The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
"Reproductive Assessment by Continuous Breeding" (RACB) protocol was originally designed using mice as the test species. The purpose of the present study was to develop a RACB protocol in CD Sprague-Dawley rats. Ethylene glycol monomethyl ether (EGMME), a known reproductive toxicant, was used as the test article. Dose levels selected were 0.01, 0.03, and 0.10%, administered via drinking water. In a modification of the standard protocol, male and female rats ~20 pairs per treatment group, 40 pairs of control animals) were cohabited for approximately 6 weeks, separated to allow delivery, nursing and weaning of the second litter, then re- cohabited for approximately nine more weeks. The weaned second litter was used for F1 reproductive testing. The control and 0.03% F0 pairs were also utilized for a crossover mating trial to determine the affected sex.
Only one litter was born in the 0.10% dose group, and no pups were available for F1 testing. At 0.03% level of EGMME, number of live pups per litter and proportion of pups born alive decreased significantly, both in F0 and F1 testing. In the crossover mating, proportion of pups born alive decreased significantly in the 0.03% male X control female group. Declining control F0 fertility and productivity noted in this study indicate that the standard RACB design (weaning last rather than second litter) is better suited to use with rats.