Toshiaki Hino1, Kanako Oda1, Kenji Nakamura1, Yutaka Toyoda2, Minesuke Yokoyama1,3. 1. Mitsubishi Kagaku Institute of Life Sciences (MITILS) Tokyo Japan. 2. National Research Center for Protozoan Diseases Obihiro University of Agriculture and Veterinary Medicine Hokkaido Japan. 3. Brain Research Institute Niigata University 1-757 Asahimachi dori 951-8585 Niigata Japan.
Abstract
PURPOSE: 129 inbred mice show poor reproductive ability, as evidenced by small litters; however, the exact cause of this is unknown. In the present in vivo study we examined fertility and subsequent post-implantation development in an attempt to clarify the cause of small litter size in 129 mice. METHODS: 129 or C57BL/6J females that displayed vaginal plugs 1 day after mating with males of the same strain were examined for the presence of fertilized eggs. Reciprocal matings were also performed between 129 and C57BL/6J mice. Subsequent post-implantation development of fertilized eggs was examined by dissecting females 18-19 days after the vaginal plugs were found. RESULTS: Mean numbers of recovered eggs were 7.9 and 8.0 in 129 and C57BL/6J mice, respectively. Half of the recovered eggs were unfertilized in 129 mice, whereas all were fertilized in C57BL/6J mice. Mean numbers of live fetuses 18-19 days after mating were significantly lower in 129 mice (4.7) than in C57BL/6J mice (7.3). In different types of pairings using both strains of mice, the fertility was significantly lower whenever 129 females were used. CONCLUSIONS: The small litter size in 129 mice is caused by low fertility resulting from female factors.
PURPOSE: 129 inbred mice show poor reproductive ability, as evidenced by small litters; however, the exact cause of this is unknown. In the present in vivo study we examined fertility and subsequent post-implantation development in an attempt to clarify the cause of small litter size in 129 mice. METHODS: 129 or C57BL/6J females that displayed vaginal plugs 1 day after mating with males of the same strain were examined for the presence of fertilized eggs. Reciprocal matings were also performed between 129 and C57BL/6J mice. Subsequent post-implantation development of fertilized eggs was examined by dissecting females 18-19 days after the vaginal plugs were found. RESULTS: Mean numbers of recovered eggs were 7.9 and 8.0 in 129 and C57BL/6J mice, respectively. Half of the recovered eggs were unfertilized in 129 mice, whereas all were fertilized in C57BL/6J mice. Mean numbers of live fetuses 18-19 days after mating were significantly lower in 129 mice (4.7) than in C57BL/6J mice (7.3). In different types of pairings using both strains of mice, the fertility was significantly lower whenever 129 females were used. CONCLUSIONS: The small litter size in 129 mice is caused by low fertility resulting from female factors.
Entities:
Keywords:
129 mice; Female factors; Fertility in vivo; Poor reproduction; Small litter size