Oh, and there's a big debate on the type of salt you feed (in case our lives weren't complicated enough). Salt licks generally do not provide enough. Horse tongues are not rough, like cows, so they don't get enough off the block. Which is why I use loose salt in a pan by their water trough. Some people use table salt, but it's iodized. Some people think that's good, some people think it's bad. Iodine is necessary for good thyroid function, but in trace amounts generally already available in forage. There are also anti-caking agents in table salt. The more you read about it, the more you start thinking it has a lot of additives for straight salt. Some people will use sea salt (benefits of this remain to be proven), some use Himalayan salt (this one contains a lot of minerals, some good, some maybe not so much - for me, not a good choice, since it contains iron). I have personally settled on kosher salt flakes. No anti-caking agents, no iodine, just straight, boring salt.
There is also loose livestock salt (like Redmond salt), but again, I avoid anything that contains minerals other than salt because I already have their exact requirements measured out precisely and added to their hay cubes. I don't want to add anything to the equation.