My first suggestion was possible sand, and you have to take in account that it is not always detected in that poop test
Sand Colic in Horses | TheHorse.com

From the link below, you will see that you need to repeat that sand test several times, for accuracy, then if still negative, consider other factors

Easy Sand Test - Your Best Defense Against Sand Colic

Do you give the horse a lot of Magnesium oxalate,as it can cause loose stools.
You might try some probiotics

Here is a good article, which might help you pin point the cause, or at least give you other avenues to explore

What Does Your Horse's Stool Say? | TheHorse.com

 

I have had this problem chronically with one of my horses. First thing I will say is that a tail bag makes clean up far easier. I live in a very cold climate so baths are not an option this time of year. I got tired of picking manure out of his tail. A tail bag solved the problem.

The next thing I would try is a probiotic. Not sure what those Smart Paks contain, but you should be able to get some kind of probiotic. You may have to play with the dosage (within reason of course). Some horses respond better to a half dose, some to a full.

My vet also recommended I feed second cut hay rather than first cut, which is more fibrous.

All of these things did not completely resolve my horse's loose stool, but it helped. Someone also recommended psyllium to firm up his stool. I haven't tried that yet because I am seeing gradual improvement. But that's something else to consider.

 

Here are the ingredients in the Smart Paks:
Corn Distillers Dried Grains with Solubles, Heat Stabilized Rice Bran, Active Dry Yeast, Dried Whey, Yeast Extract, Brewers Dried Yeast, Fructooligosaccharide, Fenugreek Seed, Linseed Meal, Dried Aspergillus niger Fermentation Extract, Vegetable Oil, Dried Lactobacillus acidophilus Fermentation Product, Maltodextrins, Dried Enterococcus faecium Fermentation Product, Salt, Dried Bacillus subtilis Fermentation Product, Dried Enterococcus lactis Fermentation Product, Dried Aspergillus oryzae Fermentation Extract, Coconut Oil, Vitamin E Supplement, Natural & Artificial Flavor, Citric Acid (Preservative).

He gets one maintenance dose, roughly 1/4 cup.

 

Yes, those ingredients are similar to what is in the one I used. It worked fine to get rid of nervous runny stool when my mare first came to us, but with my gelding, who, like yours, ranges from normal, firm stool, to runny, it hasn't made a difference.

I agree with Smilie, that finding the cause is best. However, if you're like me, and you're still scratching your head after trying everything, psyllium might be a solution. Meantime, get a tailbag on him asap!

 

I did braid the bottom part down to help keep it out of the way, but that could be helpful! His butt is what gets the most dirty though

 

I will brush off any dry bits, or use baby wipes to clean the wet stuff of his but and hocks. But it has made a big difference to put the tail in a bag.

I sympathize with you. We have dealt with it for a while now, and I've given up for now because we're dealing with a cough and trying several meds for that so not a good time to try to get his stool to be consistently firm. And it's mind boggling because sometimes he will go for days with solid poop, then suddenly, it gets runny again for no apparent reason.

A lot of people have told me this is probably just how he is. However, it only happens in the winter, not when he's grazing in the pasture.

 

more info:
'Both large and small strongyles have been incriminated as a cause of chronic diarrhea in horses and foals. The condition associated with small strongyles in horses is termed cyathomostomiasis and has been reported to result in recurrent colic, diarrhea, and weight loss.'

So, if you never have used Quest as a de-wormer, I would try that

http://www.merckvetmanual.com/diges...m/intestinal-diseases-in-horses-and-foals/parasitism-gastrointestinal-in-horses

 

more info:
'Both large and small strongyles have been incriminated as a cause of chronic diarrhea in horses and foals. The condition associated with small strongyles in horses is termed cyathomostomiasis and has been reported to result in recurrent colic, diarrhea, and weight loss.'

So, if you never have used Quest as a de-wormer, I would try that

Parasitism (Gastrointestinal) in Horses - Digestive System - Veterinary Manual

I know this is meant for the OP, but just for the sake of information, I did try Quest on Harley, but it didn't change anything. Still has chronic on and off loose stool. The OP should rule it out, however, but it doesn't always work, because the problem is not necessarily parasitic in nature.

 

I would get a fecal exam (collect poo and send in for a vet to put under a microscope). Are you rotating wormers? They are intended to cover different things, so it's important to use the right one. I would look into a round of dosing with ProBios (Dispersible Powder 5 lb for Equine | Probios) or using the Dac Digestive Aid (Digestive Feed Additive "DDA" 20lb | dac® Direct Action Company) which did wonders for my gelding (it includes ProBios, yeast, and other gut-health-goodies) who came to me terribly dehydrated and colicy from loose poo and had no luck with wormers, plain pro bios, Digest 911, yeast supplements, or even two types of gut-booster from the vet! Dac's digestive aid made a difference in about 2 weeks, and after a month with normal stools I took it out of his diet and his poos remained normal: It fixed his gut balance, not just put a band-aid on it. Some products will 'work' but then once you take them away, the loose poo comes back. So watch out for the 'band-aid' products. Keep us updated

 

My vet does periodic stool sample testings and gives wormer only if they find worms so that he doesn't become immune to the wormer.

 

When was the last time his teeth were floated ? Try some bran , make it a mash , but not a super wet mash. You could also try a product called bio sponge. it helps to remove toxins etc from the gut.
You could try the safe guard, wait 3 days, dose, wait 3 days dose . I had to do this for two weeks on a draft mare, and she finally pooped out a rather large worm, baby snake lol.. I then waited 3 days and dosed her again .

 

He was floated about 6 months ago since I noticed he was dropping a lot of his hay and that seemed to fix it, so his teeth should be ok.

 

I have the same problem with my horse. In the past, it was a consistent Fall event. And my horse and one other one (out of a herd of 6) would get the runny stool, but the other 4 would be fine. The other owner and I put our horses on probiotics (the same Smartpak formula that you're using). I honestly cannot say that it (the probiotics) did anything. Eventually the loose stool problem resolved itself for both horses, but we think the Fall event is caused by eating dried leaves. So it might have been that the loose stool resolved itself when the leaves blew away more than that the probiotic helped.

My horse was fine this Fall. Ha! Now suddenly in the dead of winter, he has the issue again. He's on probiotics, because he's now on a supplement bundle (cheaper for my situation) and the probiotics are in it automatically. So I have no real way to judge the performance of the probiotics (e.g., perhaps this would be worse if he were not taking the probiotics?).

Anyway, my vet says not to worry about it. You also do not seem worried. Simply the maintenance of cleaning the horse gets old. I get it! My vet did recommend this product
Bio-Sponge for Horses | Equine Gastrointestinal Support

It's called biosponge. I never did get any of it. (and now I'd need to do some research to see if it would interfere with his supplement bundle). Nevertheless, you may want to give it a try. My take is that it's more like a fiber product that just firms up the stool.

Best of luck.

Arcadianartists -- thanks for the tip about the tail bag. I had not thought of that. To be honest, I mainly just ignore it. I don't ride in the winter (because I'm a wimp). I cannot bathe him in the winter, because it's cold. So I just groom him normally and don't get too concerned about it.

 

I would also like to somehow add more fiber to his diet and see if that does anything. I'm boarding but (not seriously) looking for a new place that has better pastures for a better deal, so I can't do a whole lot about the hay situation (and I can't afford my own) but I might be able to get it in supplements... Idk I will look into it some more.

 

Ha! I think that stevenson and I were posting at the exact same time about BioSponge. Funny.