I assume you are needing to slaughter cows for realz.
In that case, between .22lr and 9x19mm, and assuming a headshot, I'd go with 9x19 hardball. Study cow brain location to make sure the shot will be able to do it's job and press the muzzle against the skin when you fire (that way the gasses from the shot go into the wound channel and do additional damage).
If you'd prefer a rimfire get a .22magnum. Even with solids a .22lr won't reliably penetrate even a pig's skull enough to effectively stun the animal.
Whatever the case, stick the animal immediately after shooting to ensure that it dies before any possibility of regaining consciousness if the bullet failed to disrupt enough brain tissue to kill the animal outright.
Don't forget to collect the blood for blood sausage.