Humans settle on a planet and use alien beasts instead of machinery. The beasts are in fact sentient and a contract is negotiated to allow the humans to use the aliens. I vaguely remember that there was some conflict around this, as there was an alien faction that refused entering the contract.
Part of the adaptation that the aliens need to undergo involved "sewing" a sap/feed bag onto them (this left quite an impression on my young mind, so I am quite sure of this plot point). Another vivid impression is that the "contracted" aliens that served as vehicles could be put into "idle" mode with an ignition key, similar to an automobile.
I probably read the story in the late 70's, but it had a 50's vibe to it -- can't really define it, possibly a cold-war human-chauvinistic feel). It was kind of a Blish ("Surface Tension") or Campbell ("Who Goes There") style, if that makes sense.