Do You Have Any Information On Parvo?

It is a well known fact in veterinary medicine that the "black and tan" dogs like Rottweilers are more susceptible to parvovirus.  Many veterinarians extend the puppy series in these dogs to give them as much protection as possible.  Reputable breeders should be aware of this as well.  They will take steps to vaccinate early and keep parvo from their kennels.  It is a disease that mostly affects young dogs and puppies 1.5 years and younger though it can be seen in older dogs.
It is very uncommon in a 3 year old dog that has been appropriately vaccinated.  Unfortunately no vaccine is 100% effective.  It also depends on the immune system of each individual to react appropriately to the vaccine.
Please discuss this further with your veterinarian.  Your veterinarian will appreciate the feed back and may make changes to their "puppy talk" discussion with other owners of the "black and tan" breeds.  I hope your dog is doing well.

Unfortunately dog breeds are just like the human race, some are more susceptible to diseases then others.  It is all in your genetics with humans  and lineage as far as dogs are concerned.  It is very frustrating, because vets are like physicians they each have their own opinion and method of treatment.