Cow skulls are MUCH thicker than deer skulls, which is why the device they use for killing cattle leaves only a very small puncture wound on the animal (as it shoots out at a very high velocity). It would take 12+ whacks with a metal pipe to kill a cow, which would only torture the poor animal.

If you're interested in seeing what they use, watch "No Country for Old Men." The CO2 powered device that Anton Chigurh used is something used in putting down cattle.

Anyway, I would notify the owner as soon as possible. Unless you have a revolver, I wouldn't chance putting down a cow with a small caliber hand gun, even if shooting through the eye. It might not kill it right away.

Don't use a pipe, use something high caliber (either a powerful hunting rifle, a revolver, or another high caliber handgun). Otherwise, you're bound to inadvertently torture the poor animal worse than it already has been. A pipe would not work.

Honestly, the quickest method might be to find the owner as soon as possible and have him put it down.

[DISCLAIMER]

If an animal is injured, contact the owner or a nearby neighbor as soon as possible before doing anything else.

Even if the animal is terminally injured, you're not a professional, nor the owner, and it is up to them to make the decision on what to do. Even though the injury is horrific, always stop to think and talk before deciding a course of action.

Remember... Deer are wild (usually), so putting one down with a pipe is different than killing an injured animal that someone owns.