What cardinal rule of slaveholding does master Thomas break, proving his meanness in chapter 9 of the narrative of the life of Frederick

The cardinal rule of slaveholding that Master Thomas Auld breaks, proving his meanness in chapter 9 of "The Narrative of the life of Frederick", is not giving his slaves enough food to eat. His slaves had to arrange food by stealing food from neighbors or begging for food. An example from the text which supports this is Douglass' comparison between horses and slaves where he says that at least horses get enough to eat.