Or HaChaim on Exodus 21:37/אור החיים על שמות כ״א:ל״ז

1 וטבחו, or he has slaughtered it, etc. This refers to either the ox or a sheep. Should the stolen animal be a lamb or a kid and the thief had to raise it in his home so that it turned into a different category animal, i.e. a fully grown one, he is not liable for this five or four-fold payment, seeing he had become its owner by the twin method of shinnuy reshut u-mekomo a change of both domain and place (home). This is the thrust of the comments by the Talmud in Baba Kama 65.

2השור. the ox. In the Mishnah Baba Kama 62 it is stated that only the two categories of animals mentioned here ever qualify for the four or five-fold compensation payable to the owner. The reason cited there is that if other animals were included in that legislation the Torah should have written the words "and he either slaughtered it or sold it," immediately after the word שור instead of waiting until both שור and שה had been mentioned. As it is we deduce that either one of these two categories is meant exclusively. The present wording excludes both other categories of animals as well as the same category of animal if it had matured in the hands of the thief.