It may be a coccida the vet was referring to. Because dogs will consume feces or other species, they may have spurious oocysts in their own feces.
They don't get the infection but the indications of the parasite show up as the rabbit feces pass through the dog's system.
Or it could be clostridium
which is in a lot of dog's systems without causing any issues.
Hope this helps you!
Yes this is a form of a yeast type organism that typically lines the intestinal tracts of domestic and feral rabbits, guinea pigs and mice etc and that when their population is high enough end up being in the droppings of those animals it typically causes diarrhea in young animals.
I did find a case where this was an incidental finding in a dog with gallbladder disease
http://lib.bioinfo.pl/pmid:17123257 along with other bacteria.
You can find all kinds of things in stool including parasite eggs for species dogs don't get infected with. Just because it is there doesn't mean its a health hazard. I fyour dog has access to rodent feces that might be all it is from.
If your vet indicated it is a health hazard for your dog you might ask for cases or information showing what those risks are.
I have not seen anything that indicates their is but of course you can ask your vet why they reported this to you and if they have any incidences of it being an issue.
You might keep her away from all rodent droppings and see if the next sample is different.
You might try a dose of fenbendazole (panacur or safe-guard which is over the counter) to ensure the intestinal tract is clear of parasites before breeding.
You can expect parasites anyway as the hormonal changes of pregnancy releases encysted larva from muscle tissue to reinfect mother dogs and pups.