Placentophagia in Nonpregnant Nulliparous Mice: A Genetic Investigation1

GENETICS OF PLACENTOPHAGIA

distribution patterns were cataloged. Testing of the appropriate congenic line
in the experimental situation would verify the locus of the gene in question if
the congenic line behaves Uke animals of the substituted genotype rather than Uke
animals of the background genotype (Klein, 1973). Although the Ri-strain tech-
nique is relatively new, several studies employing this particular Ri-strain
battery already exist in the literature (e.g., Eleftheriou and Bailey, 1972;
Oliverio, Eleftheriou, and Bailey, 1973; Eleftheriou and Kristal, 1974).

All females were tested at 60-70 days of age. Each female was presented
with one to three placentas, removed surgically from either a BALB∕cBy or a
C57BL∕6By donor on the last full day of pregnancy. After removal from the
donor, the placentas were frozen with a few drops of normal saline, and
thawed immediately prior to testing. Body-temperature placentas were pre-
sented in small, Untippable glass dishes for 15 min to females in individual,
clean, plastic cages. All mice were housed on a 7:00 AM to 7:00 PM daylight
cycle. Two hours prior to testing, food was removed from the cages of the
test mice, and the cages were placed in the testing room. Fifteen minutes
prior to testing, each female was placed in her test cage. The behavior of each
female toward placenta was observed during the 15-min test. The presence or
absence of placentophagia was scored; unless the placenta was picked up and
some part of it was actually eaten, a negative score was given. The test was
easy to score in that the behaviors of the eaters and noneaters were clearly
different.

The results of the exposure of virgin females of the RI-strain battery to
placenta are presented in Table 1.

TABLE 1

Incidence of Placentophagia in Nonpregnant NulIiparous Female Mice

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