Many of the studies conducted to examine the developmental and reproductive 
toxicity potential of candidate pharmaceuticals use the Sprague-Dawley rat as 
the animal model. This is due in part to the large database for this outbred rat 
available for comparison of litter data, and the low incidence of fetal 
malformations and variations. The following study was conducted to generate 
information on potential embryo-fetal developmental defects and litter data in 
another outbred stock of rat, the Wistar Hannover. One hundred fifty pregnant 
female Wistar Hannover rats (Tac:Glx:WIfBR) were dosed orally once per day with 
distilled water from Gestation Days (GD) 6 through 17 covering the time from 
implantation to closure of the hard palate (GD0 = day of insemination). 
Caesarean sections were performed on Day 20 of gestation. All fetuses were 
examined for external, visceral and skeletal malformations and variations. 
Macroscopic and histomorphologic examinations were also completed for the F0 
females at termination. The percent pregnant (88%) and litter size (average 
10.6) were found to be lower than that commonly reported for the Sprague-Dawley 
rat (Crl:CD (SD)BR; 95.4% and 14.6, respectively). Pre-implantation loss 
(14.1%), post-implantation loss (7.4%) and percent resorptions (7.2%) occurred 
at a higher incidence than typically seen in the Sprague-Dawley rat (5.9, 5.6 
and 5.1%, respectively). The average fetal body weights for both the female and 
male rats were lower than those typically seen in the Sprague-Dawley rat. 
External, visceral and skeletal examination of the F1 fetuses revealed numerous 
malformations and variations which also occurred at higher incidences than those 
reported for the Sprague-Dawley rat. Routine macroscopic and histomorphologic 
examination showed there were no changes that would be interpreted to have 
impaired mating performance, fertility or gestation. Thus, this study provides 
information on the reproductive effects and the background incidence of 
embryo-fetal development defects that could be used for comparison to those 
identified when using this outbred rat for developmental and reproductive 
toxicity studies, as well as for comparison to the more commonly used rat stock, 
the Sprague-Dawley rat. For the parameters evaluated, the Wistar Hannover rat 
had greater variability and an increased incidence of spontaneous malformations 
as compared to the Crl:CD (SD)BR Sprague-Dawley rat. These findings should be 
considered if this stock of rat is selected in the conduct of developmental and 
reproductive toxicity studies.