Mounting behavior in our dogs is embarrassing to us because we automatically feel uncomfortable with the sexual connotations. But to animals, this is just another behavior in a long list of behaviors, like barking, staring, or laying back ears. These motions are an expression, like our words. There are words that we choose not to use because they carry embarrassing or emotional stigmas, but your dog does not have the same cultural norms or expectations in the way he expresses himself as we do. Each of a dog’s behaviors carries meaning, but it is not necessarily the meaning that humans think.
Mounting can be sexually driven but doesn’t have to be. Just like your dog might growl and shake a toy during play, he may also mount the toy. Play tends to be a reflection of actions in normal life, maybe even a rehearsal. We know that play behavior is important to good mental health and growth.
Dogs do not have any emotional feelings about the gesture nor do they feel any awkwardness about it, like people do. When it is driven by hormones, as in an intact male, it is more likely to be sexually based, but neutered males and females can engage in this conduct as well, and almost all puppies do too.
There can be other reasons for mounting too. It can be a manifestation of stress or excitement. It’s almost like the dog or puppy does not know what to do with himself and tries different behaviors. It could even be an attempt to self soothe, like thumb sucking in humans.
No matter what the motivation, if it is a behavior that you would like to abolish, you can distract the dog with a substitute action that he will know earns a reward. It is important that you seem oblivious to the mounting though, and act as though the alternate behavior was a spontaneous request.
It helps to know that there may not be any sexual motivation behind the motion, even though it is embarrassing. Just like any behavior, dogs can learn an alternative action if you are patient. Reward the things that you want to see happen and ignore or distract from those you don’t.