The size of it would about make a finger ring!

I’d guesstimate the length of that as 14cm, therefore the diameter would be 4.5ish cm. too big for a finger ring, unless it was worn by King Kong
Noooooo!
I'm not convinced that it is a horse head, maybe more like a ram or a deer? Looks like lead though.
I think the photo doesn't do it justice, but it's definitely a horse with a large ruffle/mane and a bit in its mouth. Also 100% not lead, it's too hard. You wouldn't be able to scratch it with a nail. I wonder if it was plated and the plating has worn off.