Gemara

"Lechayos Zera" excludes Tereifos (from animals in No'ach's ark).

This is like the opinion that a Treifah cannot have children. The opposing opinion learns from "Itach" - the animals should resemble you (Noach).

Chulin 57b (Rav Huna): If an injured animal survives 12 months, this shows that it was not Tereifah.

(Beraisa): A sign of Tereifos is that the animal cannot bear children;

(Rav Acha bar Yakov): The Halachah is, a Tereifah can give birth.

Version #1 - Rav Acha - Ameimar): If a female bird became a Tereifah, eggs that were inside at the time are forbidden. Eggs that formed later are permitted, for Zeh v'Zeh Gorem (if something comes from two sources, and one of them (in this case, the father) is permitted, it) is permitted.

Question (Rav Ashi - Mishnah #1): All agree that eggs of a Tereifah are forbidden, for they grew inside a forbidden bird.

Answer (Ameimar): That refers to eggs that developed without a male (the hen warmed itself in the earth).

Version #2 - Ravina - (Ameimar): If a female bird became a Safek Tereifah, and later it forms more eggs, all the eggs (including what was already inside) are permitted. If it does not form more eggs, the (first) eggs are forbidden.

Mishnah #1 forbids eggs completed inside a forbidden bird.

The Halachah is, a Safek Tereifah male (is Kosher if it lives) 12 months. A female that does not give birth (is forbidden).

Rishonim

Rif (Chulin 19a): If a Safek Tereifah lives 12 months, it is Kosher. If a Safek Tereifah female give birth, it is permitted immediately.

Rosh (3:52): If a Safek Tereifah lives 12 months, it is Kosher. A female that does not give birth (is forbidden).

Ma'adanei Yom Tov (3): Many Kosher animals cease to give birth, yet we do not assume that they are Tereifos! Rather, if an animal gives birth, we know that it is not Tereifah (Tosfos).

Rif and Rosh (ibid.): If a female bird became a Safek Tereifah, we hold onto the eggs that are already inside. If it forms more eggs, (all) the eggs are permitted. If not, they are forbidden.

Rambam (Hilchos Shechitah 11:1): Any animal or bird with one of these Safek Tereifos, e.g. an animal fell and did not walk, or a Drusah, i.e. it was scratched by a (venomous) Chayah and we do not know whether the flesh near the intestines reddened, if it is a male and it lived for 12 months, it is Muchzak to be intact, like all other animals. If it is a female, (it is a Safek) until it gives birth. A male bird (is a Safek) until 12 months, and a female until it lays all the eggs it was carrying, and bears more eggs and lays them.

Rashba (Teshuvah 1:98): If an animal has an extra limb, it is considered as if it is missing that limb, so if loss of that limb would make the animal Tereifah, it is Tereifah. Even if it lived 12 months, do not heed one who is Machshir it, or any other Tereifah. He slanders Divrei Chachamim. Living 12 months or giving birth helps only for Safek Tereifos. Watever Chachamim called a Vadai Tereifah can never be permitted. The Gemara asked about cases in which Tereifos were cured and lived, and it answered that they did not live 12 months. Even if many will say that it lived longer, we contradict them, to preserve Divrei Chachamim. Do not say that Chachamim merely discussed the majority, but perhaps a minority can live. This contradicts the Mishnah which says 'any (injury) in which nothing with the same injury lives, it is Tereifah.' If one lives, this proves that the injury is not a Tereifah, or it was a miracle.

Shach (YD 57:48): The Rashba holds that if it lived 12 months, it was a miracle, but it is Tereifah. However, the Maharshal says that a tiny minority can live more than 12 months. If Poskim argue about whether or not something is a Tereifah, if it lives 12 months, it is Kosher. This is correct. The Rashba holds that living 12 months does not Machshir any Vadai Tereifah. The Levush says so only about an extra limb. This is wrong.

