Adam Clarke on Psalms 69:31

An ox or bullock that hath horns and hoofs - Oxen offered in sacrifice had their horns and hoofs gilded; and the psalmist might mention these parts of the victim more particularly, because they were more conspicuous. Others think that full-grown animals are intended, those that had perfect horns, in opposition to calves or steers. I think the first the preferable sense; for the horns, etc., of consecrated animals are thus ornamented in the east to the present day.