Why did my dogs kill a deer?

I need some advice. Hopefully, I'm just being paranoid.

I am the proud mama of 3 dogs... a 5-yr. old male 50-lb. mixed breed, a 5-yr. old female 70-lb. German Shepherd, and a 3-yr. old male 75-lb. German Shepherd mix. They stay w/ my in-laws' house on an 11-acre parcel of land in the country whenever my husband & I leave town. My in-laws have 3 dogs as well, so when the grand puppies are visiting we joke that they are quite the little "pack." All of the dogs are good with other dogs and great with people. If a strange dog comes onto the property, they may bark & run after it to chase it away, but all of them immediately retreat when called off and none of them have ever injured another dog.

Last weekend, my mother-in-law babysat the dogs. One morning, she looked out of the window into the front yard & saw 5 of them gathered around the same spot (the 6th dog was in the house... she's 14 yrs. old & doesn't partake in much anymore). The other 2 dogs involved are a 10-yr. old female German Shepherd & a 30-lb. female mixed breed. (It probably doesn't matter for the purposes of this e-mail, but all dogs are spayed & neutered). When she went out to investigate, she was appalled to find them eating on a dead baby deer that was no more than a few days old. She verbally scolded them & called them off which they immediately did. The deer's body was still warm which led my father-in-law to believe it was a fresh kill. My GSD mix had most of the blood on him & my female GSD had some on her as well. There didn't appear to be any blood on any of the other dogs.

What led up to the kill, we can only speculate. And, I suppose there is a very tiny chance that something else killed the deer before our dogs got a hold of it. But, I have the worst image in my head of this pack of perfectly loveable, obedient dogs stalking & killing this helpless baby deer. Had it been another dog, I personally would have considered this far worse, and had it been a squirrel or bird or rabbit, somehow it wouldn't have been so bad. And, had they chased it down & killed it from playing too rough, I guess that wouldn't have been nearly as bad either (since then, it would be an "accident"). But, the fact that they killed it, then ate on it seems so primal.

Now, that you have the story, here are my questions: 1) I've often heard that dogs that get the "taste of blood" will always go back. Is this a myth? 2) Is this single incident with a baby deer a sign of worse things to come? 3) Behaviorally, have my dogs done anything wrong and should I be concerned? Being a lover of all animals, this incident upsets me; but, I also realize that while dogs are domesticated animals, there are still many instinctual qualities that will always be there.

I appreciate your insight.

Amy