Not a metaphor, it's actually a thing used nearly everywhere Rule
Did you know? Cows are very affective animals and form a strong bond with their kids, very early on.
In most farms, cows don’t even spend a day with their kids before being separated.
I knew someone who lived next to a hobby farm that would just keep a few cows. Whenever they sold one, the cows that were left behind would just moo out for the missing one days. It sucked.