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Another Diarrhea Post


Hello COTH. I am here to pick your brain…I have searched these forums and read everyone’s suggestions about diarrhea in horses.

I have a 27 year old warmblood gelding with no significant health problems who has had chronic intermittent diarrhea for the past 8 years. In the last year, the diarrhea has worsened in severity and frequency and can range from cow patty loose to firehose liquid poop. Metronidazole would clear it up, and it would return once the Metronidazole was discontinued. For 8 months, the diarrhea was completely controlled with Assure Guard Gold on the loading dose. I tried to taper to the maintenance dose and the diarrhea would return, so we kept him at loading dose and it was worth the fortune Assure Guard Gold costs to have a diarrhea free horse.

The Assure Guard Gold stopped working this summer and we went through the Metronidazole song and dance again. Of course, the Metronidazole clears it up, he stops it, it comes back. For a few months, the vet transitioned to Metronidazole as a spot treatment. Horse develops diarrhea, give Metronidazole. Discontinue as soon as diarrhea resolves. Wait to give Metronidazole until diarrhea develops again. Metronidazole works beautifully—Within 1 to 2 doses, he is back to normal and typically can last 10 days before needing another spot treatment. However, a few weeks ago, he developed firehose diarrhea, had an episode of mild colic that required a vet visit, and had persistent firehose diarrhea following. We reintroduced the Metronidazole, poop cleared right back up, left him on it for a few days longer since he had just had the colic episode, and then discontinued the Metronidazole. This time diarrhea returned within 2 days of discontinuing the antibiotic after normal, perfect poop in the AM and liquid cow patty poop in the PM. Today, we started with liquid sloppy poop and then 20 min later after getting out and moving his legs in the arena, he had a solid sort of normal small volume poop, then back to liquid sloppy cow patties the rest of the AM. His legs are a mess. His tail is a mess. He’s a stinky poopy mess. This is not fecal water syndrome to be clear.

He has seen the dentist who feels he has adequate grinding surface still. The vet sent out extensive stool studies that just returned. He says everything was normal. I have not seen them and have not had the opportunity to ask more questions on exactly what was tested. I know no values were reported on the bacteriology studies, but there was no Salmonella or C. perfringens. Just Enteric bacteria and E. coli were noted, which I know is typical in a normal horse. He was supposed to check for parasites as well… I will call Monday to get the other reports to see exactly what was tested. Unfortunately, I am often unable to answer the phone, so my mom is who gets the calls and doesn’t always know the questions to ask. I do not believe he has had any stool studies done specific to IBD. Definitely no ultrasound has been done.

He eats alfalfa, coastal hay, and a ration balancer. We are actually going to transition him to senior feed as the diarrhea and winter do cause weight loss and he would benefit from more groceries. He’s on Equioxx and Sucralfate daily. Aside from the colic episode the other week, he is generally unbothered. He is on well water, but it seems that the stool studies are all normal. The vet said potentially it could be the E. coli and suggested trying another 10 day course of Metronidazole and then treatment with Doxycycline. My gut is telling me this is not the right move— I am hesitant about the amount of Metronidazole this horse has been on, and I am concerned with hitting him with another antibiotic that could worsen his natural flora and complicate his diarrhea. It just doesn’t feel like the right move to me and like we’re poking around with a stick in the dark.

My differentials include:
IBD or some sort of mild colitis from long stem forage in an older horse
NSAID induced ulcers leading to diarrhea
Food sensitivity
Absolutely no good reason with no great solution leading to lots of stress and $$$ spent by his mother

Any thoughts would be greatly appreciated!! We’ve done the probiotics, we’ve done the Assure Guard Gold, we’ve done the bio sponge. If it exists, we’ve probably tried it. Thanks in advance!

I would enlist a good PhD nutritionist to work with your vet. The likes of Dr Rachel Mottet and Dr Clair Thunes would be excellent resources


I had a 2yo at my farm for 2 years that had pretty consistent diarrhea from the time he was a foal. After doing all of the things you’re doing, I finally convinced the owner to allergy test. He’s allergic to carrots. Owner had been coming out 3x a week to feed him carrots. :roll_eyes:

Obviously stopped the carrots, but we think he was still sensitive to grass, so the diarrhea continued. A metric F ton of biosponge and omprazole, plus putting him on a dry lot (after he left my farm) helped him a lot.

