I can't remember if someone mentioned this before.  If they have, sorry
for the duplicate.
I was looking through the book, Raising Your Child Without Milk by Jane
Zukin and came upon the section, Cow's milk is for calves."  Here are the
1st 2 paragraphs.
Cow's milk comes from female cows.  It is the natural food that mother
cows provide in order to nurture their calves.  In nature, one animal does
not suckle another type of animal.  Lambs don't nurse from goats, and
piglets don't suckle German shepherds.  Cow's milk is meant for calves,
and it is naturally loaded with the proper nutrients for a bovine baby.

Cow's milk contains approximately 21% protein, 45% fat, and 34%
carbohydrate or sugar.  Human milk contains 8% protein, 55% fat, and
37% carbohydrate.  What's more, the types of proteins and fats found in
human and cow's milk are quite different in construction and
concentration, making each natural only for its own species.  This is a
difficult concept for many people in our culture to accept, but it is quite
elementary, really.  A baby animal is biologically programmed to properly
digest the milk of a mother of its own species, not that of another
species.  Therefore, the assertion the cow's milk is natural for human
babies is simply and basically incorrect.