-This study's aim is to investigate the relationship between stage and degree of restricted feeding during the gestation period and occurrence of abortion, premature birth or fetal damage in rabbits. The study was composed of 5 groups of pregnant Kbl:NZW rabbits that consisted of 8 animals each. These groups were subjected to restricted feeding in the following ways: (A) control group, free access to food, (B) 60 g per day from gestational days (GD) 6 to 18 (middle period), (C) 20 g per day from GD 6 to 18, (D) 20 g per day from GD 19 to 28 (post-middle period), and (E) 20 g per day from GD 6 to 28 (middle and post-middle periods). Even though all dams in Groups A, B and C went to full term, abortion or premature birth occurred to 2/8 and 8/8 dams in Groups D and E, respectively. Fetal lethality increased in Group C, which was subjected to restricted feeding at 20 g/head/day in the middle period. Slight inhibition of fetal growth was recorded only in Group D, which was subjected to restricted feeding in the postmiddle period. Restricted feeding at 20 g/head/day in the middle period induced no abortion or premature birth, but increased fetal lethality that in the middle and post-middle periods resulted in abortion or premature birth of all dams, and that in the post-middle period resulted in abortion or premature birth at low incidence and slightly inhibited fetal growth. These results demonstrated that the post-middle period is vulnerable to effects of reduced food consumption in pregnant rabbits.

Ethyl tertiary-butyl ether (ETBE) is commonly used as an oxygenated gasoline additive. In this study, the prenatal developmental toxicity of ETBE was determined in rabbits. New Zealand white rabbits were given ETBE by gavage at 100, 300, or 1,000 mg/kg/day on gestational days (GDs) 6-27, and the pregnancy outcome was determined on GD 28. Neither death nor abortion occurred in the pregnant rabbits at any dose. Slightly and significantly suppressed maternal body-weight gain and transiently decreased maternal food consumption were found at 1,000 mg/kg/day during the administration period. At this dose, no changes in clinical or macroscopic finding were noted in dams. No treatment-related changes were observed in any dam treated at 300 mg/kg/day or less. There was no significant effect of ETBE on the numbers of corpora lutea, implantations, live fetuses, resorptions and dead fetuses, incidences of pre- and postimplantation loss, viability of fetuses, fetal body weight, sex ratio of fetuses, or weights of gravid uteri. No significant difference was detected in the incidences of fetuses with malformations or variations between the ETBE-treated and control groups. Also, no adverse effects on the progress of ossification were noted in fetuses of dams given ETBE. Based on these findings, it is concluded that the no observed adverse effect levels of ETBE were 300 mg/kg/day for dams and 1,000 mg/kg/day for fetuses in rabbits.

Prenatal development of Kbl:Dutch rabbits was studied in comparison with Kbl:New Zealand white rabbits. Significantly accelerated ossification of the 5th and 6th sternebrae and a low incidence of fetuses with a 13th rib were characteristic features in the prenatal development of Kbl:Dutch rabbits in comparison with Kbl:New Zealand white rabbits. These characteristics were largely consistent with earlier studies of Dutch rabbits from different suppliers and are notable when Kbl:Dutch rabbits are used for the evaluation of skeletal ossification.

-The present study was undertaken to elucidate restraint effects of protecting jackets that are used to protect against biting the sites of percutaneous application in pregnant rabbits. Animals wore protecting jackets from gestational Day (GD) 0 to 19 (GD 0 group) or from GD 6 to 19 (GD 6 group). Major restraint effects were decreases in body weight gain and food consumption, which were marked during the first 2 to 13 days in jackets, and diminished thereafter. Therefore, the animals in the GD 0 group had almost recovered from the effects on GD 16, but those in the GD 6 group were still under the effects of restraint on GD 19. The above findings indicate that early start of habituation to protection jackets will provide better results in practical reproduction studies using percutaneous application in rabbits.