Gemara

Chelev of a Treifah and Chelev of a Neveilah may be used for any use, but you may not eat it" teaches that the Lavim of Neveilah and Treifah take effect in addition to the Lav of Chelev.

117a - Question (Rav Mari): If a sheep's tail is called Chelev, it should be forbidden to eat (even in a Chulin animal)!

Answer (Rav Zvid): The Torah forbids "All Chelev of an ox, sheep or goat," only Chelev that is common to all three animals.

Zevachim 70a: "Chelev Neveilah" refers to animals whose Chelev is forbidden due to Chelev, and not due to eating a Tamei species!

Pesachim 23a - Question: Regarding Sheratzim it says "Sheketz Hu Lo Ye'achel," yet one may benefit from them!

(Mishnah): If hunters of Chayos, birds and fish happened to catch Tamei species, they may sell them to Nochrim.

Answer: There is different, for it says "Lachem". They are yours (to benefit from them).

Question: If so, it should be permitted to hunt them l'Chatchilah!

Answer: It says "Yihyu" - they retain their initial status.

Bava Kama 82b (Beraisa): Aristobulus (a Chashmonai king) was besieging Yerushalayim. Every day, those inside lowered a basket of coins over the wall, and the besiegers gave lambs for the Tamid, which were lifted over the wall. One day, they gave a pig. When the pig was halfway up, it stuck its claws into the wall. All of Eretz Yisrael shook 400 Parsah by 400 Parsah.

Chachamim imposed a curse on anyone who will raise pigs.

Shevi'is 7:3 (Mishnah): One may not do business with Neveilos, Treifos, Sheratzim u'Rmasim.

7:4 (Mishnah): If a hunter of Chayos, birds or fish happened to catch Tamei species, he may sell them.

Rishonim

Rambam (Hilchos Ma'achalos Asuros 8:16): Any thing that one may not eat but one may benefit from it, one may not do business with it or intend to do his Melachah with it, except for Chelev, for it says "it may be used for any Melachah."

Rosh (Bava Kama 7:13): A Yisrael may not raise pigs anywhere, i.e. even to anoint hides. The Torah forbids selling them to Nochrim is forbidden mid'Oraisa, like we expounded in Pesachim.

Tosfos (Bava Kama 82b DH Lo): Why does the Mishnah forbid raising pigs? One may not raise any Tamei animal, like it says in Shevi'is! R. Tam answered that this is only regarding matters destined to be eaten. If one raises them to grease hides with their fat, or to sell to Yisre'elim for this, it is permitted. One may sell any Chelev if it is not destined to be eaten. The Yerushalmi permits doing business with donkeys and camels because they are for Melachah.

Tosfos (Pesachim 23a DH Amar): We can say that Bava Kama taught a curse for one who will raise pigs. Alternatively, the Torah forbids only selling to Nochrim to eat. One may profit with the fat or skins of Tamei species; this was forbidden regarding pigs. Alternatively, even if one chanced upon them, e.g. he inherited them, one may not raise pigs.

Rashba (3:223): The Torah permits eating Tamei species. It says "Lachem Yihyu." In Pesachim, we expounded from this that one may benefit from them. Therefore, I permitted collecting a loan from pigs, for this is saving from them (the Nochri borrowers).

Terumas ha'Deshen (200): May one lend to Nochrim on Ribis if he gives sides of pigs for collateral? The Torah forbids business with Tamei species; we expound it from a verse (Pesachim 23a). R. Shimshon (Shevi'is 7:3) says that Chachamim permitted only professional hunters. The Yerushalmi explains that this is because the government collects taxes. Even according to this, we can permit lending on Ribis using Temei'im for security, for the government collects taxes primarily due to loans with Ribis. In any case it is repulsive for Yisre'elim to lend on security of swine. From Maharam it seems that one may buy and sell Chelev l'Chatchilah, even if it is destined to be eaten. Tosfos forbids in this case; I wrote what seems to me.

Tosfos (Yoma 77a DH d'Tanan): One may anoint with Chelev. Anointing is like drinking only regarding Yom Kipur, Terumah and Isurei Hana'ah. One who puts raw Chelev of a Shor ha'Niskal (an ox sentenced to be stoned) on his wound is exempt. If it were cooked, it would be forbidden. This is because it is Asur b'Hana'ah. Chelev that one may benefit from, one may anoint with it.

