This is possibly a work by the Chinese painter and calligrapher, Beihong Xu (1895 - 1953) who was known for this style of horse painting done with ink and brush. This assessment, however, does not stand as an authentication or verification of being a work by Beihong Xu. It is recommended to contact Christie's in Hong Kong to have the calligraphy deciphered. The estimate is based on actual recent past recorded auction sales of comparables by Beihong Xu. Retail 'asking prices' can be higher and vary.