Ricki Carroll must only be referrring to one breed of dairy cow - most likely the Holstein Fresian. The Holstein would average about 3.8% butterfat, maybe. In NZ the Holstein probly averages a tad more - maybe 4.2%
Generally all other breeds of cow would be higher with Jersey being the highest.
It depends on what they are being fed too.
Here in NZ on our all grass based system, we have 450 cows of mostly Jerseys, but there is Fresian,Ayshire and others.
Our current butterfat test is 5.8%, this will rise in the next few months as they progress with their preganancies, should peak at about 7%