There is two schools of thought on this. One of which says it is genetic, and the other says it is nutritional/environmental.
I have to split these opinions and say I honestly think it is a combination of both. IF your cattle have the "bad hoof gene", then any nutritional or environmental problems will be exaggerated by showing signs of split and/or cracking hooves. On the other hand, if you have good structure and "good hoof genes", then they will be better able to handle the environmental/nutritional problems that are in their surroundings, thus, they will not show signs of damaged hooves.
If you think it is nutritional, draw blood and have them tested for mineral levels... but at this point, I would suspect you have the "bad hoof gene" along with some environmental problems such as really hard ground, lots of rocks, or very wet ground (makes the hoof soft). Many times if you change the environment you will improve their hoof condition.