Differences in spontaneous fetal abnormalities among three outbred stocks of Wistar Hannover rats in Japan.

Wistar Hannover rats, which are maintained by three animal breeders in Japan, were examined to obtain basic data on reproductive and developmental parameters. Untreated pregnant females were terminated on gestational day 20, and the fetuses were removed by cesarian section. The fetuses were counted, weighed and examined for morphological abnormalities. There were few differences among the three stocks of Wistar Hannover rats on the numbers of implantations and live fetuses, sex ratio and fetal weights. The most common fetal abnormalities were the presence of left-sided umbilical arteries, supernumerary ribs and wavy ribs. The incidences of these abnormalities were different among the three stocks of Wistar Hannover rats. Our results provide important data which should be considered in the determination of which stock of rat is used in developmental studies.