Reduced post-natal versus pre-natal incidence of bent long bones and scapulae in a preliminary investigation using the Han Wistar rat.

There is a "chondrodystrophy" syndrome in the Han Wistar rat fetus that manifests as characteristic skeletal abnormalities such as bent and/or short long bones, and is classified as permanent detrimental abnormalities (major malformations). This pilot study investigated whether these defects resolve after birth. Han Wistar rats were dosed during organogenesis either with vehicle or test article. Examination of gestation day 20 fetuses showed a slightly increased incidence (11%; 11/101) of skeletal abnormalities in the high dose fetuses compared with 6% (4/67) in control fetuses, whereas no skeletal abnormalities were present in the 205 pups examined on post-natal day 21. The probability of having zero litters containing pups with skeletal abnormalities was p<0.0000001. This very low probability suggests that these defects recover by weaning and supports the hypothesis that these fetal findings in the Han Wistar are probably not permanent abnormalities and therefore are potentially reclassifiable as minor malformations.