“mule.” It seems strange to see royalty, especially David and his sons, riding on mules since the mule is a crossbreed between a horse and donkey, and crossbreeding was against the Mosaic Law (Lev. 19:19). Nevertheless, the mule does seem to be the royal mount of choice at least during the time of David (no mule is mentioned in the Bible before David’s time; according to Judges 5:10, the wealthy rode on donkeys). David’s sons had them, as we see here, and Absalom rode one into battle (2 Sam. 18:9), and David had one (1 Kings 1:33, 38, 44). The mule was bigger than a donkey and sturdier on the steep hillsides and loose soil of Judea than a horse. It is possible the mules were not bred by the Jews, but imported (cp. 2 Chron. 9:24).
It may have been that since a mule is a sterile animal David was not concerned that they would breed and make more and thus infringe upon the Law. It may have been that David realized the practical value of the animal and kept them for that reason. We cannot be sure, but one thing is certain: no matter why David had them, he was not concerned about “setting a bad example” by having them.