Effect of constant light on parturition and postpartum reproduction in the rat

Light-dark (LD) cyclicity contributes to a number of reproductive events in the rat, including estrus cyclicity, and the timing of parturition and postpartum estrus. Constant light (LL) disrupts the female's cyclicity, and fertility is typically diminished. To ascertain whether constant light similarly diminishes the fertility of postpartum females, LL and LD animals were compared over three successive pregnancies on several reproductive measures including parturition, postpartum estrus and spontaneous ovulation, the timing of estrus relative to parturition, and the number, body weights, and viability of offspring. While the 24 h pattern of parturition differed for LL and LD groups, postpartum estrus and ovulation occurred reliably in both groups. The LD group showed greater variation in the birth-estrus interval, the result of a delayed estrus in those females giving birth late in the light phase. The likelihood of spontaneous ovulation and overall successful reproduction was high for both groups. Thus, unlike the cycling female, the fertility of the postpartum female is relatively unaffected by constant light. As such, these findings suggest that LD cyclicity is not critical for postpartum ovulation and estrus.