Sounds like Bella is being a herding dog, with the sniffing and nudging. She sounds very tolerant and careful of her new friend. Belly-up means they are not dominating one another, or if they are, the belly one is wisely being submissive. All natural and good.

So probably the puppy will overstep her bounds, as puppies do, biting too much and too hard in play, and Bella will, as good mothers do, correct her with a growl or snap. This is how puppies learn to play without hurting. If the puppy were with other puppies, her littermates would yelp when they are hurt (which is what you should do if she gets mouthy with you).

Bella is setting a good example to the pup, and that will help the pup learn appropriate behavior and be a good dog, like Bella.

Always supervise puppies, though.

Thanks much. I feel a lot better now. The massive size difference worried me most but I will give Bella a little more leeway to be a mother as it sounds as though it will be better for the puppy.

I agree with elly, but I don't think you should underestimate the accidental injury that could occur due to the difference in size. Small breed puppies can be extremely fragile and little legs are easily broken and difficult, as well as, expensive to repair. I would be careful not to let the play get out of hand and never leave them unsupervised.

I usually split them up for a while if they get too excited. With Bella still being a puppy I think she often forgets how big and strong she is compared to the smaller dog. I do love to see her playing and having fun though.

would not stress about your dogs, what you describe is Bella TEACHING the puppy who is who and that she is dominant. Unless they are actually going at it, and you will be able to tell becasue a "real" fight will sound different, and in that case, grab the back legs of the aggressor and remove the dog from the fight. Play fighting is very important in a puppys development and to stop it is to start a neurotic dog. Your aussie is doing what she was born to do, follow the pup step by step is part of their herding instinct. Lots of leash walking or running on a fire road or at the park or the lake and you will have even happier puppies. Good luck

It is tricky - on one hand, you do want to be very careful. My mom's Westie suffered a broken leg while playing with the neighbor dog (a very nice, but rambunctious Lab).

On the other hand, I agree with everyone who said that Bella is teaching the new pup valuable lessons about how to behave around other dogs.

My terrier puppy's "best friend" is a Doberman mix shelter rescue, Violet, who was surrendered for being aggressive with other dogs. So I was very nervous about letting them play together, especially when my puppy was very young, but so far they have played together for months with no problems whatsoever. What helps, I think, is that Violet is much, much faster than my puppy, and it seems to me that when she tires of rough play, she either races around, knowing my puppy will never catch her, or comes to the door to be let in. I don't let them play inside, just in case my puppy might be able to corner Violet, and I think having her play with an older dog has been a really good experience for her.

So let them play, just be careful!