Rif Beitza 3b {Beitza 6a continues; 7a}

{Beitza 6a continues}
of Rosh haShana {and it was the first day}. He {Ravina} saw that he {Rav Ashi} was sad. He said to him: Why are you sad?
He said to him: For I did not establish an eruv tavshilin {to cook from Yom Tov to Shabbat, which was the day after the second day of Rosh haShana}.
He {Ravina} said: So let Master establish one now {on Thursday}! For did not Rava state that one may establish an eruv tavshilin from one day of Yom Tov for the next and make a condition {namely: if today is indeed kodesh, then there is no need for an eruv, for Friday, erev Shabbat, is chol; and if today is chol and tomorrow is kodesh, then this is establishing an eruv tavshilin from before the actual day of Yom Tov, which would be effective to permit cooking from Yom Tov on Friday for Shabbat}.
He {Rav Ashi} said to him: One may say that Rava stated this about the two days of Yom Tov of the exile. But regarding the two days of Yom Tov of Rosh haShana, would he say?!
He {Ravina} said to him: But the Nehardeans say, even by an egg!

{That is, regarding what Rava said earlier: "A corpse on the first day of Yom Tov, gentiles deal with it. On the second day of Yom Tov, Israelites deal with it. And even on the two days of Yom Tov of Rosh haShana {this distinction is made}, which is not the case as regards an egg." And the Nehardeans say that this distinction is indeed made as regards an egg, and so similarly here, the two days of Rosh haShana have the same status as two days of Yom Tov of the exile -- two separate kedushot -- even as regards an egg, and so too one could make an eruv tavshilin from one day of Yom Tov to the next, as stated above.}

Rav Mordechai said to him: Master {=Rav Ashi} said to me explicitly that he does not hold like this of the Nehardeans.

It was stated {by Amoraim}: A chick that was hatched on Yom Tov:
Rav said: It is forbidden.
And Shmuel, and some say Rabbi Yochanan, said: It is permitted.
Rav said: It is forbidden -- it is muktzeh;
And Shmuel, and some say Rabbi Yochanan, said: It is permitted -- since it permits itself via slaughter.

{See Ran for some resolution. Rif does not resolve here who we rule like. That is, since if it is Shmuel, then we rule like Rav by prohibitions, but if it is Rabbi Yochanan, we rule like Rabbi Yochanan over Rav.}

A calf which was born on Yom Tov is permitted, since it is prepared {muchan} via its mother. And this is where it is established to him that it completed its months {of development in the womb}, but if it is not established to him that it completed it months, it is forbidden until the night of the eighth, and we have already elucidated this matter in Shabbat perek Rabbi Eliezer Omer Im Lo Hevi Keli {Shabbat 136a - see here in the Rif Shabbat 55b}.

{Beitza 7a}
They learnt {in a brayta}: If one slaughters a hen and finds inside it completed eggs, they are permitted to be eaten on Yom Tov. If one slaughters a hen and finds inside it completed eggs, they are permitted to be eaten with milk. And this was where they were not attached to the connective tissue {of the ovaries}, but if they were attached to the connective tissue, it is forbidden to eat them with milk.

Rav Mari son of Rav Kahana said: If one checked a hen's nest on erev Yom Tov and did not find eggs in it, and the next day he arose {early, before daybreak} and found an egg, it is permitted -- for it is known that it must have been laid yesterday {on erev Yom Tov, before nightfall}. For it is established to us that any species which has intercourse {only} during the day gives birth during the day and not at night, and what is this? The hen.

And even though he checked on erev Yom Tov, we say that he did not check very well. And even though he checked very well, we say that the majority of it {the egg} exited and then returned {into the hen} and it is permitted, since it was not {then considered} laid at night, in accordance with Rabbi Yochanan. For Rabbi Yochanan said: An egg which the majority exited on erev Yom Tov, and it returned, it is permitted to eat it on Yom Tov. And this is specifically where there is a male {rooster} with access to it {the hen}, but if there is no male by it, no, for since it becomes heated from {J: excited by rubbing against} the ground, it is possible that it laid at night.