シロネズミの出産数ならびに産児数の季節的変動

概要

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The present paper gives some numerical data concerning seasonal variations of the reproductive activity in nine strains of laboratory rats. The numerical data were derived from a total of 1673 litters containing 11105 new borns obtained during a period from 1957 to 19162. The results are outlined as follows: 1). Monthly variations of birth rate, litter-size and mortality of new borns are shown in Tables 1 to 4. There was no evident difference birth rate, litter-size and mortality of new borns according to strain. 2). Birth rate showed an increase in spring and summer in the Wistar strain, Long-Evans strain, Tokyo strain, Gifu-agouti strain, Wistar-King-A strain, and Fischer-344 strain, while the birth rate of the Gifu strain, Buffalo strain and Wayne's pink-eyed-hooded strain decreased in spring and summer (Table 5). 3). Litter-size showed generally a slight increase in spring, though there were slight seasonal variations according to strain (Table 5). 4). High mortality among new borns was found in autumn and winter in most strains. Only Wayne's pink-eyed-hooded strain showed a characteristic seasonal variation with a high mortality in the summer (Table 5). According to the results it appears that seasonal variations of reproductive activity seem to be caused by environmental factors.
1963-05-15