First of all, I am no vet or expert on this matter but I can share what little I know and recently discovered. Our 14 year old mare Ripley has been cranky all her life (she is the horse in my avatar). That is how we met her and accepted her. We recently visited a trainer who claimed she has a problem in her hind gut which is highly acidic and that this can result in the development of ulcers..
As a remedy (in her situation) she advised to stop all store bought and prepared grain products as they actually contain stuff horses cannot digest, these product stay behind in the hind gut and become acidic and result in a so called hay gut... nothing to do with hay yes.
Her recommendation was to feed soy hull pellets, they contain virtually no sugars, an other one contributing to this acidic environment. Also add whole flax seed, not ground, it is digested to early in the system, they need to travel to the hind first. And add a table spoon of brewers yeast.
The other thing is your hay, alfalfa helps the digestion, I would not feed it on its own but you can buy good quality alfalfa/orchard grass mixes or alfalfa/timothy mixes. Find a supplier that has tested his hay, find one that is below 10% sugars.
Then the last thing is turnout, fall grass can have high sugar levels, specially in the morning hours after a cool night. I would limit turnout to about an hour and only in the afternoon when things have warmed up.
I swear in the two weeks we have been on the diet Ripley is feeling better. And Oh yes an other thing to test things by is the smell of a fresh turd, use a glove and break one open en take a good whiff, you can actually sense the sharpness being worse from one animal to the next.
Ripley diet as we feed her now:
1 cup soy hull pellets after turnout (pref before),
at 8 pm: 1 cup soy hull pellets, 3/4 cup alfalfa pellets, 2 tbsp whole flax seeds, 3/4 tbsp brewers yeast, vitamins and minerals, salt/ mineral block in stall.
Turnout 9/11 am, one pound orchard grass for lunch at 3 pm, One pound alfalfa plus one pound of orchard grass when put to bed at 8 pm
I hope this helps you and gives you something to start working with,
Matthijs.