done it with all my dogs, we are kinda required by law to have access to a dog that can track wounded animals, my dad does it for the police department.
we had a gs/labrador mix that was out of this world. he would "catch" and kill them to.
start small and when they are comfortable increase the difficulty,
after a while in training you can substitute the blood for water that have had deer(or animal of your choosing) hairs soaked in it, boil the water with the ahirs in it.
be sure to have a hoof or small bone of the animal at the end of the track because that is the reward for the dog.
and if you have an already dead animal let the young dogs "find" it and tug at it abit, creates an interest.
sadly this practise is dying over here because the wolf is coming back big time, we don't really dare let our dogs loose anymore in many places