“And the angel of Hashem said to him, ‘why did you strike your ass these three times?’”
“And the angel of Hashem said to him, ‘why did you strike your ass these three times?’”
Animal experimentation is an integral part of scientific research in a variety of fields, particularly the field of medicine. Scientists routinely use animals for research into the pathophysiology of disease, drug development, and general biology and genetics.
In recent decades, this method of research and development has been the focus of enormous controversy in the Western world. Although the majority of people do not dispute the critical importance of these experiments in developing life-saving medications and procedures, there are those who oppose any use of animals for human benefit. As a result, many countries have legislated restrictions on animal experimentation to ensure that research is carried out only for medical purposes and not for other uses (e.g. cosmetics and other consumer products).
In the following paragraphs we will outline some of the opinions of the Poskim regarding Tza’ar Ba’alei Chaim: Is it permitted to cause animals pain for the benefit of humans? Is there any distinction based on the degree of pain or the purpose of the experimentation?
The Tanaim and Amoraim (Bava Metzia 32b-33a) (and thereafter, the Rishonim and Poskim) dispute whether the prohibition of Tza’ar Ba’alei Chaim is an Issur d’Oraisa or d’Rabanan.
Among those who hold that it is an Issur d’Oraisa there are various opinions as to its source in the Torah. Some hold that it is derived from the Mitzva to help unload a donkey that is struggling with its load (see Shemos 23:5). Others maintain that it is learnt from the prohibition to muzzle an ox while it is threshing which prevents it from eating while it works.
A third opinion is that it is implicit in the Posuk in Tehilim (145:9) which states “and His mercy is upon all His creations”. Since Hashem has mercy on everything He created, including the animals, and man is enjoined to emulate His Middos, he must also have mercy on the animals and prevent them from suffering.
The Rambam (Moreh Nevuchim 3:17) fascinatingly derives the prohibition of Tza’ar Ba’alei Chaim from the Posuk in our Parsha when the Malach rebukes Bilam for hitting his donkey. This teaches us that it had been an incorrect thing to do!
Tza’ar Ba’alei Chaim is considered to be a grave sin and warrants a severe punishment. The Gemara (Bava Metzia 85a) relates that Rebbi Yehuda ha’Nasi suffered severely for many years because on one occasion he had not acted mercifully to a calf that was on its way to be slaughtered. The calf ran in fright and buried its head in Rebbi’s clothes and cried, but Rebbi said to it sternly “go, this is what you were created for”. In Heaven at that time it was decreed that Rebbi would suffer because he did not act mercifully.
The Gemara also relates that Rebbi’s suffering eventually came to an end when he did act mercifully to animals. He once saw his maidservant sweeping out some baby weasels that had taken up residence in his house but he stopped her. “The Torah says that G-d’s mercy is upon all of his creations”, he told her. At that time in Heaven it was decreed, “since he was merciful, we will be merciful to him”.
The importance of Tza’ar Ba’alei Chaim notwithstanding, all of the Poskim agree that Man was created to be the pinnacle of creation. Hashem placed Man in charge of the natural world, including the animal kingdom, and, therefore, everything may be used for his benefit. For this reason, the Torah permitted the slaughter of animals for food and to make use of their hides. The Rishonim and Acharonim discuss whether the prohibition of Tza’ar Ba’alei Chaim applies only when there is no human benefit or even when there is some human benefit and what the parameters and criteria are for permitting it.
The earliest known source is the Teshuvos ha’Geonim (375) which states clearly that Tza’ar Ba’alei Chaim is only forbidden when there is no purpose (e.g. “for Mazel or Refua”). The Ran in Maseches Shabbos (154b) concurs. He argues that Tza’ar Ba’alei Chaim must be permitted when it benefits humans else it should be forbidden to have one’s donkey grind wheat because of the discomfort of the donkey! The Rema (E.H. 5) rules similarly in the name of the Issur v’Heter he’Aruch (59).
The Rema (ibid.) further cites a ruling of the Terumas haDeshen (105) permitting plucking feathers from live ducks. However, as Terumas haDeshen himself notes, “the people refrain from doing so because it is cruel”.
Interestingly, the Terumas haDeshen was not discussing a case where there was a need for duck feathers for Refua or some other legitimate purpose. Rather, he ruled leniently even when there was no apparent purpose since the world was created for man’s usage. Nevertheless, as he notes, people refrain from such activities because of cruelty.
The Shoel u’Meishiv (Yosef Da’as Y.D. 348) offers a novel explanation as to why Tza’ar Ba’alei Chaim is permitted when it serves the purpose of humans. He explains that the reason for the prohibition of Tza’ar Ba’alei Chaim is to engender a trait of Rachmanus (mercy) in the Jewish people and not simply because Hashem is merciful to all living creatures. It follows that any act that causes pain to an animal should be permitted as long as it was not intended as cruelty.
The Shoel u’Meishiv’s explanation can be supported by the words of the Sefer ha’Chinuch (Mitzva 596) regarding the prohibition of muzzling one’s ox during threshing. The Chinuch does not attribute this prohibition merely to the ideal of saving an animal from needless pain, but also “to teach us to be people with good hearts, who choose to do what is just and to cleave to it, and to pursue kindness and compassion. And when we accustom ourselves to acting as such even with animals who were only created to serve us… the soul will become accustomed to it and will endeavor to do good with people as well…” We see that the purpose of the prohibition is to accustom people to compassion and kindness.
This perspective is quite unlike that of the modern animal rights activists who reject any hierarchy of man over the animals and believe that the two should be held as equals and that man should have no right to cause any harm to animals. Our belief, by contrast, is that the hierarchy of man over the animal kingdom is a part of creation, but we nevertheless have an obligation to avoid causing animals any needless pain so that we learn to be compassionate.
