Thanks guys! I'm waiting with the clean up of the cup until the archaeologists had a chance to look at it. I had to report it.
Don't think it's a plate for a horse, but rather a drinking cup or something similar. It's very nice decorated.
The mashed up thing under the horseshoe is also a cup, but I think more modern.
Either way, it's cool. And unexpected. The place belonged to a Swedish officer until the early 1900's.
Back then it was a huge farm!