Chullin 80

On yesterday’s daf we encountered the following beraita:

The sages taught: The prohibition against slaughtering an animal and its offspring applies to the offspring of diverse kinds of animals and to the koy.

As we now know, the Torah forbids slaughtering a mother of a domesticated species and her young on the same day. This beraita establishes the principle that this applies also to the offspring of “diverse kinds,” meaning mixed species — such as, for instance, a mule, which is the offspring of a horse and a donkey. And thanks to this beraita, we know it also applies to an animal called a koy. Whatever that is.

We met the koy back on Nazir 34. What was clear then is that the rabbis think of it as an animal that doesn’t fit neatly into categories. Is it domesticated? Is it wild? Is it both? Or perhaps neither? The beraita from yesterday’s daf continues:

Rabbi Eliezer says: With regard to a hybrid that results from the mating of a goat and a ewe, the prohibition of a mother and its offspring applies; with regard to a koy, the prohibition of a mother and its offspring does not apply.
 
Rav Hisda says: What is the koy about which Rabbi Eliezer and the rabbis disagree? It is that which results from the mating of a goat and a doe.

Now we finally have an answer about what a koy is! It is the product of a goat (a domesticated animal) and a doe (a wild animal). That is, we “know” what it is until today’s daf, when that answer is again thrown into question:

Rav Yehuda says: A koy is a single species, and the sages simply did not determine whether it is a species of domesticated animal or a species of undomesticated animal. 
Rav Naĥman says: The koy is the wild ram.
 
So perhaps the koy is not the offspring of a goat and a doe after all. Perhaps it is simply a species the sages are unable to identify as either domesticated or undomesticated.

This dispute is echoed by a beraita, which then adds:

Rabban Shimon ben Gamliel says: It is a species of domesticated animal, and the members of the house of Dushai would raise flocks and flocks of them, as with other domesticated animals.

Rabban Shimon ben Gamliel’s attestation that he heard of a case where someone raised koy in large flocks aside, this all brings us back where we started: We really have no idea what a koy is.
 
For us moderns, there is an additional layer of mystery. The Talmud mentions a wide variety of species (and sub-species) of animals. Identifying exactly what species it is referring to can be complicated as the Talmud names the animals, but does not provide images or, much of the time, a description of distinguishing physical characteristics. Sometimes if the term appears in Modern Hebrew, that can help us identify the animal. Other times, a linguistic connection can be deceiving, as those who were involved in the revival of spoken Hebrew often imported biblical and rabbinic animal names and assigned them to similar but not identical species.
 
On today’s daf, we see that the rabbis of the Talmud had similar challenges. It is unclear to them if a koy is a distinct species or the result of interspecies breeding. They also lack consensus about whether a koy is a wild or domesticated animal. As we know, the rabbis like it when there are clear categories and when things fit clearly into them. The lack of clarity in this case is not only a zoological challenge but also a legal one. Not knowing if the koy is domesticated or not makes a difference to our understanding of whether the prohibition on slaughtering a (domesticated) animal and its offspring on the same day applies to it.

To account for the lack of clarity in the case of the koy, Jewish law applies the stringencies of both domesticated and undomesticated animals. That way, whatever a koy actually is, we can be sure we’re not violating halakhah. That is, if we could actually find one.

Read all of Chullin 80 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on July 19, 2026. If you are interested in receiving the newsletter, sign up here.