I've been thinking about this thread a lot and have finally decided to post something because prior to now I just wasn't sure what I would say. So here goes.
1. Any dog that has any real prey drive can be trained to track blood. Blood is actually rather smelly and easy to track for a dog - much easier than say finding a pheasant in the midst of a field. So long as the dog has any prey drive at all the training isn't too difficult. Some dogs (like mastiffs) have almost no prey drive and as such training them to track is next to impossible. That's not to say you won't find exceptions to that rule but they are rare.
2. Depending on your area you may be illegal if you track a wounded deer with a dog. In Wisconsin so long as you maintain control of your dog(s) with either a leash or they are in audio AND visual range and are controllable by commands you can track a wounded deer with the caveat that all of your hunting weapons MUST remain back at camp/vehicle. I was told by one warden that if you had a side-arm on you he wouldn't ticket you for hunting illegally and I was told by another warden that he would ticket you if you had a side-arm on you. They were both wardens in the same county. I guess it just comes down to interpretation of the law by the warden at that point in time. If you intend to track wounded deer with a dog make sure you know the laws and how your local warden will interpret that law. I'd rather lose a deer than end up with a ticket for hunting illegally.
3. Typically within the circles of bird hunters they work hard to break their dogs from tracking and chasing anything but birds. As a trainer I can say that if a dog is trained in hunting other types of animals it makes it more difficult to hunt a particular species effectively because the dog will chase after any scent he/she has been trained to hunt. That means if you're out bird hunting your dog might pick up the scent of a rabbit and go after that while you follow it thinking you'll have a bird to shoot. Worse if its pheasant season and your dog decides to start tracking a deer that he/she might have caught scent of. I've talked with people who do a lot of coon hunting and some bear hunters who hunt with dogs. Both groups say that their dogs are trained specifically for what they hunt ie. ONLY coons or ONLY bear. The reason is the same as before - you don't want your dog going off chasing a different species than what you want. Its a good idea that if you're going to have a dog that tracks wounded deer you should limit it to that and don't try to hunt other animals with it. On the bright side a dog that's trained to track wounded deer could also easily be trained to find and retrieve sheds too! Then in the off season you could go out with the dog and find whatever sheds might be in the area and have some antlers to make decorations out of.
4. Breeding is a big issue - or I should say bad breeding is a big issue in the world of dogs today. There is far too much breeding simply for cosmetic reasons and not enough breeding for actual physical abilities and prowess. True there are still breeders that breed dogs specifically for their particular abilities - the breeders that I get puppies from breed labs specifically for their hunting ability and intelligence. Police departments typically buy dogs from trainers and those trainers buy puppies ONLY from breeders that breed for those dogs' specific abilities ie. bloodhounds with better noses and a better recognition of different scents or GSD with a certain temperament that makes them trainable, brave and have enough heart to actually bite a human being on command(something many breeds don't have because its been bred out of them).
5. I don't know of any professional or semi-professional trainers that train dogs to track wounded deer in this area of the country. I've hunted with people who have trained their dogs to track and bay wounded deer on their own and they've done so to good effect. There were a few deer that we'd have completely lost after being shot were it not for the dogs.
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