If you have never used a donkey to break calves before, you are asking for one H*** of a mess! A good donkey will only help a calf learn pressure and release, you still have to do all the ground work. We used a donkey for a few special cases, and he did the job well, but he knew the drill. He was an intact jack who was used to break Percheron colts to lead for 10 years before we got him. I would never recommend an inexperienced, intact jack as a breaking donkey. A good calf breaker has to be dead calm, and not loose their cool, ever.
I recommend you find someone in your area who has and uses a donkey. Most steer jocks worth their salt will have a donkey in their pasture. There are plenty of people out there who use them and know how to properly, don't risk a major mess when it is easily avoidable. Not trying to be harsh here, but I'm assuming you are a beginner, and this whole thing sounds like an excellent way to get hurt! :2cents:
PS. If I'm completely wrong on the beginner thing, feel free to read me the riot act. And if you are willing to post your location, I may be able to point you in the direction of someone who could help you with this endeavor.