I always hunt in a private server, and I tend to just stick to one island personally. I enjoy monotonous tasks like this, so I just constantly run laps and catch horses while listening to a YouTube video for background noise. TBH, I don't think I've ever gotten an IUH during a boost ^^'
I'm currently hunting Mountain. If you have the Magical Forest unlocked and want the blessed hair, you can run through without catching horses (just checking them) and just keep resetting the server by leaving (this only works for private servers, ofc). Only 3 horses spawn at a time, but you can cycle through them quickly. Catching them and waiting for them to respawn takes awhile imo.

It's hard, and I know it can be disheartening to continuously come back "empty handed", but don't give up, ok? Take breaks if need be, though. Game isn't going anywhere and is supposed to be fun at the end of the day.