Complex sentence: In the United States, the giblets of chickens, turkeys and ducks are much more commonly consumed than the organs of mammals, except for the liver, which is common to a certain degree.
Split into simpler sentences: In the United States, the giblets of chickens, turkeys and ducks are much more commonly consumed than the mammal offal. Use of organs of mammals is not common, except for the liver, which is common to a certain degree.