Why is a ram without blemish used for the guilt offering?
N.B: Unlike the bulls, goats and lambs used for sin offerings, the ram is not required to be young only that it be without blemish.
Lev 6:6 (KJV) And he shall bring his trespass offering unto the LORD, a ram without blemish out of the flock, with thy estimation, for a trespass offering, unto the priest:
Why not use a bull or goat to atone for the sin of trespass? Why is the ram required to the exclusion of other animals for this offering?