How can I heal my horse?

From this post there are two solutions:

• Feeding the horse
• If the horse is registered at a stable and it dies, you can revive it with a Great Fairy

Feeding them will heal them at the same rate it heals you. An apple heals half a heart. I have no idea if boarding them helps, or how much max health is.

If it has been registered at a stable then if it dies you can resurrect him using a great fairy

This is the only source I found saying that feeding them actually heals them, so its credibility isn't the best. The Great Fairy option would probably be the best way to get your house back at full health.

Edit:

The information previously posted in my answer was from when the game was still fairly new. In fact, the source I have linked above is from only two days after the game released.

From a comment on my answer, this thread points out some ways to actually heal your horse. They are:

• Boarding the horse
• Fast-Traveling

The author of that thread even includes a YouTube video of them analyzing how horse healing works (see below). They concluded that feeding them does not actually heal the horse, as my answer said.

What the author does is damage their horse a set amount of times, and then tries various ways of healing it. After attempting to heal it, they see if the amount of damage the horse takes before collapsing is more or not.

Feeding them doesn't heal them, just increases bonding level. Boarding them heals them.

There is a fairy called something like "horse god fairy" Im not sure but i think you can ressurect horses from her.

You can find her at "Lake of the horse god-Horse god bridge- Fairy fountain following this bridge.

Said it would cost 1000 rupees to "start her up" and i didnt have that at the point but i belive the cost depends on how many fairy ponds you already activated.

Hope this helps and ill gladly try to answer if there is anything else about this.