Pri Megadim: If a slaughtered animal was found to have two livers, if it was at least 12 months old it is Kosher, for surely the extra liver was there from birth. The fact that it lived 12 months would resolve the argument of Rashi and the Ramban about this, like the Maharshal said. However, if most Poskim say that it is Tereifah, I am unsure if we rely on 12 months to resolve that it is Kosher. Perhaps the Torah says that we follow such a majority, especially if the Poskim saw each other. If an animal swallowed a needle, and later it emerged from the animal's back, and it lived 12 months, do we say that this is from the tiny minority of Tereifos that live more than 12 months? Or, perhaps the needle did not go through the Veshet (foodpipe), unlike the majority of what is swallowed. I do not know the law.

Poskim

Shulchan Aruch (YD 57:18): Some say that whenever Chachamim mentioned checking an animal, e.g. it was Drusah, fell or broke (its ribs or the spine), nowadays we are not proficient to check, so the only way to permit is to leave it for 12 months, or if a female becomes pregnant and gives birth.

Shach (42): Delaying 12 months or giving birth helps even if it Vadai was Drusah, since there is a test (to see if a Drusah is Kosher). The Rema says that living 12 months does not help for a truly Vadai Tereifah.

Shach (43): In a leap year, 13 months are required.

Shach (44): Surely, 12 months help also for a female.

Shach (45): The Maharshal says that it must give birth. Pregnancy is not enough. Perhaps it became pregnant but will not give birth!

Pischei Teshuvah (17): The Shulchan Aruch connotes that even if we know that a male fathered a child, it Churban Tereifah. See Mayim Chayim (from the Pri Chodosh, Siman 2) Orach Mishor and Be'er Yakov.

Note: They say that a Tereifah cannot father. Mayim Chayim brings a marginal note that Tosfos Shantz was unsure about this.

Shulchan Aruch (ibid): Similarly, if a bird laid all the eggs it was carrying, delayed 21 days and laid more eggs, it is Kosher. Similarly, if it never laid eggs, and 21 days after it became Safek Tereifah it began to lay eggs, it is Kosher.

Beis Yosef (DH v'Chasuv, citing Orchos Chayim): Laying a new brood permits when it delayed 21 days in between, for this is the gestation (term of pregnancy - Bechoros 8a). If it laid more eggs within 21 days, we say that they are from the first brood, and all are forbidden.

Rema: Some are stringent to forbid leaving a Safek Tereifah for 12 months, lest Takalah result (one will eat it beforehand).

Shach (47 and Taz 86:16): When we must live a bird for 21 days, we are not concerned for Takalah in such a short time.

Rema: Any Vadai Tereifah, even if it lived 12 months, is forbidden.

Pischei Teshuvah (24): Be'er Heitev of the Maharit (37) says that 12 months helps for Drusah and an animal that fell, but not if a bird's wing was broken, for we are concerned lest the lung was punctured in the last 12 months. Even if it gave birth we are concerned lest the lung was punctured after it became full of eggs, so the eggs are forbidden. However, if the wing came off it is Kosher, for we are concerned for a puncture in the lungs only at the time the wing comes off. Many erred about this. Bnei Chiya says that likewise, 12 months does not help for a broken bone where this makes it a Tereifah, lest the bone left (the skin). However, if it was tied, we rely on 12 months or birth; we are not concerned lest it was not tied well and left.

Shulchan Aruch (86:9): A Tereifah does not give birth. Therefore, if a bird was Safek Tereifah and it laid eggs, we wait until it lays all the eggs it was carrying, and if it bears more eggs, it is Kosher. We know this if it delayed 21 days between the end of the first brood and the start of the second, for this is the gestation. Similarly, if a hen never laid eggs, and it became Safek Tereifah, if it laid eggs 21 days later, it and the eggs are Kosher.

Beis Yosef (DH Tereifah): It seems that the Halachah follows Version #2 in the Gemara. All Poskim rule like it.