May be eating my words now.
Found these.............(though none are the size of your horse)
"SONG DYNASTIES WHITE JADE RECUMBENT HORSE
Finely carved, Song dynasty white jade recumbent Horse ready to rise. Carving has surface ware with nice details. The heavy infiltrated Jade material is translucent, with extensive honey color inclusions.
Measures 4 1/2 inches 11.4 cm. Length"
"SHANG DYNASTY WHITE JADE RECUMBENT HORSE
Nicely carved, Shang Dynasty white calcified jade recumbent horse Carving has surface ware and good detail. The infiltrated Jade material is totally calcified. Measures 8 1/2 inches 21 cm.Length"
"SIX DYNASTIES CELADON JADE RECUMBENT HORSE
Finely carved, Six Dynasties Celadon jade recumbent Horse. Carving has surface ware with nice details. The heavy infiltrated Jade material is translucent, with white inclusions brown veins.
Measures 4 1/2 inches 11.43 cm. Length"
So I'm sure there are many more out there.
This last one, though different in style, appears similar in color to yours.
"SIX DYNASTIES CELADON JADE MYTHICAL HORSE .
Finely carved, Six Dynasties celadon jade mythical horse. The infiltrated Jade material is translucent with extensive brownish russet inclusions and veins. Sculpture has surface ware and is finely detailed with beautiful form. Measures 6 1/2 inches 16.3 cm length."
Now that I have proven I haven't got a clue about this I'll step away and let more knowledgeable folk chime in.