This is tough,you have a Mastiff who was doing great
with all the other dogs,raised with them right(?) one had
a litter,( since you had a neighbor dog breed her by now
you've had her spayed right?) now there is a problem
and the Mastiff has hurt the puppy?
Is the Mastiff spayed or a whole female?
THE BIG THING is you have a child and the Mastiff is
growling at you son...I am at a loss because we had
a English Mastiff I was showing yeras ago and she
was a real lamb,very laid back...BUT YOU CAN NOT
HAVE A DOG THREATENING A CHILD.
Have you talked with your vet? Is there any professional
trainers you can call,most dogs don't just start to "react"
different all of a sudden and growl or change without
Puppies can be a real problem for an older settled dog,
they pester and nip and grab at older dogs but since the
Mastiff is a HUGE dog compared to the others this is
also a issue.Mastiff vs small puppy...not good.
IF she is whole ( not spayed) a vet needs to check her
to find out if there is a hormone inbalance,she could
have a vaginal infection,something has changed and
you need to find out what is going on to help her.
IF everything checks out at the vet,as much as I hate
to say it,you may need to rehome the Mastiff AND TELL
the new owners there is an issue with small dogs and
small children-DO NOT JUST LET HER GO without
telling a new owner as you don't want anyone or any
small pet harmed.
Wished I could offer more help but YOUR FIRST VISIT
NEEDS TO BE AT YOUR VET for a full check-up ASAP
and until then keep her away from the other dogs and
The fact that your Mastiff is attacking your other dogs is bad enough, but the fact that she is growling at your son is terrifying. That is a HUGE dog to have around with an attitude issue.
The first thing I would do is take her to the vet. Dogs don't just lash out for no reason. Pain is probably the #1 cause of a dog acting out of character, but if she is growling at your son for no reason, it almost makes me wonder if she has developed some type of mass in her brain that is affecting her behavior. Of course, this will be quite expensive to diagnose, as MRI or CT scan will be necessary, but if you have any hope of keeping the dog and having your son be safe you are going to have to pull out all the stops here. It would be bad enough if this was a chihuahua that was acting this way but this dog is probably larger than your 10 year old son, so you've got to be extra careful here.
In the event nothing is found upon a scan, I would contact a behaviorist and get to work. Of course there is always rehoming the Mastiff, but it would be unfair of you (and truthfully, a bit dangerous) to rehome her without disclosing all of her quirks to the potential new owner, and this will make it extremely difficult to rehome her. To just pass her off on someone else without a warning would mean that she could not only do a LOT of damage to someone else's pets or family members, but it could lead to her being mistreated and abused. And while it is the last thing we want to think of, it is for this reason that sometimes euthanasia is the only way out because that way you have closure. You KNOW where she is, you KNOW what happened to her, and you know that she is not hurting anyone nor is anyone hurting her.
If this is a mass on the brain, euthanasia is the kindest way out because her life is only going to get more confusing and violent as time goes on, which will be no good for anyone involved.
Please let us know what happens. I wish you only the best and hope that you can arrive at a solution that works for all concerned.