シロネズミの出産回数ならびに出産年令からみた産児数の変動

概要

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The present paper deals with some numerical observations involving the effect of maternal age on the litter-size in nine strains of laboratory rats which have been maintained since 1952. The numerical data were derived from a total of 1673 litters containing 11105 individuals obtained during a period from 1957 to 1962. The results are outlined as follows : 1) The litter-size of all rats tended generally to increase in the second litter. The first and third litters were relatively small, and the litter-size decreased with an increase of litter series. The Wistar strain, Wistar-King-A strain, Tokyo strain, Gifu strain, Gifu-agouti strain and Wayne's pink-eyed-hooded strain all showed this tendency in variation of litter-size in relation to litter series (Fig. 1). The Fischer-344 strain, Buffalo strain and Long-Evans strain, however, showed a characteristic variation of their litter-sizes (Fig. 2). 2) The litter-size of all strains showed a general tendency to increase up to 125 days of the mother's age (Table 4). No strain showed a specific variation of litter-size according to the mother's age. 3) High mortality of new borns was found in litters derived from both young and old mothers. But there was no remarkable mortality variation specific to any strain (Tabel 5).
1963-03-15