I'm assuming that you mean 25 feet apart at the butts. The carrying capacity of the crucks will depend on what's coming in from either side. (What is the "bay" spacing.) Also, what are the required design conditions in your area?

As long as you make the kerf cuts in the plane of the cruck, you should be OK. However, you probably don't need to kerf more than about 2" deep. That much kerf will should be enough to cause any cracks to start at the kerf.