If anyone is curious, I did call the Tulare lab. I left questions for Dr. Chin (who did the necropsies) but have not heard from him. I talked to someone who said she was a lab tech (and, I assume/got the impression, one of his students). She said that if the e.coli was passed from the hens into the eggs and incubated there, the chicks would likely be hatching with very poorly absorbed yolks and obvious infection/mushy chick type symptoms (basically, the infection would already be wreaking havoc before they were even hatched). She said there wasn't a way they could really say were it come from, but one egg that had been contaminated with feces "could very possibly do it".
I'll let you know if Dr. Chin responds, but it sounds like the breeder just had the bad luck of something sneaking into the incubator. Still no losses among the chicks that didn't go right off. The breeder mentioned that incubator did have a few exchange eggs in it, so in my mind they just had the bad fortune to get an improperly washed egg in that batch. The batches with only the breeders' eggs haven't had these problems. They've mentioned going back to a 'quarantine' incubator for outside eggs. It's a little scary, because I know most chicken people tend to think of hatching eggs as the bio-secure route to take. Unfortunately, there is always that slight risk.
You either take it or never get any fresh blood in your lines.
All things considered, I would buy from this seller again in the future. The evidence from Davis doesn't lead me to believe their flock is unhealthy, and they've been great to deal with during the whole necropsy thing, and the chicks I have left from the batch I am very happy with.
