Indeed Ivanov (1999), who has undertaken by far the most comprehensive study of the cognate terms for horse in Indo-European as well as the adjacent … - Vyacheslav Ivanov

The Indo-European homeland need not be identical to the area of horse domestication, but should be connected to it. The ways in which names and technical knowledge . . . spread should be explored.

The lack of a clear Proto-Indo-European word for 'donkey‘, given the presence of domesticated donkeys throughout most of the territory where horses were domesticated and where the Indo-European tribes must have lived, can be explained by assuming that *ekhwos was originally used with the meaning 'donkey‘ as well as 'wild horse; horse‘. ...[the PIE speakers lived in] Central and Eastern Asia, where paleozoological data show that the domesticated donkey is a recent introduction.

The Indo-European homeland need not be identical to the area of horse domestication, but should be connected to it. The ways in which names and technical knowledge . . . spread should be explored.

If horseback riding really did began at the turn of the IV mil. B.C. before the dispersal of Proto-Indo-European, it did not leave traces in the vocabulary of the later dialects. . . . Thus it cannot be proven that this type of ancient . . . horseback riding had originally been connected with Indo-Europeans.