Nancy, slashing the top of this bread is optional. If your loaves cracked while baking it could be that they needed to be proofed longer. Once the loaf hits the oven, the yeast produces its last burst of carbon dioxide gas. This is called "oven spring." If the loaf is not proofed long enough, there is more gas than there should be and the gas finds the path of least resistance resulting in a side crack or top crack.  

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