Did a quick search, and antlers do contain marrow. Marrow isn't blood, but it produces blood, so I'd think it may decay inside the antlers over time.
You could try letting them sit in a bucket of water for a few weeks and test the water occassionally to see if there are any ammonia spikes.
How old are the antlers? If you've had them for a long time, it's possible everything that's going to decay is already gone..