I had to search about and it's indeed a lot:

"it is quite normal for a horse to poo (defecate) 8-12 times a day and produce anywhere from 13 to 23 kilograms of poo a day."

Source: https://www.ranvet.com.au/horse-poo/

https://en.wikipedia.org/wiki/Great_horse_manure_crisis_of_1...

That's what you get when your primary source of nutrition is very calorie-poor and largely indigestible.