TL;DR: Equine hybrids, other than the mule and hinny, have not been bred in any numbers nor received much attention and they did not achieve any prominence until Ewart’s telegony experiments at the turn of the century.
Abstract: Equine hybrids, other than the mule (ass ♂ × horse ♀) and hinny (horse ♂ × ass ♀), have not been bred in any numbers nor received much attention. The first record of a zebroid (ass ♂ × mountain zebra ♀) appears to be from Europe in 1782 (cited by Ewart, 1898). Then in the nineteenth century Captain Lugard recommended that “an attempt should be made to obtain zebra mules by horse or donkey mares, because he believed that such mules “would be found excessively hardy, and impervious to the (tsetse) fly, and to climatic diseases” (Ewart, 1896). However, the potential of the hybrids remained unexplored and they did not achieve any prominence until Ewart’s telegony experiments at the turn of the century. He coined the terms “zebrule,” “zebrinny,” “zebryle,” and “zebret,” in an effort to distinguish the zebroids he produced. Now many other terms would have to be added to cover the hybrids which have been recorded between three zebra species, two horse species, and the African and Asian asses (Antonins, 1951).