Kale is bountiful with its seeds; actually, most veggies are, once you let selected plants complete their life cycle. It's pretty astounding. Hundreds of seeds, at least, from one plant.
The kale stems become quite thick and woody. Once you decide to remove the plants, ask around for a rabbit rescue organization, or inquire as to whether the local humane society accepts rabbits for rehoming (mine only deal with cats and dogs). There are two bunny rescues within a 10-minute drive of my house, and they *love* getting organic kale stems/trunks. (Mine are approx. 3 cm / 1.5" in diameter when I pull them.) I cut them into 20 cm / 8" lengths, wash them off briefly (= rinse with hose), and take them to the rescue.
Rabbit chew toys! Yummmmm!
Sunset Zone 17, USDA Zone 9