Further studies of post-partum ovulation timing in mice

The times at which post-partum ovulation occurred relative to the times of parturition, were similar for CD-1 mice exposed either to 18L:6D of 10L:14D and comparable to the times reported previously for mice of the same strain kept under 14L:10D. When parturition took place close to 'lights off', ovulation tended to occur 13--14 h after littering (i.e. during the last part of the same dark period and the early part of the next light period). Conversely, when parturition took place closer to 'lights on', ovulation tended to be delayed by the equivalent number of hours so that it occurred during the last part of the next dark period and early part of the subsequent light period. This confirmation and extension of earlier work suggests that mice of this strain would be useful for investigating hormonal events associated with the timing of post-partum ovulation in the mouse.