OBSERVATION OF PLACENTOPHAGIA
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Baseline effect. Two days after the fourth placenta exposure,
20 subjects were placed in observation compartments. Each pair
of subjects flanked a normal, nonpregnant, non-food-deprived
Long-Evans multipara. The stimulus rat had water available but
not food. The trio remained in their compartments for 6.5 h
(median duration of parturition, as determined in our laboratory).
Ninety minutes before the end of the session, a placenta was put
into the feeder of each subject’s compartment. The feeder in one
compartment had a perforated Plexiglas lid, enabling the subject
to see and smell the placenta but not eat it (no-access group). The
feeder in the other compartment had no lid, enabling the subject
to eat the placenta (access group). At the end of the 6.5-h period,
the rats were returned to their home cages and the test chambers
were thoroughly cleaned.
The next day, each subject was given a standard placento-
phagia test. Since only the access-group rats could have eaten
placenta in the observation compartment, the only criterion for
Placentophagia was eating placenta on the test that occurred the
following day. In this way, the proportion of nonplacentophages
that became placentophages, and the proportion that ate during
the observation period but did not eat on the placentophagia test
the next day, could be determined.
Observing parturient, placentophagic, and chow-eating stimulus
rats. Observation sessions were conducted on the day after the
fourth placenta exposure. One subject was assigned randomly to
each of the six conditions: (1) observing parturition and having
access to placenta (part∕access group); (2) observing parturition
but not having access to placenta (part∕no-access group); (3) ob-
serving placentophagia and having access to placenta (plac∕access
group); (4) observing placentophagia but not having access to pla-
centa (plac∕no-access group); (5) observing eating of chow and
having access to placenta (chow/access group); and (6) observing
eating of chow but not having access to placenta (chow∕no-access
group).
The access and no-access subjects were treated identically to
corresponding subjects in the baseline situation, except for the
determination of the duration of placenta exposure. In this phase
of the study, all three stimulus conditions were run simultane-
ously. When the pregnant stimulus rat was in the afternoon of
Day 22 of pregnancy, she was placed in the center compartment
of one of the three chambers, and the other two stimulus rats and
six subjects were placed in theirs. The pregnant stimulus rat and
the six subjects were each given five pellets of chow. Twenty min-
utes after delivery of the first pup by the pregnant stimulus rat,
we presented a donor placenta to each of the subjects and 18
donor placentas to the placentophagic stimulus rat. The stimulus
rats that would be observed eating chow had not been given food
when moved to the observation compartment. They had, there-
fore, been food-deprived for 12-30 h. Twenty minutes after the
beginning of delivery, when the placentophagic stimulus rat was
given 18 placentas, the chow eater was given three full-size pellets
of laboratory chow. At the completion of delivery, the subjects
and stimulus rats were returned to their home cages.
The next day, all six of the subjects in that battery were given
a standard placentophagia test (Test 1), as described above.
To control for the amount of exposure to pups received by the
subjects observing parturition, after Test 1 all subjects were re-
turned to the same compartments they had occupied the previous
day. This time, the four subjects that had observed rats without
rat pups the previous day were exposed to a litter of I- to 2-day-
old rat pups, which was the same size as the litter delivered the
day before. The litter (without an adult) was placed in the central
compartment; duration of exposure to the litter was matched to
the duration of parturition the previous day. The two subjects
that had originally observed parturition were exposed to an empty
central compartment during this phase of the experiment. After
the exposure period, all subjects were returned to their home cages.
One day later, each subject was moved to a 10-gal aquarium
containing 3 cm of coarse sawdust, a food hopper, and a water
bottle. She was allowed to habituate to the cage for 24 h, after
which she was given constant exposure to four 3- to 8-day-old
foster pups, in a standard concaveation procedure (Wiesner &
Sheard, 1933). Pups were replaced at about 0900 h. Each time
new pups were placed around the cage, the rat was observed for
15 min to determine whether she was maternal toward them. A
second 15-min observation was conducted at about 2100 h. Cri-
terion for maternal behavior was the presence of all of the follow-
ing during the 15-min test: (1) retrieval of all four pups to a central
site; (2) licking of the pups, particularly in the anogenital region;
and (3) crouching over the pups (Rosenblatt, 1967). This con-
caveation procedure was continued for 8 days, whether or not
the subject became maternal.
On the day after the last day of pup-exposure, each subject
was given another standard placentophagia test (Test 2), which
WasconductedidenticallytoTest 1.
This overall procedure was repeated 15 times, until each of the
six groups contained 15 subjects.
RESULTS
Baseline
The proportions of placentophages found during
the baseline assessment and during Tests 1 and 2 are
presented in Table 1. Of the 10 rats in the baseline
group that had had access to placenta during the ob-
servation session, three ate placenta the next day.
Those three, and four others, had eaten the proffered
placenta during the observation session, but only
those three ate placenta during the placentophagia
test.
None of the 10 rats in the baseline group that did
not have access to placenta during the observation
session ate during the placentophagia test on the next
day. The difference in the proportion of placento-
phages between the access group (.30) and the no-
access group (.00) was not significant (p = .1 ɪ, Fisher
exact probability test).
Test 1
In the access group, there were two more rats in
each observation condition that ate placenta during
the observation session than there were that ate in
Test 1. This is similar to the situation that occurred
among the baseline-group rats that had access to pla-
centa. Using the proportion that ate during observa-
tion in the baseline group to compute the expected
frequency of placentophages during the observation
session in Test 1 (expected frequency = 11), a chi-
square analysis was performed on the observed fre-
quencies (part∕access = 12, plac∕access= 10, chow/
access = ?). The observed frequencies were not sig-
nificantly different from the expected frequency
[χ2(2)= 1.63, p > .05].
The proportion of placentophages in the group ob-
serving stimulus rats eating chow that had access to
placenta (chow∕access) was not significantly differ-
ent from that of the baseline∕access group (5/15 vs.
3/10; p =.61, Fisher exact probability test). The
chow∕no-access group was not significantly different
from the baseline∕no-access group (1/15 vs. 0/10;