The breeding and use of specific pathogen-free (SPF) rats.

Bronchiectasis is common in older rats and is a serious complication when the lungs are repuired for research purposes. SPF rats do not develop this complication, but special isolated accommodation must be provided and care of the animals must avoid introduction of outside micro-organisms. Animals removed from the isolated accommodation for experimental work are not returned, but can be kept in the general animal house provided there are no conventionally-bred rats.