Why do some horses eat sand or dirt

both of mine do and i want to know why. they have hay 24/7 and everything they should have salt, water, etc but they eat sand, thier poops aren't grity or anything but i'm wondering why they eat it.

I think there is a variety of reasons why horses and other animals eat dirt.

1) A lack of minerals or vitamins or salt can be one reason. Do you give your horses a mineral block or mineral suppliment of any sort? If not, you may want to try some and see if it helps.

2) Sometimes it is a habit, out of boredom. Last week someone wrote to ask what to do with their mini ponies that were kept in a stall alot, they were eating the wood shavings which was causing colic and other problems. So perhaps your horses are bored. I do know that my horses chew wooden fences in the winter much, much more than the summer. In the summer they spend most of their time grazing, in the winter they have spare time on their hands and seem to think chewing wood is a good way to pass the time.

3) Another reason is looking for probiotics. Probiotics are the natural flora and good bacteria that live in your intestines. You can buy horse probiotics through places that sell horse herbal medications or phamacuticals. Foals almost always eat horse manure, this is a way for them to build up good flora in their intestine. (Yes, it can have a downside and that is passing on worms and other parasites, but they do it anyhow) Also, in the wild horses will go to certain places and eat some dirt, it is high in probiotics. Horses that are kept in confined areas such as paddocks do not have access to this sort of dirt and sometimes will choose to eat sand and such as the next best thing.