As we have learned, if someone steals an ox (shor) or a sheep (seh) and killed them or sold them he will pay back five times the value of an ox and four times the value of a sheep (see Shemot 21:37) as a kenas – a penalty.
What exactly is a seh?
According to Rava, the term seh refers specifically to a simple normal animal, but not one who was kilayim – a cross breed between a sheep and a goat. Rashi (in Massekhet Ḥullin 78b) says that the source for Rava’s ruling is a passage in Sefer (14:4), which teaches that kosher animals include a seh from the family of sheep and a seh from the family of goats.
Rava’s ruling notwithstanding, a baraita that appears in our Gemara teaches that the law requiring the thief pay a kenas of four time the value of a seh applies even if the animal is kilayim – a cross between a sheep and a goat. The Gemara explains that the passage that teaches the laws of kenas says, “shor o seh – if either an ox or a sheep” was stolen. Since it is impossible for an ox and a sheep to cross-breed, the Torah’s emphasis on the “either/or” aspect is understood to include any type of seh – even one that is kilayim. Admittedly, when the Torah uses the either/or terminology it is sometimes understood as excluding kilayim, but that is only if the two animals under discussion are animals that theoretically could produce offspring together (e.g. Vayikra 22:27).
Despite certain similarities that we find among domesticated animals, sheep and goats belong to the family of Caprinae, while larger animals like oxen, bulls and cows belong to the Bovinae family. This genetic difference, as well as the sheer disparity in size, will not allow them to produce offspring together.