Many later Poskim invoked the ruling of the Terumas haDeshen to forbid Tza’ar Ba’alei Chaim on moral grounds when it serves no useful purpose. Noda biYehuda (Mahdura Tinyana Y.D. 6) famously decried the custom of the rich who would go fox-hunting as a pastime. “How can a Jewish person kill a living creature with his own hands just to pass the time?” he wrote. “It is only permitted for the purposes of making a livelihood.”
Let us now examine the rulings of the Poskim regarding using animals for medical experimentation. As stated above, the Rema (in the name of the Issur v’Hetter) permits Tza’ar Ba’alei Chaim for the purposes of Refua, even for the sake of a person who is not in danger of dying. At the same time, it is important to avoid cruelty as much as possible.
The Shevus Ya’akov (Y.D. 3:71) was asked by a Jewish doctor whether it was permitted for him to perform medical experiments on animals. The doctor claimed that since his experiments would not kill the animals but would merely cause a perforation of their internal organs, the ruling ought to be more lenient. The Shevus Ya’akov pointed out to him that, on the contrary, it would be better if the experiments would kill the animals painlessly, rather than leaving then alive to suffer the consequences of the experimentation.
Nevertheless, the Shevus Ya’akov ruled that it was permitted for the doctor to experiment on the animals even if it wasn’t certain that doing so would lead to a Refua for human beings. He also wrote that the custom cited by the Rema to avoid plucking feathers from ducks because of cruelty, was only because plucking the feathers was a direct act that caused pain to the animal. Administering an experimental medication to an animal that does not directly cause pain to the animal, although it may cause pain or suffering at some future time, is not considered an act of cruelty.
It follows that according to the Shevus Ya’akov, if experimenting on an animal will cause it immediate pain, it would be Midas Chasidus (pious conduct) to refrain from it even if it is done for the purpose of Refua. The Chelkas Ya’akov (1:30) concurs.
However, the Seridei Aish (3:7) disagreed. He argued that Midas Chasidus can only be invoked when dealing exclusively with an individual person who is being advised to act or behave piously. In our case, where the outcome of this experimentation will (hopefully) benefit the general public, there is no room to acting “piously” at the expense of others. Therefore, all experiments on animals for the purposes of Refua would be permitted.
The Tzitz Eliezer (14:68) discusses the question of surgically removing the eyes of hares in order to try and develop a cure for diseases of the eyes. He rules conclusively that it is permitted (and that it is not even “Midas Chasidus” to refrain from it) for if it is permitted to make use of animals for non-essential purposes, it should certainly be permitted for Refua. However, it is preferable to make the process painless for the animals, such as by using local anesthetic and performing the surgery quickly.
It is clear from the above, that the basis of the prohibition of Tza’ar Ba’alei Chaim is a moral duty to refrain from acts of cruelty and to be merciful towards all of Hashem’s creations. Therefore, despite the clear conclusion of the Poskim permitting experimenting on animals for the purposes of Refua, it is still important to limit the animals’ suffering as much as possible. In all cases, one should find a substitute whenever possible (e.g. using simulations instead of animals for medical education), and one should always take care to ensure that the animals are well-fed and cared for, and to use anesthesia and provide analgesia whenever possible during the experiments.
In many cases, the animals used for medical experiments are rodents (rats and mice). One might assume that the prohibition of Tza’ar Ba’alei Chaim would apply to these animals no less than any other and that is in fact clearly stated by the Kitzur Shulchan Aruch (191:1).
However, Rav Yaakov Emden zt”l (Sheilas Ya’avetz 1:17) writes that Tza’ar Ba’alei Chaim only applies to animals that are domesticated or those that can be trained, but not fleas, for example. Though Rebbi was rewarded for not allowing his maidservant to evict weasels (which are not domesticated) from his home, that was because he was a “Kadosh and a Chassid” and Hashem expected him to show mercy to all creatures.
Rav Moshe Feinstein zt”l (Igros Moshe C.M. 2:47) has an alternate approach and rules that Tza’ar Ba’alei Chaim does not apply to animals that cause discomfort to a person (e.g. flies, fleas, or mice). The weasels that took up residence in Rebbi’s home were a species that do not cause any harm to people at all. He was therefore expected to be merciful towards them.
Therefore, it is
possible that according to the Ya’avetz it would be permitted to
experiment on any non-domesticated animals, but according to Rav Moshe zt”l
it would only be permitted to experiment on those that are harmful or annoying
 Obviously, we cannot tackle this entire topic in this forum. We will cite a selection of the material on the topic and attempt to present the main sources that are the basis for practical Halacha.
 See Rashi to Shabbos 128b, Meiri to Bava Metzia 32b, Shu”t Radva”z 1542, Ritv”a to Bava Metzia ibid., Sefer Chareidim Chap. 14 et. al.
 Bamidbar 22:32
 He also permitted trimming a dog’s ears in order to beautify it.
 However, see the Shevus Ya’akov cited later regarding this Terumas haDeshen.
 It should be noted that those Rishonim who derived the prohibition of Tza’ar Ba’alei Chaim from the Posuk that stated that Hashem is “merciful to all of his creations” would seemingly agree that the essence of the prohibition is to avoid causing pain to animals and not necessarily to instill elevated morals in man.
 For more on this topic see Shevus Ya’akov (Y.D. 3:71), Chelkas Ya’akov (1:30), Seridei Aish (3:7) and Tzitz Eliezer (14:68).
 The ruling of the Shevus Ya’akov is also cited by the Beis Ephraim (Y.D. 116)
 There is a discussion among the Poskim regarding Tza’ar Ba’alei Chaim of flies, fish, and the like, which is beyond the scope of this essay.
 Such as a dog which can guard people or possessions.