I would imagine it's still while milk. From what I was told, the process creates smaller fat particles that are easier to digest for babies/infants as well as being better for cooking.
All of our milk is whole with the exception of 2% and skim. Our whole milk can vary on the butter fat depending on the time of year. For example, right now its winter an the cows are eating like crazy so our butterfat is really high (averaging 4.5-5%). In the summer the cows are drinking much more water at the butterfat definitely drops (averaging 3.6-4.2%).
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