Here are some Interesting facts that I learned when I contacted the Dairy Counsel customer service a few years ago:
The fat percentage from Holstein cows in NY is inconsistent, and It is also too low on fat content for ‘regular’ milk. (It averages about 2.5%.) The milk cannot be used/sold as-is. While typical household consumers might not mind, manufacturers need to be consistent.
Therefore ALL of the fat is removed from the milk, and then added back in with precise amounts to form the different types of milk. Thus, the milks are all identical in vitamins etc… The ONLY difference is the fat content.
Regular milk has 4% fat
Low-fat (aka ’99’) milk has 1% fat
Skim milk has no fat.
So if you had just regular and Skim milk in your fridge, but wanted Low-fat, you could mix 3 parts skim and one part regular and get what you need!