The effect of pregnancy and stress on the onset of placentophagia in Long-Evans rats

Most virgin rats do not eat placenta when it is presented to them; virtually all parturient rats do. This study was designed to examine the role of the duration and termination of pregnancy on the induction of placentophagia. Time-bred rats determined by a pretest not to be attracted to placenta (nonplacentophages), were tested for placentophagia on one of a number of days of pregnancy. A comparable group was tested for placentophagia after surgical termination of pregnancy on Day 21. Groups of virgins were run controlling for the time interval between the pretest and the placentophagia test, and for a time interval that included a “stressful” event. The results were that (a) the incidence of placentophagia rose gradually from Day 7 to Day 15 of pregnancy, then remained stable, at about 0.4, until delivery; (b) pregnancy termination did not produce an effect on placentophagia greater than that of unterminated pregnancy; (c) a pretest-test interval containing a “stressful” event produced significantly more placentophagia than one that did not contain such an event; and (d) the maximum level of placentophagia observed during pregnancy was the same as that produced in virgins by a “stressful” event.