What a wonderful plate!  Though we do not know the full history we have pieced together parts of it.  Brandywine Valley horse show purchased horse show awards from Garden Spot Badge Company.  The plate is pewter and was crafted by Old Mill ENT Lancaster, PA MilMetal.  Old Mill crafted many fine pewter plates over the years specializing in centenial and US historical plates as well as horse show awards.  We have not been able to date this though this is prior to the acquisition of Garden Spot Badge Company by Hodges Badge Company in 2014.   Approx 12" across