Why on earth did my 5 year old dog go for this puppy?

[hmc]

I am really disappointed in my Bernese Mountain Dog. Her temperament is thus:

• used to be nervous around people as a pup, but now always confident. Loves people and is soppy with them

• bit of a hunting instinct - did rip the head off my cockerel when she got in the back garden once , and has gone for piglets left to graze freely in the New Forest

• 99% good with other dogs. Runs over to other dogs off lead and greets them enthusiastically. Perhaps one or two times has growled at another dog aggressively (when they have growled at her first)

So I am a bit gutted that when I introduced her to my friends 4 month old chocolate labrador (who was on a lead so not bothering her) she bared her teeth, her hackles rose, growled threateningly and looked as if she would have taken a chunk out of him if I had not jerked her back.

Why would she do this? I'm gutted because I want to share dog walks with this friend but it looks unlikely now

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I don't think anyone can give you a credible answer without having seen the incident and without having seen and assessed your dog, hmc.

Where was she when you introduced the pup to her?

She was in a location where she regularly gets walked and meets many other dogs off lead, usually without event

Out of interest was the Labrador being very bouncy? I have found older dogs seem to get fed up very quickly with my bouncy lab.

Either way it is just preservation really walk them together but on leads ensuring neither dog can come to harm. I had this problem quite a bit with my mum's dog. We kept trying giving treats in each others presence while ensuring them could not harm each other and now they are fine still not 100% and have to be kept on a lead together.

Not especially BigN - lab was on a lead.

Even so my Lab can still bounce on a lead and older dogs don't seem to like it. But then when I am 80 not sure I would be to happy to be clambored over by a teenager .