1Yr old Pug has turned aggressive

Question
Hi, my problem is my partner and I have a pug bitch who's recently turned 1 and also very aggressive!

We've never had any problems with her before and she's preformed excellently in obedience and agility training however in the last few weeks she has decided to become a menace to herself and other dogs.

Only the other day we were at out usual agility training class where she went for another dog, a pup about her size, we moved her away and thought nothing of it but later that day in the park she attacked an Alsatian who bit her and shook her, fortunately she was ok but we took her home straight away.  Now again today she has attacked a Labrador again seemingly unprovoked.  The strange thing is she does not go straight for them...she is quite happy to play with them for a little but then it's as if something inside her snaps and she starts frothing at the mouth.

People have obviously started avoiding us in the Park now and I'm very worried that she seems to show no fear towards much bigger dogs who could do her serious injury.

I can't seem to find her trigger either, she was spayed about 3/4 months ago, her diet has not changed, and she's always been a very happy and social dog in the past.

Any help or advice you could give me would be greatly appreciated as I'm so worried for her and I have no idea what to do.

Thanks

Answer
Wow!! She is obviously well trained since you have her in obedience and agility.

I am wondering if you have had her to your vet to be totally checked over. Since she is playing and then snaps, I wonder if it is pain that is making her snap.

The only two things I can recommend is to have her checked over by your vet and always keep her on a leash so that you can pull her back if she gets aggressive.

I am sorry I can't be of more help. Please let me know what you find out from your vet.

Thanks and the best of luck.