Poskim

Shulchan Aruch (YD 117:1): Anything that the Torah forbids, even if one may benefit from it, if it is special for food, one may not do business with it (Rema - or accept it for collateral), even to buy it to feed to one's Nochri workers. The only exception is Chelev, for the Torah said "it may be used for any Melachah."

Beis Yosef (DH Kasuv): Orchos Chayim says that some permit business with Chelev of pigs. The Torah did not distinguish between Tahor and Tamei Chelev. I disagree. The Torah permitted Chelev of a Tereifah or Neveilah. Tereifah and Neveilah do not apply to pigs!

Bach (DH Kasav): Another proof that the Torah permits business with Chelev only of Tahor animals is that only Chelev of cattle, goats and sheep is called Chelev, like it says in Chulin (117a, 75a). The Beis Yosef brings this (Reish Siman 64), and it is explicit in the Rambam (Hilchos Ma'achalos Asuros 2:2, 7:1). Surely one may anoint with it, even for Choleh (sick person) without danger.

Note: The Gemara and Beis Yosef say that only Chelev of the three Tahor animals is forbidden. The Rambam says that regarding all other animals, the Chelev is like the meat.

Shach (4): We permit only Chelev of Tahor animals. The Beis Yosef connotes that one may not do business with Chelev of Tamei animals. In the Shulchan Aruch he did not specify. He relied on the verse he brought. Stam Chelev is of a Tahor animal. This is unlike Orchos Chayim, who says that the Torah did not distinguish between Chelev or Tahor and Tamei animals. This is unlike Zevachim 70a, which says that the verse discusses only Tahor animals. This Isur (to sell Chelev of Tamei animals) is only for the sake of eating. If it is for greasing hides, one may sell it.

Taz (4): The Beis Yosef brought from Orchos Chayim that one may not anoint himself with Chelev of pigs, for anoinintg is included in drinking. I say that the Halachah does not follow this. Tosfos permits anointing with Chelev that one may benefit from. In Siman 123, The Beis Yosef brings that the Rashba permits anointing with pig Chelev even if there is no danger. Isur v'Heter (Sof 39) permits anointing with Chelev or pig (lard) only if one is in pain. A healthy person may not do so for pleasure. Therefore, one should not anoint a young child with pig Chelev, since it is only for pleasure. One may tell a Nochri to do so. Adults are forbidden to do so only themselves (but they may tell others to do so). This is correct. The Levush forbids pig Chelev, but permits other Chelev. There is no source to distinguish.

Rema: One may collect a loan from Nochrim from Tamei species, for this is like saving from them.

Shulchan Aruch (CM 409:2): One may not raise pigs anywhere, even to anoint hides, and all the more so one may not raise them for business.

Bach (YD 117 DH Zeh): The Rosh forbids raising pigs even to anoint hides. R. Tam and the Agudah permit. This is wrong. The Tur forbids raising them Stam. He did not give any Heterim. The Beis Yosef rules like this. The Rashba was astounded at Tosfos.

Shach (117:1): R. Tam permits raising Tamei species to grease hides with their fat, or to sell to Yisre'elim for this, or to use their fat for burning. Everything is forbidden regarding pigs, due to the episode that occurred. The Tur and Shulchan Aruch (CM 409) say so, and also the Rosh, Agudah, Nimukei Yosef and Ro'oh. The Bach says that the Rosh argues with R. Tam and the Agudah. This is wrong.

Bach (ibid.): Nowadays, some Yisre'elim rent from the mayor all his income, including pigs in the Chatzer. The Yisrael raises them. There is no Heter for this. They should be excommunicated. They never saw a Siman Berachah from this. One who collects a debt from the mayor should be careful not to take pigs, or at least to sell them immediately, unless this will anger the mayor. Even though the Rashba permitted to take pigs, for this is like saving from them, Orchos Chayim says that a hunter who caught Tamei species must sell them immediately. He may not wait for them to fatten. All the more so one may not keep them to feed to Nochri workers.

Taz (117:4): Perhaps we can permit, for the Yisrael intends primarily for permitted matters of the mayor. The Tamei things are secondary. The Tur connotes that a hunter may intend for Tamei species alomg with Tehorim. This is because one cannot hunt just Tehorim without catching also Temei'im.

Shach (11): One who collected Tamei species for a debt must sell them immediately. He may keep them until he can sell them for the debt, even if they are pigs (Teshuvas Menachem Azaryah 30, Masas Binyamin 36), but not to profit more than the debt he was owed.

Shach (12): The Rashba permits collecting even pigs for a debt.