Dog showing aggressive behaviour after getting second dog

our dog has started to become aggressive with other dogs since getting a second dog.

they are not aggressive towards each other at all.
it is my older dog that is showing signs.

he doesnt run and lunge or seem to go to bite just seems to walk up to them and when sniffing the other dog he growls and runs

i find this a bit odd becuase he has been extremely good upto this point with other dogs wanting to play will everyone he passes.

it also doesnt seem to be everydog we come across only some and i think mainly male dogs

my second dog is female do you think he is getting protective of her??

Is he entire?

How much training have you done with him?

How old are they both?

What does your trainer suggest?

rune

Maybe take them out seperately to answer your "is he protecting her"

If she is entire and he is or isnt he could be.

Our neutered male tries to protect our entire female. He's always been dog aggressive (unless we introduce each dog slowly) so whenever we have him and Sadie out at the same time he goes balistic towards other dogs, thankfully before we introduced Sadie I got him to a relativley calm stage where he would just grumble and look at the other dog - this compared to the full on lunging, barking and growling he used to do before. He also seems to have dragged our pup into this mess, excpet I beat him to it and the pup was socialised seperatley with our female who showed him how to act...but I'm rambling.

Yes is the answer he could be protecting her, when he growls at another dog, turn and walk away (with him on leash) and then bring him back - you will need a non reactive dog to practise with. Repeat this until he doesnt growl, if you do this without the female first then once he has stopped growling, bring the female in and go over the same exercise, praising when he doesnt growl. He should get the message however I'm not an expert and I would certainly go to a professional to get an evaluation

well hes well socialised since we have had him he was locked in a shed from a pup to 3 months without any real humen contact and only ever saw his mum and litter. he has been around many dogs since we have had him at the woods but also having friends dogs over to our house and visa versa. he has good recall and does like to play run around with other dogs when they get on. like i say its not every dog we meet it seems to be quite randam to be honest.

he is has been done and the female has not .she has not yet had first cycle as only 8 months old but will be done after this cycle has finished (currently going through this now but slight aggresion was shown before this).

he is 2.5y old she is 8 months

I am having the same issue with my 15 month old neutered male havanese. We have his brother (different) litter who is now 5 months old. He has become aggressive at times with us, mainly over territorial type issues. The trainer says we have to re- establish dominance over him as he thinks the puppy is his property. It seems to be working.

you arent having the same issue.

the OP said their dog is difficult with other dogs, not people

'establishing dominance' doesnt mean anything

Please find another trainer ~ one that doesn't resort to the discredited & silly ideas about dominance.

Have a read of this article which gives you much better & scientifically correct information (& better stll, perhaps show it to your trainer ). http://www.dog-secrets.co.uk/why-wont-dominance-die/

i agree

the dominance theory techniques will work, but its possible they can only propogate agression in the long term. Also, incorrectly applied, which is entirely possible, they will make matters worse in the short term

also, i switched away from these techniques a few years ago and found that i am personally much happier with my dogs and my dogs are better too

anyway back on topic....

i would go with the above, walk them separately to find out if its guarding the other dog and also use rewards when around other dogs, otherwise the agression will escalate

What do you mean - the bitch is going through her cycle? Do you mean she`s in season? Or is around the time of her season?
If so, your answer is staring you in the face.
If not, I would get the dog vet-checked - I assume he`s getting more exercise since the new girl arrived and he may be feeling it.
If he is fine, I would simply go back to basics with training and work on recall for when other dogs approach.
Shamus gets upset when some dogs approach Daisy, but I just call him to me and he is content. I have absolutely no idea what`s in his mind - if anything, but I don`t think that matters.
Re dominance - it`s a made up theory by people who know little about animal behaviour but want to make money out of the gullible.