This is actually a remnant of an old Japanese tradition which begun with the donations made by one of the first Emperors of Japan to the Kibune Shrine in Kyoto. During a rainy year, the Emperor's donation consisted in a white horse - as a prayer to stop the rain, while during a drought year the donation was a black horse, with prayers to bring the rain...
In time the tradition changed, replacing the real horse with a horse statue - and this is also the origin of the ema votive plaques, originally decorated with horse drawings.
EXIF info:
Nikon D90
Lens: 18-70mm F/3.5-4.5G
Focal Length: 70mm
Aperture: F/5.6
Shutter Speed: 1/40s
ISO Sensitivity: ISO 200