Kilayim 1:6

Animal species that are similar but still kilayim with one another include: wolves and dogs; wild dogs and foxes; mountain goats and sheep; horses and mules; mules and donkeys; donkeys and wild donkeys.

Kilayim 1:7

We are not permitted to graft two different species of tree, two different species of vegetable, or a vegetable with a tree. Rabbi Yehudah permits grafting a vegetable with a tree.