The Torah commands in Parashat Ki-Teseh (Debarim 22:10), “Lo Taharosh Be’shor U’ba’hamor Yahdav,” forbidding plowing a field with an ox and donkey together at the same time. The Sefer Ha’hinuch explains, based on the Rambam’s understanding of this law, that the Torah here prohibits having an animal from a kosher species and an animal from a non-kosher species perform any kind of work together.
The Rambam, as cited by the Sefer Ha’hinuch, viewed this prohibition as related to the separate prohibition which forbids crossbreeding different species of animals. Farmers who would use two different species of animals for plowing fields would then bring them into the barn and mate them. Plowing with different species of animal is thus associated with crossbreeding, and so the Torah forbade plowing with different species as part of its prohibition against crossbreeding different species.
The Meshech Hochma (Rav Meir Simha Ha’kohen of Dvinsk, Lithuania, 1843-1926) questions the Rambam’s explanation, noting that when a kosher species of animal is crossbred with a non-kosher species, this does not result in conception. Kosher species and non-kosher species are incapable of reproducing together, and thus it seems difficult to understand why the Torah would need to forbid plowing with kosher and non-kosher species of animal as a safeguard against crossbreeding.
The Sefer Ha’hinuch adds a different reason, explaining that it causes an animal distress to have to work together with an animal from a different species. Animals feel more comfortable and at ease with members of their own species, and thus in the interest of avoiding Sa’ar Ba’aleh Haim (distress to animals), the Torah forbids forcing two different species to work together. The Sefer Ha’hinuch adds that we learn from this command a practical lesson for everyday life – that we should not appoint two people for a job or position if they are not compatible. If the Torah forbids forcing two animals to work together if this would cause them hardship, then certainly, we should be sensitive when pairing people together, and ensure not to assign a job to people who do not get along well with one another.
This prohibition applies to both Behemot (domesticated animals) and Hayot (non-domesticated animals). As mentioned, according to the Sefer Ha’hinuch, the Torah prohibition forbids having work done by a kosher species of animal together with a forbidden species of animal. Having two different kosher species, or two different non-kosher species, work together is forbidden by force of Rabbinic enactment. It is permissible to have a person and an animal work together, because a human being is fundamentally distinct from an animal, and thus the animal does not sense any connection to the person such that he would experience discomfort working with him.
This command is binding upon both men and women, and applies in all times and all places. One who makes an animal from a kosher species work together with an animal from a non-kosher species is liable to Malkut, even if he has them work by making noise, such as by shouting. Although speech generally is not considered a “Ma’aseh” (“action”) that suffices for liability to Malkut, this prohibition marks an exception to the rule, and having the animals work even verbally, without performing an action, renders one liable to Malkut for transgressing this Biblical command. If one has animals from two different kosher species, or from two different non-kosher species, work together, then he receives Malkut for transgressing the Rabbis’ enactment.