The methodology described is for mice and would be adjusted to synchronize with the rat reproductive cycle:
This short-term test for reproductive and developmental toxicity provide preliminary data on the toxicity of chemicals about which little or no data exist. Test animals are mated for 3 days prior to chemical exposure to produce time-mated females for gestational exposure and to ascertain fertility of the untreated males. The group of time-mated females are treated during Gestation Days 8-14 and allowed to litter for observations through Postnatal Day (PND) 4. Endpoints observed include pup number and body weights on PND 0, 1, and 4 and number of uterine implantation sites on PND 4. A second group of females is dosed daily for 19 days. After 7 days, these females (n = 10/group) are cohabited with males who had been treated for 5 days prior to this second mating. Daily chemical dosing continues during the 5-day cohabitation. This second group of females is killed after 19 days of treatment and the number of live and dead fetuses and implantation sites are recorded. After 17 days of dosing, males are killed and the reproductive system evaluated by organ weights, total epididymal sperm counts and motility, and testicular histology. This design can be used to prioritize chemicals for further study, or to delineate the relative toxicities of structurally related chemicals, and to identify the proper dose range for subsequent toxicity studies.
Harris, M.W., Chapin, R.E., Lockhart, A.C., and Jokinen, M.P. (1992) Assessment of short-term reproductive and developmental toxicity screen. Fundam. Appl. Toxicol. 19:186-196.