A bechor [first born] of a kosher animal is a korban. If it gets a blemish, it can be eaten not as a korban. Chazal said you must have an expert to declare that it is a real blemish.

A bechor that fell in a pit R’ Yehuda says an expert should go down in the pit and see if there is a blemish and if there is a blemish, it should be taken up and slaughtered. R’ Shimon says if the blemish was not known before Yom Tov, the animal cannot be slaughtered as it is muktza.

Beitzah 3:5

An animal that died on Yom Tov is muktza. A story is told about this. They asked R’ Tarfon about this and about challah that became tamai and cannot be eaten. He said they both cannot be moved since they are muktza.