(R. Yochanan): They decreed against buying a female blemished animal with Ma'aser Sheni money, lest it's offspring be used for a sacrifice (thereby causing Ma'aser Sheni not to be consumed, as its Eimorim will be burned on the altar). And they also decreed against buying a male blemished animal on account of a female blemished animal.

(Said in the name of R. Yochanan): They also made the decree against buying an unblemished animal to consume, as the Baraisa teaches...

Originally they would say that (with Ma'aser Sheni money) one may buy an animal to consume (even though it is a Mitzvah to buy for a Shelamim offering). Everyone was buying animals for consumption rather than to be used for Shelamim offerings. They then said that one may not even buy a beast or a bird (for consumption).

It's like the Baraisa that taught - Both Sheviis and Ma'aser Sheni money may have their Kedushah transferred onto a female blemished animal or onto another animal, bird or beast, whether alive or slaughtered. These are the words of R. Meir, but the Chachamim said that one may only redeem onto slaughtered animals.

(R. Yirmiyah citing R. Shmuel bar Rav Yitzchak): They decreed that they should only buy slaughtered animals so that they shouldn't hold onto them and breed flocks from them.

R. Yirmiyah met up with R. Zeira and R. Zeira said to him, "R. Shmuel bar Rav Yitzchak is still alive and you are hanging rags on him!'' (You are quoting him as saying something with baseless reasoning, as that was not the reason for their decree.) "As they say in the name of R. Yochanan that they even decreed about an unblemished animal (where breeding flocks is not relevant)''.

(R. Yirmiyah to R. Zeira): Perhaps that reason was said about Sheviis (where avoiding bringing it as a sacrifice is not relevant).

They discovered a Baraisa that taught that it was in fact said about Sheviis.