The number of animals in Jerusalem on Pesach is mind boggling. There was a requirement to bring a minimum of three animals as sacrifices. The first was the קרבן פסח that was partly offered on the מזבח and the remainder eaten at the Seder.
The second קרבן was called עולת ראיה, which was a burnt offering. The Torah says that we are not allowed to come empty handed. ולא תראו פני ריקם. The עולת ראיה was a sacrifice for being seen, ראיה, at the Temple Mount.
The third sacrifice was the קרבן חגיגה, or the Festival Sacrifice. There is a commandment to rejoice on the festival. The Rabbis say, אין שמחה אלא בבשר, there's no joy like the joy of eating meat. Part of this sacrifice was offered on the altar and the majority was eaten by the contributor.
Aside from these three sacrifices, people also offered sin offerings that they owed as well as שלמים, peace offerings. There were other sacrifices besides these.
So we can see, that there were an incredible amount of animals on the festivals. This is what Yechezkel meant when he said that in the future the desolate cities will again be filled with Jews equal to the number of cattle brought for sacrifices on the festivals.
Don't forget ספירת העומר. Yesterday was one!