

    Quest® has an 18-year record of safe and effective use since its approval in the U.S. in 1997. We carefully reviewed data from adverse event reports, and this has shown the safety record of Quest® remains consistent. Should you have any questions regarding Zoetis products, we invite you to contact our Veterinary Medical Information and Product Support Team directly at 1-888-963-8471.


    • Not A Breed says:

      If you take safety so seriously, why are people having such difficulty getting in touch with you? If you read the comments on the BOGO Facebook page, over and over again people are being put on hold for HOURS and then being disconnected!?!
      Then, when people DO manage to contact you, they get zero response or follow up, but instead you seem to rather just send out emails to vets on how to ‘handle’ the situation if anyone asks questions.

      Personally, I feel your efforts are rather poor…

      Beyond that, did you actually READ my article? Why not take the time here, now, and answer some of the questions and concerns? What about the correlations I’ve noted? Don’t just blow me off with a pat, standard response. Your response was neither ‘helpful’ nor ‘informative’.


    • Concerned says:

      Then why aren’t you taking owners experiences seriously? There are over 100 serious illness and deaths with strikingly similar symptoms exhibited by horses within hours after giving quest on the Bogo page alone. Quite a coincidence. There is a saying in the horse world ” when you hear hoof beats, you don’t think zebra”


      • Not A Breed says:

        So, it looks like Zoetis removed their comment faster than it took to copy and paste the canned response in the first place.
        Luckily for my readers, I’m a God of WordPress, and can copy and paste too. ;)

        Their original comment, unedited.

        We read your blog post and wanted to reach out to offer some helpful information. It is important to us that you know how passionate we are about our customers and the animals in their care. At Zoetis, we adhere to strict safety and quality standards in everything we do. We take reports of adverse events seriously and promptly investigate and assess each case. All adverse event reports are submitted to the U.S. Food and Drug Administration in accordance with Regulatory requirements.

        Quest® has an 18-year record of safe and effective use since its approval in the U.S. in 1997. We carefully reviewed data from adverse event reports, and this has shown the safety record of Quest® remains consistent. Should you have any questions regarding Zoetis products, we invite you to contact our Veterinary Medical Information and Product Support Team directly at 1-888-963-8471.


    • Not A Breed says:


      Text from comment if you can’t see the whole thing:

      I lost 5 horses in 7 days while away at a horse show. I always fed feed through wormers, and we ran out without my approval the barn staff bought Quest and administered it to the horses left at home. I did have necropsy’s done on each one and it was all linked to the quest and causing neurological damage to each. Each horse displayed weaving of sorts, some colic type symptoms, some strangling type symptoms. Severe confusion, self-harm like throwing themselves into barn walls. frequent falling down if able to stand. these weren’t just our show horses, they were our kids, we raised all of them, pulled some through other illnesses and injuries. This has broken my heart and I have been away from horses since, it has been 2 years.


  • Lynn Cochran says:

    Thank You Not A Breed for helping to make people aware of the possible risk related to Quest. Bogo’s death will not be in vain


  • I deeply appreciate that this blog was sent to our rescue via email! It’s not worth the risk to the innocents coming in here for rehab.Though Quest is not our normal brand, we could have very easily purchased on sale and given once rehabs were at a specific weight. Your conclusions to anyone with common sense, raise an alarm bell. Thank you from Healing Horses “One child at a time” Inc., for this very important information!


  • shaiarabians says:

    brilliant blog post! I have been telling people about this for years!!


  • John says:

    Hi i was looking for death of foal after dewormer.we had a warmblood foal that was just weaned and a little calmer than usual treated by vet for worms with double dose of strongid. Foal died 24h after and giving dewormer. The liver was really white. I have never seen a white liver like that on autopsy. Could it be sign of poisoning ? Thanks


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

What’s this?

You are currently reading Quest, Quest Plus, Zoetis and a Horse Named BOGO at NotABreed.


%d bloggers like this: