Selection of food allotment for New Zealand white rabbits in developmental toxicity studies

In three initial studies, female rabbits were fed 125, 150, or 230 g of Purina Certified Rabbit Chow No. 5322 (“regular” chow) per day or 150 g/day of Purina Certified High Fiber Rabbit Chow (“high fiber” chow) for at least 5 weeks prior to artificial insemination and until Day 28 of gestation when fetuses were removed and examined. Animals allotted 230 g/day of regular chow ate approximately 180 g/day and gained more weight than the 150 g/day group until Day 14 of gestation after which food consumption declined and body weight decreased. Animals fed 150 g/day regular chow ate all food provided until after Day 22 of gestation when food consumption decreased dramatically in some animals. Animals in the 125 g/day regular chow and 150 g/day high fiber chow groups ate essentially all food provided throughout gestation. Ad lib feeding in the 230 g/day groups was associated with adverse reproductive consequences consisting of decreased numbers of implants and live fetuses and decreased fetal weight. In one study involving 3 groups fed 125 and 150 g/day regular chow and 150 g/day high fiber chow, reproductive parameters were similar in all 3 groups. However, fetal weight in the 150 g/day regular chow group was 50% more variable than the other groups in association with more variable maternal body weight change late in gestation in that group. In subsequent studies using 125 g/day, there has consistently been fewer animals going off feed late in gestation and a decrease in fetal weight variance of approximately 60% compared to previously when the standard daily allotment was 150 g/day. These results establish that a daily allotment of 125 g regular chow is sufficient and preferable to 150 g/day regular chow for animals which are to be terminated on Day 28 of gestation as in developmental toxicity studies. A diet of 150 g/day “high fiber” chow offered no advantage over 125 g/day regular chow which itself has an adequately high fiber content.