Abstract
The objective was to evaluate the influence of colony aging in a Swiss Webster (SW) outbred stock used as recipients for embryo transfer. In the first study, a retrospective analysis was performed throughout several generations during a 38-month period in 2,398 embryos transferred to 108 SW recipients. A decrease in the percentage of live pups from transferred embryos was found at the end of the period. Impairment occurred due to the incidence of maternal cannibalism that increased from 0% to 67-100% (P<0.05), while pregnancy rate (pregnant/transferred recipients) and number of pups per delivered female were not affected throughout the period (P=NS). A following study was carried out to compare the reproductive performance of SW stock vs. B6D2F1 hybrid females in a 5-year interval. The study was conducted on a total of 893 embryos transferred to 40 females (20 SW and 20 B6D2F1) in Year #1, and 514 embryos transferred to 30 females (15 SW and 15 B6D2F1) in Year #5. No cases of maternal cannibalism were found on Year #1 in any of the strains (0/10 and 0/10). However, an incidence of 44,4% (4/9) was seen on Year #5 for SW, while for B6D2F1 the incidence was 0% (0/12) (P<0.05). Further examination of the uterus showed endometrial cysts and abnormal implantation sites in SW on Year #5 but not in B6D2F1 females. In conclusion, this study reports an impairment of the reproductive performance of an early aged SW outbred stock colony mainly due to the occurrence of maternal cannibalism. This finding has important implications for embryo transfer programs conducted in mouse facilities.
Highlights
Embryo transfer (ET) is an indispensable tool used in mouse facilities, with several applications in biomedical research
While pregnancy rate and number of pups per delivered female were not affected in this period, a negative correlation was found at the end of the period in produced live pups from transferred embryos, which was due to a high incidence of maternal cannibalism
While the occurrence of cannibalism was not found on Year #1 in any recipient strain, it was detected in 44.4% of Swiss Webster (SW) females on Year #5
Summary
Embryo transfer (ET) is an indispensable tool used in mouse facilities, with several applications in biomedical research. ET is the first choice to perform embryo rederivation to clean mouse strains from pathogen agents before entering into a barrier housing facility (Sztein et al, 2011; Van Keuren and Saunders, 2004). For this purpose, embryos are thoroughly washed in specific media as recommended by the International Embryo Technology Society (Stringfellow et al, 2007) and transferred into a “clean” recipient female (Sztein et al, 2011). ET of cryopreserved embryos or gametes is a very useful tool to revitalize murine lines
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