[Dating pregnancy times in rats and the effect of ovum supermaturation on the quantity of live embryos].

The fecundity of white rats was compared for the night and morning matings (late and early). The mating of animals at the stage of oestrus for 1.5 hrs early in the morning is the optimum one for obtaining females with the precisely dated time of pregnancy. The progeny of females fertilized after 10-11 hours in the morning, i. e. 9-11 hrs after the ovulation, decreases almost twice at the expense of embryonic mortality both prior and after the implantation due to the low viability of "overmatured" eggs.