To be more precise, Madeleine Ravier referred to her invention as a "bicycle for animals." She did not restrict the design in her 1907 patent to horses.
Ravier concluded that, as human locomotion is more efficient on a bicycle, animals likewise benefit by an appropriately adapted vehicle. Weird Universe quotes a translation of her patent:
What man did for himself he can do it for animals, or at least for some of them; There is a way to increase the efficiency of their limbs by the intercalation, between these limbs and the field of motion, of mechanical devices receiving the reciprocating motion of the limbs, transforming it into continuous rotary motion, and ending in rotating parts; and the result obtained can be used to make animals move man faster and farther than has hitherto been done by using them.