Gemara

R. Chanina ben Dosa had goats. Neighbors complained that the goats were causing losses in their fields. R. Chanina said that if this is so, the goats should be eaten by bears; if not, the goats should bring bears on their horns. (Later, the goats brought bears on their horns.)

Question: R. Chanina was too poor to have goats. Also, it is forbidden to raise small animals in Eretz Yisrael!

Answer (Rav Pinchas): A case occurred, and a man passed by R. Chanina's door and left chickens. R. Chanina's wife found them. He told her not to eat the eggs. They increased greatly and were becoming bothersome, so they sold them for goats.

Bava Kama 79b - Mishnah: We may not raise small animals (i.e. that do not work) in (settled parts of) Eretz Yisrael, but we may raise them in Surya or wildernesses of Eretz Yisrael;

(Gemara - Beraisa #1): We may not raise small animals in Eretz Yisrael, but we may raise them in forests of Eretz Yisrael. In Surya, we may raise them even in settled areas, and all the more so in Chutz la'Aretz;

(Beraisa #2): We may not raise small animals in Eretz Yisrael, but we may raise them in wildernesses of Yehudah or near Ako.

Large animals may be raised, because we do not impose a decree which the majority of the Tzibur cannot fulfill.

It is not necessary to raise small animals. People can get them (for Korbanos or to eat) from Chutz la'Aretz. Large animals are constantly needed for labor. It is not feasible to get them from Chutz la'Aretz.

Even though small animals may not be raised in Eretz Yisrael, one may get one within 30 days of when he needs it for a festival or for his son's wedding feast. He may not keep the last animal 30 days;

One might have thought if one bought some animals 30 days before the Regel and some just before the Regel, he may slaughter the former and keep the latter until 30 days from their purchase. The Beraisa teaches that this is not so. He may not leave them after the Regel at all.

A butcher may buy what he will need to slaughter for the market day. He may not leave the last animal bought after the market day until 30 days (from its purchase).

(Beraisa): Talmidim asked if one may raise small animals; R. Gamliel permitted.

Question: The Mishnah forbids this!

Correction: Rather, they asked if one may keep a small animal for 30 days before the festival. R. Gamliel permitted this, on condition that it does not graze with the herd (e.g. of cattle, which one may raise). Rather, he must tie it to the bed.

(Beraisa): A Chasid was groaning. Doctors said that to be cured he needs warm milk (straight from the animal) every morning. They brought a goat and tied it to his bed. He suckled every morning.

One day his friends came and saw the goat. They were outraged to see an 'armed robber' in his house, and left. They could not find another thing he had done wrong. Just before he died he confessed that his only transgression was disobeying the decree.

R. Yishmael: My father's house in Galil was destroyed because they used to graze small animals in forests and judge monetary cases alone (without a Beis Din of three).

Even though they had forests near their houses, someone else owned a small field on the way to the forest.

(Beraisa): If a shepherd repents, he need not sell his whole flock immediately. He may sell it little by little.

80a - Version #1 (Rav Yehudah citing Rav): In Bavel, we adopted the law of Eretz Yisrael to forbid raising small animals.

Rav Ada bar Ahavah asked Rav Huna why he keeps small animals. Rav Huna said that his wife guards them from damaging. Rav Ada cursed that she should bury her son. As long as Rav Ada was alive, none of Rav Huna's children from her survived.

Version #2 (Rav Huna): After Rav came to Bavel, we adopted the law of Eretz Yisrael to forbid raising small animals.

81a (Beraisa): Yehoshua made the inheritance of Eretz Yisrael conditional on 10 laws: people may graze animals in (others') forests,... people may walk on the side of the road (bordering others' property), to avoid hardened clumps of dirt in the middle;

(Rav Papa): The Heter to graze animals in forests is only for small animals in large forests. There is no Heter for large animals, nor in small forests.

Shmuel and Rav Yehudah were walking on a road (in Bavel); Shmuel went to the side. Rav Yehudah asked if Yehoshua's enactments apply also in Bavel. Shmuel answered 'Yes, they were also for Chutz la'Aretz.'

