When I first adopted Reagan, she would constantly try to hump my female lab. She never did this to my male lab mix, but for some reason she did it to the female. She was over a year old when I adopted her. She has since stopped doing this, not sure if she stopped because of me correcting her or if she just doesn't want to. I think it was a dominance thing.
Anna, dog-mom of:
Reagan: rescue GSD
Bandit: rescue lab/hound mix
Didi: black lab/guide dog drop out