Almost certainly just the fat percentage. It's common for cows to produce milk at notably higher fat percentage (often more than 5%) than the mandatory minimum

Almost certainly just the fat percentage. It's common for cows to produce milk at notably higher fat percentage (often more than 5%) than the mandatory minimum standard for "whole milk" (3.25% in the US) that large commercial producers centrifuge and re-blend down to to maximize profit. Most consumers are unaware that "whole milk" is a specific commercial regulation that does not mean "all the original milkfat", and this gets in the way of educating people about the danger of drinking milk raw. Add a bit of pasteurized cream back into your pasteurized milk and see that it tastes much better.