St Bernards

Question
We have 4 dogs. 1 rottie mix ,1 GS, 1 queenslands heeler and a Saint Bernard. They 4 acres to run and explore. The problem is the SB has now taken to attcking the other dogs seemingly unprovoked.This has left my family in utter turmoil. We have taken her to the vet several times, tested for all knids of afflictions and they all come back negative. We have tried to seperate them at feeding time, and keep the peace. My wife is heartbroken about this. Short of getting rid of the SB i don't know what else to do.

Answer
Frankly, it is impossible to correct something without knowing the cause for it.

You seem to have eliminated any possible physical cause for this, although it still could be something they missed, such as something going amiss in the brain. Not common, but it does happen. Pain can easily trigger an attack and is a very common reason for this, and the vet might not have even come close to finding any pain issue yet. Did he X-ray her for hip dysplasia? (VERY common in Saints) Could she possibly have a bad tooth? The possibilities could be endless. Boy, do I know how crabby I can be when my bad back starts getting cranky!

I have a lot more questions than answers, I'm afraid. How old are all the dogs? Are the other dogs males? Females? Neutered or intact? Is the Saint spayed? Is this just a feeding issue, such as food guarding?

If this is purely a behavioral issue, there is generally some sort of provocation that triggers an attack. Pay closer attention to the dog interaction and see what is going on just before an attack. Attacks rarely happen just out of the blue. It is not uncommon for an instigator to set these sort of things in motion; some just like "getting another's goat" so to speak by prodding them until they go off. Keep a journal of the incidents, and note which dogs were involved.