Bechorot 19: How to Know that a Bechor is Truly the Firstborn of its Mother

Today's daf begins the third perek.  The rabbis analyze cases where we are not sure whether or not the mother animal has ever given birth before.  For example, when the animal was purchased from a Gentile, can we assume that the animal born is actually a firstborn?  Do we trust people we might not know as well; people who might not know about - or care about - our rules.

Today's Mishna shares two opinions:

• Rabbi Yishmael says that we decide based on the age of the animal
• if a goat gives birth in its first year of life, the offspring is certainly considered a firstborn.
• if a sheep gives birth during the first two years of life, the offspring is certainly considered a firstborn
• if a cow or donkey is three years old and gives birth, the offspring is certainly considered a firstborn

• Rabbi Akiva says that because certain types of miscarriages are considered to be 'firstborn', it is impossible to rely on Rabbi Yishmael's theory about the age of the animal determining whether or not its offspring might be its firstborn

The rabbis conclude that if we know that the animal has given birth once already, the new offspring will not be given to the kohen.  Secondly, if we know that it never gave birth before, the first offspring is given to the kohen.  Finally, if we are unsure whether or not it has given birth before, we wait until it develops a mum, a blemish, and then it can be eaten by the owner