Effect of Altered Photoperiod on Estrous Cycle, Pregnancy and Onset of Puberty in the Rat1

Effect of altered short-day photoperiod 2L:2D (SDP) on the length of estrous cycle, conception rate, duration of pregnancy, and age of sexual maturity of the rat were determined. Most female rats exposed to SDP had prolonged or irregular estrous cycles (most with prolonged cornified smears), resulting in a reduced conception rate over a long time. Also SDP significantly prolonged pregnancy (by 0.8 to 1 day) and advanced the age of puberty (by 3 to 4 days). Although total amount of light equaled that in the control (12L:12D) day, the SDP adversely affected the rat's reproductive function. The results suggest that the changes in reproductive function which is ascribed to changes in the proportion of light per day may be equally effected by changes in periodicity of the lighting.