I’d say allergy test him. Good luck! Washing butts and tails everyday is no fun (horse at my farm was a medicine hat paint🙄). I’d also recommend a braid-in tail bag (the kind made out of lycra horse jammies material), that helped a lot keeping the mess to a minimum.

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Allergy or food sensitivity sounds possible. I have a 22 yr old stallion who cannot tolerate alfalfa - will immediately get runny butt. His is not full fledged diarrhea, more like fecal water - poop then squirt.
Took a while to figure this out. He’s now on timothy hay only, and his senior feed. For some years was on a T/A mix hay, then one day it just hit him. Did the metro thing, it worked well, would have issues 1-2x per year. Then they got more frequent, switched his hay to just timothy on a whim after one metro course and all was well.


I had two horses with constant diarrhea, but a third one that was fine. All three horses had the same feed and water, and they all lived together outside with run in sheds available. I tried everything the vet could suggest, including Pepto Bismal. You can imagine how that looked on a light gray horse that was trying to refuse the syringe. I had a pink pony. Biosponge worked for a while, then didn’t. What finally stopped it in both horses (by the way, the other was a Paint with white stockings, of course) was Purina Strategy added to their daily Purina Senior. I was so happy to stop having to wash butts and tails, especially in Colorado winters.

They also ate alfalfa/grass hay mix. The Paint gummed it but mostly got the Senior/Strategy mix, while the light gray pony still had all his teeth. My other pony (who didn’t have diarrhea) also gummed the hay while mostly living on the Senior/Strategy mix.



Know that blood testing for food allergies is highly unreliable in horses. If you get a hit coming up towards 1000, then you can really consider that an allergy. But most horses have some to a lot of hits in the 100s and 200s, which are not allergies. Flax and oats almost always get a hit with Nextmune test, it’s a pretty well known issue with their test.

So you COULD try that to see what’s what, see if there are any legit allergy hits.

But, if you don’t have that level, but get a lot of 100-300 or so ranges of hits, then consider leaky gut is the root issues, and go from there, which is why I recommend a nutritionist (a real one!) to help work through the diet and supplement issues.


I had a horse with persistent cow patty poop and went through All The Things without much result. What finally fixed her was a move out of state. It was pretty wild–from the moment she came off the trailer, she was fine, and her poop was normal from that point forward.

That’s not feasible for most (and it’s certainly not like the move was an attempt to solve her issue) but in retrospect, I really wondered if there was a low level bacterial contaminant in the well water. Something that most horses tolerated fine, but she did not.

Perhaps something worth investigating for your guy.


Metronidazole is a standard first line treatment for C. Diff colitis… But the patient relapses after being taken off the drug. Not saying this is the case, but C Diff is difficult to detect unless you test specifically for it.

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Have you tried plain yoghurt or probiotics?


" Although metronidazole is reportedly safe to use in equine patients, the horses in this study appeared to develop early indications of colitis despite having normal feces. AAD is poorly defined in the veterinary literature in regards to the number or character of abnormal stools, but is generally regarded as a temporal association with the initiation or discontinuation of an antimicrobial agent and the development of diarrhea [9]. While diarrhea is characteristically considered pathognomonic for colitis, most horses exhibit prodromal symptoms associated with the gastrointestinal tract before diarrhea is clinically manifested. These symptoms often include inappetance, malaise, fever, and behavioral expressions of abdominal pain that precede the development of diarrhea. The clinical impression is that AAD is often acute in onset, occurring rapidly after the initiation of antimicrobial therapy. In horses, one study reported that the average time for development of diarrhea was 3.4 days after antibiotic administration (range: 1-11days) [36]. In humans, there is also evidence for the development of diarrhea associated with antibiotic discontinuation. This may have played a role in the death of Horse 3 on Day 14.

In this study, metronidazole decreased the diversity and altered the bacterial composition of cecal content and fecal samples. Subsequent functional alterations of the microbiome were reflected in the metabolite profile of the fecal samples. The timing of these changes coincides with the development of symptoms of GIT disease in these horses. Antibiotic administration, including metronidazole, is recognized as a risk factor for the development of diarrhea in species, such as humans, dogs, cats, and horses"


I’m so sorry you’re dealing with this, I’ve had to deal with FFWS in my horse and it is awful.

