This article examines a section in the Shuihudi 睡虎地 Rishu 日書 (Daybooks) entitled “Horses” (ma 馬) which describes the instructions for the performance of a ritual to propitiate a horse spirit. The text is one of the earliest transmitted ritual liturgies involving the treatment of animals. It reveals a hitherto little known aspect of the role of animals in early Chinese religion; namely, the ritual worship of tutelary animal spirits and the performance of sacrifices for the benefit of animals. Furthermore, it corroborates the existence of magico-religious rituals involving the treatment of animals, and demonstrates that cultic worship of animal spirits, criticized by some masters of philosophy, was part of the religious practices of the elite in the late Warring States and early imperial period. The article presents an annotated translation of the “Horses” section, discusses its contents and significance in relation to equine imagery documented in received sources, and examines its value as a source for the perception of animals and animal ritual in late Warring States and early imperial China.