She has gone aggressive?

ronnie has changed.
a few weeks back a man cam out of a shop she was sniffing him all fine then she looked up and out of the blue she changed got all aggressive, hackles up teeth bared and tried to go for the man, i have no idea why, then the other day my fiancee took her out with my step dad and is dog, she went upto a man and started getting funny towards him too, hackles up growling snarling and apparently went for him.

iam taking her to pets at home tomorrow to buy her a muzzle.

i just dont know why she has turned like this she has no reason what so ever and its ben the past 3-4 weeks, she is perfectly ok with my family and others she knows but this i cant understand HELP!!!!

The first thing you need to do is take her to the Vet and have her checked out medically ASAP. There are different health issues that can be associated with a change in behavour and/or character. She may appear fine to you, however this may not be the case

Once she gets a clean bill of health you need to get professional help - your Vet could probably recommend a Behavourist/Trainer

A muzzle will only mask the problem, you need help to address the problem and work on it - with help

Yes vets first.

How old is she? Is she spayed?

Did you get her spayed?
Have you had any changes in the house?
Do many people walk the dog?
Do you go training with her?

If it has just started happening (as opposed to something that has gradually got worse) I would look for what is triggering it.
In the meantime, if she looks anxious about anyone turn round and take her away from them. Then praise her when she is calm.

Could quite possibly be nervous agression is she in her teenage stage as this could be the time it starts to come out?

If it is and you don't know how to deal with it i really would go for the behaviourist. I can recommend an excellent one who also owns Rotts who i'm sure will travel to Essex.

My Rott can be nervous aggressive but nowhere near what you describe and i've dealt with it myself and she is much better than she was. She is 7 now. The muzzle is an excellent idea and learning to read you dog is vital.

ronnie is 15 months old, she's not spayed either as i was going to breed from her but due to this i am now going to get her spayed.
i am going to ring my local trainer he owns blackwater dog training center in essex he is the nuts, lol i will ring him today if i get time.
I do feel getting a muzzle today is the right thing other wise i cant let her off the lead it is also when she is off the lead that she gets aggressive as well.

You shouldn't let her off lead wearing a muzzle. I wouldn't be letting her off lead anywhere until you get the problem sorted out

No disrespect Dawn but i really wouldn't let her off the lead muzzle or not if she's that bad.

You're most certainly doing right not breeding from her.

This"aggression"could be hormonal linked to her season

There are many possible causes for this behaviour but I wonder if the fact she has reacted badly to men is significant. If the dog does not encounter men often it could be just she's saying...keep away I don't know you.

If that is the case one approach is to habitualise the dog in a controlled environment with lots of men who are confidant around dogs. A good trainer/behaviour expert will help.