Kommentar zu Bekhorot 2:2

כל הקדשים שקדם מום קבוע להקדשן כו'. וכל שקדם הקדשן את מומן – these two clauses/sections, we explained above in Tractate Hullin [Chapter 10, Mishnah 2 and also Tractate Zevakhim, Chapter 9, Mishnah 3].

All consecrated animals whose permanent physical blemish preceded their consecration and were then redeemed:
Are subject to the law of the firstling and to the priestly gifts,
And when they become like hullin [by being redeemed] they may be shorn and may be put to work.
And their young and their milk are permitted after they have been redeemed.
And he who slaughtered them outside the sanctuary is not liable.
And they do not render what is substituted for them [holy].
And if they died they may be redeemed, except for the firstling and the tithe of cattle.
This mishnah and tomorrow’s mishnah are an exact replica of Hullin 10:2. They are brought here in Tractate Bekhorot because they have some rules concerning bekhorot. My commentary, including the following introduction, is the same as that found in Hullin.
An animal that has a permanent physical blemish cannot be sacrificed. Our mishnah distinguishes between cases where the blemish preceded the consecration of the animal, versus cases where the consecration preceded the blemish.
If the animal had a permanent blemish before it was consecrated, then the animal itself doesn’t become holy. Instead, the consecrator has in reality dedicated the value of the animal to the Temple. Thus this animal is treated like a hullin, non-sacred, animal, except that it has to be redeemed before any use can be made of it. If it gives birth to a firstling, the firstling is holy, as is the case with a hullin animal. When one slaughters it, he must give the shoulder, cheeks and stomach to the priest. After it becomes hullin by being redeemed, it may be shorn and work may be performed with it. Similarly, its young and its milk are not prohibited. One who slaughters it outside the Temple is not liable for he has slaughtered a non-sacred animal. If one tries to exchange it for another animal, the other animal is not holy. If the animal dies, it will still need to be redeemed, so that its meat can be given to dogs.
The only exception to all of these rules is if this animal that had a permanent blemish is itself a firstling or a tithed animal. The firstling is holy from the moment it is born even if it has a blemish. Similarly, even blemished animals must be tithed (see Leviticus 27:33). Thus these animals are holy regardless of whether they have blemishes and therefore they cannot be treated as the animals above were treated.