Rishonim

Rif (Bava Kama 29b): We may not raise small animals in Eretz Yisrael, but we may raise them in Surya or wildernesses of Eretz Yisrael. If a shepherd repents, he need not sell his whole flock immediately. He may sell it little by little. Yehoshua made the inheritance of Eretz Yisrael conditional on 10 laws: people may graze animals in forests...

Nimukei Yosef (DH Masnisin): In Eretz Yisrael we assume that all the fields belong to Yisraelim. Even an animal tied to the bed so that it cannot graze in others' fields is permitted only 30 days before the Regel. "Isru Chag ba'Avosim Ad Karnos ha'Mizbe'ach" hints that the animal must be tied until it is offered. The Heter to graze animals in forests is only for small animals in large forests, so they will not finish off the trees.

Rif (ibid.) and Rosh (Bava Kama 7:18): Rav Ada taught that Yehoshua's laws apply even in Bavel. Shmuel taught that they apply even in Chutz la'Aretz.

Pilpulei Charifta (8): This is unlike our text, but the Halachah is the same.

Rambam (Hilchos Nizkei Mamon 5:1,2): One may not damage and then pay for the damage. Even to cause damage is forbidden. Therefore it is forbidden to raise small Behemos and Chayos in Eretz Yisrael near fields and vineyards. It is permitted in forests and wildernesses, and anywhere in Surya.

Rambam (3): Yehoshua made the inheritance of Eretz Yisrael conditional on 10 laws: people may graze small animals in forests whose trees are big...

Rosh (Bava Kama 7:13): We may not raise small animals in Eretz Yisrael, i.e. even in the house. In the field, even large animals are forbidden. Shepherds are Pasul witnesses because they graze their animals in others' fields. This is only if they graze their own animals, but not if they graze others', for people do not sin to help others. It seems that one may not raise even others' small animals in the house, for even tied to the bed is forbidden. The people of Galil were punished for raising small animals, even though others grazed them. If a shepherd does Teshuvah, (he must eventually sell his entire flock,) we do not allow him to have others graze them for him. We may raise small animals in Surya or in wildernesses of Eretz Yisrael.

Rashba (79b DH v'Ha): It is forbidden even if a shepherd tends them. Even though people do not sin to help others, a broad decree was made. The man who needed milk each morning did not have a solution to give it to a shepherd. This is not a proof, for shepherds normally do not enter the city every morning. Some permit if a shepherd tends them. It seems that Bavel is like Eretz Yisrael for small animals, and in Bavel they used to raise through shepherds. The Gemara said that one may keep an animal only 30 days before the market day or Regel, i.e. it is not the house. There is no limit if it is with a shepherd. It is possible that the Amora'im in Bavel who raised animals did not accept Rav's teaching that Bavel is like Eretz Yisrael. Even Rav Huna, Rav's Talmid, relied on his wife to guard his animals!

Rosh (14): If a shepherd repents, he need not sell his whole flock immediately. He may sell it little by little.

Rosh (16): One of Yehoshua's stipulations for the inheritance of Eretz Yisrael was that people may graze animals in forests. This refers to small animals in forests whose trees are big.

Me'iri (80a DH Af): Even though one may transgress Isurim for Piku'ach Nefesh, one should be more stringent about something forbidden by a decree because it harms others.

Poskim

Shulchan Aruch (CM 409:1): We may not raise small animals in Eretz Yisrael, because they are apt to graze in others' fields; this damage is common. We may raise them in Surya or wildernesses of Eretz Yisrael. Nowadays, it is not common that Yisraelim have fields in Eretz Yisrael, so it seems that (everywhere in Eretz Yisrael) is permitted.

SMA (1): The Tur says that this was forbidden even in the house, even if it is not his animal. Even though a person will not sin to benefit others, small animals are apt to get out and do harm without the shepherd's knowledge.

Tur: Some say that our customs follow Bavel. It seems that this does not apply here. Bavel was like Eretz Yisrael because Yisraelim owned most of the fields. Since this does not apply nowadays, it is permitted.

SMA (2): The law would apply anywhere where Yisraelim are the majority.