Adam Clarke on Job 6:5

Doth the wild ass - פרא pere, translated onager, by the Vulgate, from the ονος αγριος of the Septuagint, which we properly enough, translate wild ass. It is the same with the tame ass; only in a wild state it grows to a larger size, is stronger, and more fleet. The meaning of Job appears to be this: You condemn me for complaining; do I complain without a cause? The wild ass will not bray, and the ox will not low, unless in want. If they have plenty of provender, they are silent. Were I at rest, at ease, and happy, I would not complain.