I've never heard anything bad about giving them veggies. After all, they eat vegetable matter exclusively. I don't really know what kale is, but if your horse likes veggies and eats them, give 'em to him. I know a lot of trainers use carrots as treats, so you may want to try that. I think, though, that since horses eat only some form of vegetable matter that feeding them the ones we prefer shouldn't have any ill effects on our fuzzy friends. If he seems to push the pulp around a lot, I would suggest giving him the whole veggie instead of the mush. If you have more in depth questions about what veggies are good for them, I can look up some sites that might be helpful and post the links here. I need t figure out links here anyway.