Kinetic energy alone means nothing.

What kills the animal is how the object transfers the KE to the animal and the amount of time it takes to transfer that energy.

It's like the old saying... "Speed kills".
No it doesn't.
The rate at which speed changes kills.


To answer the question the minimum amount of KE depends on the bullet being used. A suitable bullet could be coming from a 223 Remington or a 45/70.

Yes the number would change if we were talking about a 20ga slug vs a lighter weight lesser constructed bullet.

I would want about 500 foot pounds of KE from a rifled 20ga slug on the deer at about 100 yards. Which the 20ga slug would have in spades.