HELP - Resident Yorkie is aggressive to puppy
 

My five year old male yorkie has never been aggressive other than playing with us, we wanted to get him a friend and at first he was absolutely terrified of her but now if she stops playing with him he bites her hard! Today he grabbed her by her foot and she screamed for 2 minutes and has been limping since. I've tried yelling "NO!" When he bites her and putting him in the kennel for time out but nothing seems to work. I'm considering sending him to a obidiance class to learn how to socialize with Bella without being so aggressive. I don't think he's biting her to be mean, he just wants to play but doesn't understand that she is fragile. He's 9lbs and she's 2lbs.

I guess my question is does anybody have any suggestions on discipline or what I should do to make him behave?

First, I would allow them to interact only while closely supervised because of the size difference (ideally with you sitting on the floor with them). Dogs can 'play' rough during the adjustment period. I went through something similar when I brought home my second Yorkie, but he was 8 months old so we didn't have as big of a size difference.

Teddy, my younger one, is the wrestler while Max, the older one, is not aggressive. Max was a little confused by Teddy's puppy-ish ways. We had a lot of play biting of legs and backs and sometimes it would get out of hand (occasionally it still gets out of hand, usually when the boys have pent up energy).

I raised my voice only when things got dangerous, and only to get their attention, break them out of wrestling. But no yelling/anger.

I used keywords and phrases like "settle down!" and then I would make them perform a sit. Start training your puppy for general obedience, performing sits. Basic training is what helped my boys bond and learn to do constructive things together.

Having a schedule of activities also helped. They knew when to anticipate meals, brief games of fetch, and walks (which I know you can't do until your puppy is done with shots, and is ready).

I would skip using the kennel (a dog's safe place) as a time out. Instead, separate with a baby gate or xpen.

Put your older dog first, greet him first, and reassure him that he still holds his position with you.