Perhaps barn raised litters have a higher percentage once they get used to them.
I believe that is a key point.
Barn raised kittens are taught by their mother - who relies on her hunting skills to
survive.
The natural instinct is still there for kittens raised in a cozy section of a warmed home.
However, it is probably not 'hammered home' in the same manner by a spoiled 'lap cat' who grew up on cans of 9-Lives.
The same general principal can be applied to hatchery raised chicks.
If they always have a feeder full of "Chick Raiser" in front of them, they may ignore their natural instinct to forage.
If you throw them a clump of weeds (complete with insects) every day - from 1 week old, they learn to forage.
Natural instincts are always there, but can be over ridden by complete domestication:
I have seen a photograph of a mother hen, and under her wings were a half dozen chicks, AND a baby mouse!
Perhaps, the 'mothering' instinct is stronger than the 'foraging' instinct.
I would imagine that none of those chicks will ever catch/eat a mouse.