Medical Experiments Performed on Animals
According to Halakha, inflicting unnecessary pain on animals (tza'ar ba'alei chayyim) is forbidden by Torah law. Various halakhot follow from this general principle. For example, if a person comes across two people on the road, one loading his animal and another unloading his animal, both of whom he is required by Torah law to assist, he must first help the one unloading his animal, so as to relieve the animal of its burden (Rambam, Hilkhot Rotze'ach 13:13).
The prohibition of tza'ar ba'alei chayyim does not apply, however, when the mistreatment is necessary for some human benefit. Thus rules the Rema, in line with the Terumat ha-Deshen:
The prohibition against inflicting pain on animals does not apply to anything necessary for a medicinal purpose or other uses. One is, therefore, permitted to pluck the feathers of a live goose, without being concerned about tza'ar ba'alei chayyim. Nevertheless, people refrain [from such a practice] because it involves cruelty. (Rema, Shulchan Arukh, Even ha-Ezer 5:14)
Some authorities adduce support for this principle from the Gemara in Shabbat which permits a person to castrate a rooster for some beneficial purpose in a manner that causes the rooster to suffer:
For Rabbi Yochanan said: If one wishes to castrate a rooster, let him cut off its crest, and it is automatically castrated. (Shabbat 110b)
A fascinating responsum of the Noda Biyehuda deals with the permissibility of sport hunting:
The root of his question: Regarding a certain person to whom God granted an expansive estate, containing villages and forests that are swarming with animals – is he himself permitted to go hunting with a gun, or is a Jew forbidden to do such a thing, whether because of the prohibition to inflict pain upon animals or because of the prohibition to destroy things of value…
It is, however, unnecessary to discuss this at length, for the Terumat ha-Deshen (Pesakim u-Khetavim, no. 105) has already written that anything done for some human need does not constitute tza'ar ba'alei chayyim. Moreover, this prohibition only applies when a person tortures a live animal. But killing cattle, beasts, or any other animals does not fall into the category of tza'ar ba'alei chayyim… Thus the case in question does not involve tza'ar ba'alei chayyim. As for the prohibition to destroy things of value, this certainly does not apply, for he benefits from the hide. And he does not act with destructive intent… These animals of the forest, while they are alive, do not benefit man in any way. The primary benefit [that they provide] is when they are dead, by way of their hides and flesh. How then can we say that one is forbidden to kill them because of the prohibition to destroy things of value…
Thus far we have spoken on the level of strict law. I am, however, amazed by the thing itself. The only hunters that we find are Nimrod and Esav. This is not the way of the descendants of Avraham, Yitzchak and Ya'akov… How can a Jew kill a living creature with his own hands for no purpose, just to pass the time engaged in hunting… to chase [animals] in the forests, the place where they live, when they are not wont to enter populated areas. There is no mitzva here, only chasing after the lusts of the heart. Someone who needs to do this, and whose livelihood comes from such hunting – this does not involve cruelty… But for someone who is not required to do this for his livelihood, and whose main intention is not for his livelihood, this is cruelty. (Responsa Noda Biyehuda, mahadura tinyana, Yore De'a, no. 10)
The Noda Biyehuda vigorously rejects hunting as a sport. This is not for reasons of strict Halakha, but because the pastime involves cruelty to animals. For our purposes, the Noda Biyehuda confirms the Rema's ruling, that anything done for some human benefit does not constitute cruelty. He adds another important criterion: Torturing an animal and causing it pain fall into the prohibition of tza'ar ba'alei chayyim, but killing an animal does not. It should be noted that the author of Responsa Chelkat Ya'akov expressed astonishment regarding the Noda Biyehuda's ruling, for hunters often succeed only to wound their prey, but not to kill them, and this certainly involves tza'ar ba'alei chayyim.
The author of Responsa Shevut Ya'akov (eighteenth century) is lenient about medical experiments:
I was asked by an expert doctor, R. David Wiesel, whether it is permissible to prepare a potion that may involve the killing of an unclean animal, such as a dog or a cat, on the grounds of uncertain piku'ach nefesh. For the potion had not yet been tried or tested, and it can be tested by giving it to a dog or a cat to drink, and seeing whether it dies…
Answer: …They ruled in practice that anything done for some need, either to heal the body or for some monetary benefit, does not constitute forbidden destruction of things of value or tza'ar ba'alei chayyim. There is not even a code for the pious here… one may do this even lekhatchila. Even though the Rema concludes there in Even ha-Ezer (end of sec. 5) regarding the plucking of feathers, that people refrain [from such a practice] because it involves cruelty – that is only in the case of plucking feathers, where he acts with his hands, and the bird feels great pain with each and every plucking. This is not true in the case before us, where the animal experiences no pain while eating or drinking [the potion]. Only afterwards does it cause it illness and pain, and this is for the sake of healing a person. It seems obvious to me that there is no concern of prohibition whatsoever, even as an act of piety. (Responsa Shevut Ya'akov, III, no. 71)
The Shevut Ya'akov proposes a formal distinction: The prohibition based on cruelty, which is merely a pious supererogation, only applies when one inflicts pain directly. This, however, is a very formal distinction, and it is strange to find such a distinction with respect to acts of piety.
The author of Responsa Chelkat Ya'akov (
What follows from all this is that according to [the standards of] strict law, one is certainly permitted to inflict pain upon animals in the course of experiments conducted for the sake of scientific research and medical knowledge. But according to [the standards of] piety, to save oneself from the trait of cruelty, this is certainly forbidden, following the ruling of the Rema (Even ha-Ezer, end of sec. 5) regarding the plucking of feathers from live birds. Only in the case of ritual slaughter is it permitted, as in sec. 24 of Yore De'a, because it is impossible any other way, but for some [other] need, it is forbidden because of cruelty…
I received the book, Otzar ha-Posekim, and I saw that it brings (at the end of sec. 5) in the name of the Imrei Shefer of the Gaon, R. A. Klutzkin, that the Rema means to issue an allowance only in a place of necessity, similar to medicine, which is a necessary matter, but not for some financial benefit… In my humble opinion, what he says is incorrect, for the talmudic passage in Shabbat 110, "If one wishes to castrate a rooster, let him cut off its crest," implies that this is permitted even for some financial benefit. (Responsa Chelkat Ya'akov, Choshen Mishpat, no. 34)
The Chelkat Ya'akov argues that by strict law, whatever is done for any need whatsoever, does not fall into the category of tza'ar ba'alei chayyim. Thus, he rejects the position of the Imrei Shefer who permits the infliction of pain upon animals only for some great need, such as for medical treatment. The ethical prohibition based on cruelty, however, applies wherever some alternative exists, even with respect to scientific research and medical experiments. This distinction requires careful examination. Why is ritual slaughter regarded as offering no alternative, while medical experiments are treated differently? Surely we can pass on eating meat, this often being much less necessary than certain medical experiments!
The author of the Seridei Esh responds to the author of the Chelkat Ya'akov, and sweepingly permits medical experiments conducted on animals:
One is permitted to inflict pain upon animals for the benefit of medical knowledge. What is more, in my opinion, there is no element of pious conduct here, for pious conduct applies to something that relates solely to the person himself, regarding which a person may be stringent, but not to something that relates to others. For why do you give greater weight to the pain of animals than to the pain of the sick, who perhaps could be helped? (Responsa Seridei Esh, II, no. 91)
It should be noted that all that was said above is applicable to medical experiments. Further study is required regarding testing cosmetic products, and the like.
 The reference is according to the new edition of these responsa, which is included in Bar Ilan's responsa project.
(Translated by David Strauss)