daf bit: Bechorot 23-24

[cellio]

The mishna teaches: R. Shimon ben Gamaliel says: if one buys an animal (from a gentile) that is suckling young, he need not fear that the young belongs to another animal. Why does this matter? Because when the animal he bought later gives birth, he needs to know if that offspring is a first-born male (which is subject to special laws). The g'mara on 24 has a long discussion of what is natural or unnatural in animal behavior and concludes that an animal that has never given birth does not suckle, so it must have given birth, and it's natural to assume that the animal it's suckling is its own. (23b-24)

(I think this last part, that the young is the mother's own offspring, is important only if the Jew buys both the mother and the young. In that case he would be subject to a torah prohibition against slaughtering them both on the same day. But if he only buys the mother I don't think this matters.)

Comments

[talvinamarich.livejournal.com]

Or, if the young that is suckling is male, then that is assumed to be the firstborn male and must be dealt with accordingly?

This leaves out the question: what if the animal is suckling a female calf/ewe? If the next animal born is male, must they assume it is the firstborn male? For all they know, that animal had another male offspring prior. From the tone here, I am guessing that you are supposed to assume it is first-born male lacking evidence to the contrary.

[chaos-wrangler.livejournal.com]

"First-born male" = first born + male, not the first male to be born, so if the first-born is female then it doesn't matter if a male is born later.

[cellio]

As chaos_wrangler said, the only concern here is that if you acquire an animal that has not yet given birth at all, and its first offspring is male, you then have special requirements. If it has ever given birth before you don't have to worry about that. Even if the animal it is suckling is a first-born male, if you aren't acquiring it there's no problem -- the gentile is under no obligation to bring the first-born male to a kohein. (If you do acquire the young as well, I'm not sure what the law is. I think I read somewhere that it's still not a problem because it wasn't owned by a Jew when it was born, but I could be wrong.)