What is the best supplement for gut health?

My horse that bloats with Any change in grass or hay gets yea sacc and just started happy tummy charcoal. Yea sacc has made his droppings more solid, bt he still looks bloated from autumn flush of grass - hoping the charcoal will help.
 
I started feeding brewers yeast when I saw it was the main ingredient in ermm some popular digestion supplements, and is far far cheaper.

I do also feed micronised linseed too.
 
I starting my skinny 5 year old on linseed too as well as brewers yeast

He is now blooming and shiny

Do I'm pleased with results, he will be staying in both of them.
 
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