An animal cannot be designated as a firstborn, rather, it has to be born that way. Similarly, it becomes a tithe by happening to come out as the tenth, when the owner counts them coming out of a coral. Therefore, when one designates exchanges for them, these exchanges cannot be brought on the Altar. However, they do acquire other qualities of the firstborn and the tithe: they are let to graze, and when they get a blemish, they can be eaten by their owner. In this they are different from regular sacrifices: upon getting a blemish, they need no redemption and can be eaten by the owner, but regular sacrifices remain sanctified and require redemption.
Another difference: the meat of the firstborn and tithe animals cannot be sold in a market, nor weighed out with weights, since this is degrading, and the owner has to take a loss on that. On the other hand, the meat of regular sacrifices that became blemished and were redeemed, can be sold in the market and weighed out in the regular way. This will fetch them a higher price, which is desired, because that money will be used to buy the next sacrifice.
Art: Pieter Aertsen - Market scene (detail)
Eruvin 62 – One who does not accept the laws of eruv
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