Prey drive can be a powerful force in some dogs. It can cause them to be reactive and on occasion, uncontrollable, and it puts wildlife, other animals and your dog at risk. Dogs, especially larger ones, are easily capable of harming or killing animals like deer, but dogs are also at risk of being injured or killed themselves. Not only from wildlife defending themselves, but also from car traffic while in the pursuit of an animal.
If your dog has a high prey drive you should take preventative steps to ensure you have control of your dog at all times. Work on your dogs basic obedience, in particular recall, to ensure you have control over your dog even in the presence of high level triggers such as deer. Work with a trainer to desensitize your dog to motion triggers and reduce predatory drift, and keep your dog leashed if you are not completely confident in your ability to control your dog off leash.