This is a simple plugin that I was requested for. Just putting it out there for all those who might want the same thing.
This plugin increases the average health that horses have. The config has an option to enter the new average horse health that you prefer. You can set it to double or triple the present value to increase the average horse health by that much.
All horses that spawn will have their health spread around this new average.
No commands, no permissions. Just drag and drop. Start the server, edit the config and restart the server.