my 7 month old female yorkie is fighting with my 6 month old maltepoo

Question
I recently brought home a 7 month old Female yorkshire terrier. I already have a 6 month old Maltepoo (maltese poodle mix.) Anyways, from the first day since we brought home the yorkie, our maltepoo has been really aggressive with her. Not to the point that he's hurting her though. He's just really playful. He's been sniffing her private parts alot, in fact every chance he gets, he smells her there. And when he does that, she snaps and growls at him showing teeth. I'm worried because she's only 4.5 lbs and he's 13.5 lbs. Big difference. Could she be going into heat and that's why our male dog is always after her "private parts?" He's also showing signs of wanting to hump her, he tries to grab her with his mouth at her neck as if to hold her in place. She fights back. Please help. I need to know if this is something I should be worried about and if so, maybe it is not in her best interest for her to be with our family.

Answer
Lynn,

If your male is not fixed (sometimes even if they are) he is going to go after the female whether she is in heat or not.  What is going on right now I would say is typical when there is an established dog in the home and a new one comes in.  In nature there is always a pecking order.  When a new dog is introduced to the home the residing dog has to let the new dog know who is boss.  The pecking order is not established by size but by an unspoken order that all dogs understand.  I have a 3 pound Yorkie and when I brought home a lab/Australian shepherd mix the first few days were nerve racking.  The pecking order was established in about a week and the little Yorkie was the boss of the 60 pound mix!  

There can also be a little jealousy problem going on.  You need to put the Yorkie in a crate for a time out and make sure that you pay special attention to your other dog.  As far as her showing her teeth and snapping she is just letting him know that she will not be bullied.  Her letting him know how far is to far is all part of the pecking order process.

If you had brought home a male dog I would probably be concerned.  Same sex dogs often fight (usually more the males than females)and they can fight to the point of death.  I do not think that you have anything to worry about especially since you said that he's just being "really playful" but I would keep an eye on them just in case things get out of hand.  If after a week however, things have not settled down you may have to consider the fact that the two dogs are going to be incompatible.  I have know several cases where a new puppy has been killed by the older (or larger) do because they just didn't get along.  

Something else you need to consider is that even if you get your male fixed, having a female in the house is going to cause him to "mark his territory" all the time.  You may not have noticed yet but he is probably lifting his let and peeing all over your house.  This will not stop.  A male is a male and if there is a female around it does not matter if he is fixed (or her for that matter) he will continue to mark his territory.  They do have doggie diapers that you can get at most pet stores that would solve that problem but you have to ask yourself, do I want to be putting diapers on this dog for the next ten to fifteen years.

I understand how you feel, it can be nerve racking worrying every second what they are going to do to each other but as long as you keep an eye on them and separate them if they get to aggressive you should be fine.  I hope this has helped put your mind at ease.

Sincerely,

Melinda