In order to efficiently generate genetically engineered mouse (GEM) fetuses or neonates of a specified age range, researchers must develop strain-specific strategies, including reliable early pregnancy detection. The authors evaluated pregnancy indices (pregnancy rate, plug rate, pregnant plugged rate, first litter size and body weight) in two GEM breeding colonies: homozygous soluble epoxide hydrolase knockout (sEHKO) mice (n = 164 females) and L7-tau-green fluorescent protein (GFP) transgenic mice (n = 61 females). The goals of the study were to determine the most accurate early pregnancy indicator and to reliably and cost-effectively produce timed pregnant females that were between gestation days 16 and 18. The authors set up each timed mating by placing two naturally synchronized females with a male for 48 h. When males were present, personnel checked each female daily for a vaginal plug. They then weighed the females immediately, 1 week and 2 weeks after removing the males. In both sEHKO and GFP colonies, increases in body weight at 1 and 2 weeks after timed male exposure more reliably and consistently indicated pregnancy than did plug detection. Further evaluations and protocol refinements are planned based on litter size and litter number in these colonies.
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This study was supported by grants NS49210, NS20020 and NS044313 from the National Institutes of Health. We thank Dr. Debra L. Hickman for her review and comments on preliminary versions of this manuscript; Nabil Alkayed, MD, PhD and Paco Herson, PhD for their support of this study by providing the sEHKO and GFP mouse colonies, respectively; Sarah Shangraw for assistance with the husbandry manipulations and body weight measurements of the animals used in this study; Jennifer Young, Patty Ayala and Melissa Hernandez for collecting data regarding litter size; John Todd and Ashley Branch for assistance with manuscript figures; and Charles River Laboratories and The Jackson Laboratory for providing information on pregnancy indices in C57BL/6NCrl and C57BL/6J mice, respectively.