I have a 7 year old entire male labrador who, up until about 6 months ago, has always been the most laid back dog you could ever wish to meet.  However, over the past few months, he has become agressive towards every other entire male dog he meets whilst we are out.  His whole life, I have always shouted to oncomers with off lead dogs, to check they are friendly and then allowed him to sniff, play etc, but now I always call him close because I know, if it is an entire male, he will immediately go tail stiff, hackles up, growl and then quickly go for the other dog.  As yet, he hasn't actually bitten a dog and damaged it but it is really beginning to put me on edge during walks, and my 11 year old daughters no longer wants to come on walks as she is frightened.  As a bit of extra background info, he was attacked about 2 years ago, by a dog which ran and grabbed him straight by the throat with no warning - but he didn't become aggressive immediately after this.  A year ago, we got a cairn puppy (bitch).  She is spayed and it doesn't seem to be linked to her (i.e. he will react whether she is with us or not.)  I would be so grateful to hear from anyone who has any suggestions as to why he has become this way?  Is it his age?  or something else?  And for any suggestions as to lessening this, or dealing with it. 

Has he had a health check recently? I'm wondering if it could be hormone related as it has come on so suddnely and without any obvious incident.

My boys the same due to the same thing, plus it didn't start straight after the inicident and was about 2 years later.  I now can't have my other boy here and they lived happily until the girls were due to come in season for 5 years, last year unfortunately my boy decided enough was enough and he just hated poor Lastar.  Thankfully my parents took Lastar on, though as he's almost 11 he's of course no trouble.

Anton does down when off lead if I shout him when another dog is coming.  He will then stay there and if the other dog is friendly then off they'll go and play.  It's really weird as he's not an out and out nasty dog. In fact temperament wise for the breed especially with people he has one of the best termperaments.  Unfortunately though I can't help you, the only thing that has helped is ensuring control, putting him on the lead and for him to see that the other dog is friendly.

Many thanks for both replies - perrodeagua - your approach aounds just like mine - it's just such a shame isn't it, when walks have been stress-free and turn into this :(  Lucyandmeg - really interested in the healthcheck, and will book him in for one this coming week, thanks :)However I am always a little bit wary of my vet as every time Dylan goes e.g for yearly vaccinations he likes to mention castration.  This was something we opted out of long ago as, after lots of research, we decided not to go for it, mainly because Dylan had never showed any signs of being aggressive!!!!  BUT, if castration is a possible solution, then I'm fully prepared to consider it - has anyone else had experience of this resolving a problem like mine?

> BUT, if castration is a possible solution, then I'm fully prepared to consider it - has anyone else had experience of this resolving a problem like mine?

NO!
And, stick with the decision you made when you did your research.  You found no good reason to have your boy castrated then, so don't doubt yourself.  As to vet always mentioning it - yeah I know!  So glad that mine has realised that it falls on deaf ears!

I don't think castration is going to resolve the problem, and think you would regret it.

I agree. Chuck was everyones friend until he was castrated. Now he has to defend me and himself (what a shame) mostly bravado and gets a shock if the other dog retaliates.

> BUT, if castration is a possible solution, then I'm fully prepared to consider it - has anyone else had experience of this resolving a problem like mine?

Instead of castrating him in the "hope"of it helping have you considered the Suprelorin implant-the effects last for at least 6 months & give you a non invasive choice to see if castration will resolve the problem

Again, many thanks to all for your replies - it's nice to know I'm not alone and sometimes that reassurance is all that's needed :) .  I googled the implant and found some discussions (on a lab forum no less!) where the effect was found to be similar to castration i.e. timidness or aggressiveness only enhanced :( but I'll keep reading up on it.  He's off to the vets on Wed for a health check so we'll see what that raises, but so far, it seems a good handle on him is the way forward for the time being.  It's been really informative hearing all the approaches, I'll keep you posted
Zoe and Dylan (fast asleep snoring in his bed like the sweetie he really is!)

> we decided not to go for it, mainly because Dylan had never showed any signs of being aggressive!!!!  BUT, if castration is a possible solution, then I'm fully prepared to consider it - has anyone else had experience of this resolving a problem like mine?

our behaviourist is in two minds about castrating our boy and so has decided not to. tio is fear aggressive and he says that removing his source of outgoing nature would be a bad plan and make him worse. so depending on whats up with your boy then then it might make things worse.

> where the effect was found to be similar to castration i.e. timidness or aggressiveness only enhanced :-(

That isn't my experience the effect mimics castration exactly, except for the fact that if it doesn't have required it can be reversed by not renewing the implant  unlike castration which cannot of course be reversed

>> where the effect was found to be similar to castration i.e. timidness or aggressiveness only enhanced
>the effect mimics castration exactly

Isn't that just what Dylanandlola said?

Nope

"I googled the implant and found some discussions (on a lab forum no less!) where the effect was found to be similar to castration i.e. timidness or aggressiveness only enhanced"

My experience first hand is that the effects mimic castration exactly without any enchancement

I read it as saying that because castration (as borne out by plenty of anecdotal evidence) also enhances timidness and nervous aggression, the implant has exactly the same effect.