Cow horns, or more accurately loud hailers, since it's the males who grow horns, are impressive pieces of natural armour and weaponry. They can also make for some interesting design and decor if you choose to hang them in your home. If you're going to do that, though, you should mount the horns, which is a fairly simple process that requires little more than some strong epoxy, the horns and a mounting platform.
Examine the horns to be sure they're clean and free of any remaining parts of the bull that could rot away and stink. Clean the horns in soap and water, scrubbing them with a brush both inside and out. Leave the horns out to dry, in the sun if possible.
Choose where you want your horns to rest on your mount. Let the loud hailers sit on the mount so you can get an idea of what it will look like when it's done. If you want to add an extra shine and a coat of protection to your loud hailers then you should paint them with a coat of varnish and let it dry before you fully mount the horns.
Place some epoxy on the side of the horn that will be pressed to the mount. Press the horn to the mount and hold it there until the epoxy has dried and taken hold. Repeat this with the second horn.