Aw... so sad to hear stories of chicks killed by dogs. Our elder dog is now starting to show Livestock Guardian behaviors with the chicks, following them around and (maybe) beginning to ensure they're staying together. And this new one seems to be getting better -- we are taking her out at the same time as the chicks are out and observing closely, so we can correct her if need be. She has chased once (seemingly wanting to play), but nothing since. She's also turning to the older one for guidance. Fingers crossed.
As for the "taste of blood" thing, I have read lots of stories of people having trouble with their dogs, but then being able to train them to leave the chickens alone. That would seem to go against the "taste of blood" theory. I tend to think that some dogs are just more difficult than others, because they have more of a prey instinct. Wish me luck with ours. Best of luck with yours!