How much dirt does a horse eat when it is daily grazing?
Eating dirt is perfectly natural although most people will say it is lack of minerals or salt.
I have noticed many times thee things.
The first is that when a horse is injured and has to stay in the stable for a period of time, if you throw it in a tussock of grass with roots and dirt still attached, there will only be stones left, they will eat the dirt.
Secondly, horses that spend a lot of time in the stables with no turn out, when given the chance to graze in hand, will eat grass but will start to lick or bite the soil.
Finally, horses that are continuously stabled will often be very loose in their droppings, give them the tussock of earth and their droppings are fine.
My conclusion is that horses need a certain amount of dirt in their diet.