Q. My unfixed grown male dog is slobbering and trying to mount my new male puppy. What's that about?
JESSICA L DESROSIERS
A. Mounting behavior can be both a sexual thing in dogs, or a behavioral one. If both dogs are male, it may be that your older dog is trying to establish that he is the boss of the house by trying to mount your younger one. Stopping the behavior is best to prevent any fights from breaking out. Both female and male dogs can do this to each other, and spay/neuter status does not usually play any factor if behaviorally related.
If your younger dog is female, or not spayed, and is about 6-7 months of age, it may be that she is coming into her first heat and your male is very interested in her. Dogs should not be bred during their first heat, and if you do not wish to have puppies in the future, one or both dogs should be fixed.