Chronic cow pie/loose manure?

Note: This post concerns a friend’s horse and I am trying to provide as much detail as possible.

My friend has had this smaller paint gelding since it was a foal and is 8 years old now. This problem only started a few years ago. When the horse starts pooping it is a cow pie but at the end there is a few solid pieces. 4 different vets have looked at the horse and can’t find anything wrong. A stool sample was sent in and they found nothing wrong. He put the horse on probiotics for 5 months but nothing changed. As far as I know they deworm him too. Also, switched up the diet to see if anything was upsetting his gut but again nothing changed.

Is there any problems that wouldn’t show up on a stool sample test? I’m curious as to what started this?

If @Risk-Averse Rider (or maybe @Risk-Averse Rider 2 ?) is still around, I believe she has a horse with a similar problem and may have some advice.

Ask vet for bottle of metronidazole tablets.
Meanwhile clean all water containers with bleach
have well water and any pond or rain water analyzed by your county ag agent
if you have sandy soil buy psyllium pellets and give monthly as directed. Smart pak sells them.

My old guy is like this. He gets half the big scoop of biosponge in his dinner nightly. My vet approved this regimen and he has been right as rain.

I have a gelding that gets chronic diarrhea if he eats orchard hay.

My 18 year old BSP has had this same issue since I got him 11 years ago. BioSponge does make the poop normal, but since he is in good flesh (fat), I generally leave him alone to poop how he pleases. He has a beautiful coat, looks very healthy, and as I said, maintains his weight on a handful of grain.

I went through this with one of mine, and tried a laundry list of cures. Nothing worked. Finally gave up, since it didn’t seem to bother her.

When we moved across the country, it cleared up overnight, never to return. Wasn’t the hay–I’d brought some with me. Best guess is there was a low level bacterial contaminant in the well water that most tolerated and she did not.

If you’re not able to clear it up with the standard stuff–biosponge, treating hind gut ulcers, playing around with his diet, antibiotics, etc–consider testing his water.