[Fertility of male Syrian hamsters paired with one, two and four proestrous females each].

In order to improve the productivity of Syrian hamsters, we investigated whether a male could impregnate overnight more than one proestrous female. Twenty-one males and 49 females aged 8 to 10 weeks were used in this experiment. The mating systems were as follows: one male was paired with one female, one male was paired with two females, and one male was paired with four females. Six out of 7, 7 of 14 and 4 of 28 females became pregnant and gave birth under these three systems, respectively. We conclude that it is possible for a male to impregnate overnight about one female under the above mating systems.