Out of curiosity, have you tried changing his hay? I know that diarrhea and FFWS are different, but in my extensive reading on horse poop this past year, forage type seems to be a common factor in irritated guts.

On that note, I agree with the suggestion to speak with a nutritionist.

Another thought: what is the ration balancer that he gets? I wonder if he could have developed a sensitivity to something in it, if he has been on it this whole time.

Genuinely wishing you success in resolving this as I know how awful poopy bums are :sweat_smile:


I probably would change hay to something completely different. Alternatively, try a complete pelleted feed like alfalfa or Timothy pellets. I’ve seen older horses with diarrhea that resolves when changing to a pelleted feed.

You could try something like Biosponge if this is Clostridia related.

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First, thank you to everyone for the responses thus far! It is nice to hear that I am not alone, although I wouldn’t wish this on anyone! He had a total firehose watery diarrhea blowout in the crossties this AM. I still w/t/c him and on Sundays, we do a leisurely stroll around the ring for an hour or so. He had a small amount of completely unformed liquid poop when we first got up there, and then towards the end of our walk, he had a small amount of more normal-ish but still not super formed poop. The spectrum of poop that is displayed in this horse during a week period is pretty impressive. Like I said, the metronidazole clears it up completely, and he is usually perfect for about 7-10 days without after 2-3 doses of it. Then he starts to get loose again. He goes out all night and is in during the day, but he historically gets loose poop if he doesn’t go out all night. I wonder if movement has something to do with it.

I am actually going to move him in a week to a place where he can be out moving around 24/7. We will see if a change in setting and water (not well) makes a difference @Simkie . They feed timothy and alfalfa vs the coastal and alfalfa he is currently getting. Whether or not we switch to pellets vs timothy will depend on what the nutritionist feels—I am meeting with them this week (thanks @JB @4horses ). His ration balancer is of poor quality and he gets a hefty amount of it. I have not had a ton of freedom to change things due to his current living situation, so I am looking forward to switching him to a senior feed and off the ration balancer to see if potentially that is contributing to the problem and his overall body condition @BayBondGirl . He’s currently a 4—the diarrhea and the cold just doesn’t work for him.

@Equibrit regarding the metronidazole, that is an interesting point. It is odd how the metronidazole immediately clears up the diarrhea, and then slowly it will return. He is on probiotics daily with the assure guard gold. We also have supplemented with Probios and Full Bucket to no avail. He definitely developed diarrhea before metronidazlole was first introduced to him last year, but like I said—it never has permanently fixed his problems. I am definitely hesitant about the metronidazole and would prefer not to have him on antibiotics. I worry it is doing more harm than good in the long run as we disrupt his normal microbiome. I do wonder if a fecal transfer is something to consider in the future though I know the safety and efficacy is not widely studied.

Thanks to all again for the input thus far!

One last note: This horse is out of dry lot 12 hours a day and gets around 1 hour of grass per day via hand grazing. We are in the south, but it is winter time technically… I don’t think that the pastures have that much grass… When I move him, what are your thoughts about transitioning him? He will off grass after rain for a day to rest the pasture, but I don’t have any knowledge or experience with transitioning horses out like this.

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Not to make light of the situation, but only horse people would be discussing a “spectrum of poop”.

What balancer is he getting out of curiosity? Most have a maximum recommended feeding of rate of 3 lbs/day and that’s for growing or very hardworking, easy keeping horses.

I think using a complete type of senior feed with lots of forage built in to it will be a good place to start, as well as the hay change. I’ve seen it a couple of times with seniors that a combination of teeth starting to wear (even if still decent) and a harder time digesting long stemmed forage improve with a change to a complete (forage included) feed and /or replacing most of the forage with a soaked hay pellet or cube. Sometimes they manage fresh grass well but just can’t transition to mostly hay.


I have a 23 y/o gelding who has trouble with diarrhea and sometimes free fecal water. I did consult with a nutritionist and we took him almost completely off of hay and onto Timothy pellets and a complete senior feed and his diarrhea completely resolved. That required 4 feedings a day, so not really a long term solution for him. But it did tell me that hay is definitely the problem. This horse does very well during the summer, when he gets less hay and more grass. Winter is when he really struggles.

