The milk is produced for the calf.  It is very specifically tailored to
be the sole sustenance for a calf.

The muscle is similar to all flesh, not optimized, and therefore less
likely to give carnivores problems.

Human milk contains a great many substances that go through the infant's
intestinal walls and help the infant build up immunities. Doesn't it
stand to reason that cow milk contains these, but specific to calves?
And might these be some of the "alien proteins" that Neanderthin talks
about?

--Richard