Here is what works for my horse:

The best hay for him is a soft orchard. Stalky hay is a definite no-no.

He gets 2 pounds of Timothy pellets a day and 2 pounds of complete Senior feed a day during the winter. In summer we can cut this back. He does also get a ration balancer year round.


If he is not used to grass introduce it slowly like you would do with any change of feed.

Reading forums anecdotally that say try bananas. Also pollard.

Personally diarrhoea is better than a horse who suffers from constipation, so be careful you don’t go the other way.

Reading through I think changing the water and the feed, one at a time from science perspective, is the way to go.


How much psyllium is in the loading dose of the Assure Guard Gold? I ask because my mare has free fecal water, which I know is different, but I’m wondering if you could experiment with more psyllium like some do for the FFW.

My girl does fine in the summer when she’s on grass 10 hours a day, but now that the grass is mostly gone her FFW is returning. I keep her in check with about 1/4 to 1/3 cup pure psyllium husk powder with breakfast and dinner. I know this doesn’t work for everyone but since the AGG worked before, and it’s primary ingredient is psyllium, I’m wondering if he just needs more than even in the loading dose of the AGG. Dr. Mellon has an article that says you can give up to two cups per day of the pure psyllium husk powder.

I used to buy it in bulk from Uckele but now that SmartPak owns them it doesn’t seem to be available any longer. I wonder if Mad Barn might come out with it now that Dr.Kellon is with them.


I’m going to suggest two things I have seen work:

Stop putting water in the big water trough and hang buckets in the field and clean them every day. If the diarrhea cleans up replace the tub, let the old one completely dry and don’t use it again for 6 months. Some of the plastics became uncleanable and can harbor all kinds of stuff.

Switch hay that has definitely not been sprayed with Grazon or any other persistent broad leaf herbicide. Some horses cannot tolerate the residue.


Another idea.


Thanks again everyone for the replies! He is going to be moving this weekend. Funny… the firehose diarrhea got so bad, I started him back on the metronidazole Sunday night. On Tuesday PM, he still had complete liquid (like straight water) diarrhea. By Wednesday AM, he was back to completely normal poop. He has been normal since, but I have left him on the Metro. I will pull him off a few days post-transition and see what we get. Pretty wild how well the Metro works for whatever is going on with his insides where he can be night and day within 12 hours.

@WNT His ration balancer is trash. He will be slowly transitioned to Triple Crown Senior beginning next week. Hoping for some good luck

@stb Pellets will definitely be the next step after our transition from coastal to timothy and feed change + 24/7 turnout if the diarrhea persists. Thank you for the suggestions. We will see where we end up!

@Pico_Banana No way of knowing how much is in the Assure Guard Gold. I will look into Psyllium husk as a solution if he continues to have diarrhea despite all the dietary changes! Assure Guard Gold is mad expensive, and it didn’t work for him at all.

@Amberley Thank you for the suggestion! I guess we will have a mini experiment re: water buckets/trough since he is moving. I am curious if well water has something to do with it. We will see. Interesting about the Grazon. I will keep that in mind.

@Equibrit Funny that you mention this… per nutritionist recommendation, I have just started him on RiteTrac which has EquiShure in it. He seems to like it! Also using Platinum Balance for probiotics. We will see how it goes!

Anyone have any thoughts why the Metronidazole seems to be this magic cure all the time? I notice that if I don’t give him the metronidazole as soon as he starts a flare, that it will take much longer for the metro to take effect. Previously, I would give it to him within 12 hours of him showing symptoms, and it would resolve the next day. I tried to avoid putting him on another dose of antibiotics this time around, and it took 3 days to resolve. He must be so inflamed and irritated that it takes time for his gut to cool off. Thanks again to all. Put some good vibes into the universe for his move this weekend. This horse hasn’t lived anywhere else other than here for almost his entire life. I keep telling myself it’s like he’s going to a horse show. He might be old, but he was a show horse for the majority of his younger years, so I hope he will tolerate the move alright.


Most likely he has some kind of bacterial or parasitic infection that isn’t clearing or he’s constantly getting reinfected. Did you test for giardia?