Undergraduate Research Journal

Effects of Dietary Phytoestrogens on Paternal Responsiveness and Maturation in the Biparental California Mouse
Aaron T. Stamp, Trey Amador
studies; however, the method by which Nelson et. al (27)
quantified sperm counts was not described.
We considered the possibility that the differences in soy
content between the diets used in our study were too small
to affect our measures. This seems unlikely, as Wisniewski
et al. (28) studied the effect of a high-Genistein diet
of 300 ppm (almost 3 times as low as our HS diet) on
C57BL/6 mice and found a significant decrease in testis
size compared to mice not exposed to Genistein, with mice
being of approximately equal age as those in our study
(28). Another possibility is that the testes and fat pads are
not as responsive to estrogens in California mice as in
some other species; however, no data are available with
which to evaluate this hypothesis.
Analysis of body mass over time revealed that the LS
group was initially heavier than the HS and MS groups but
gained body mass more slowly over the next few months
than the HS mice. This result is consistent with previous
findings in which male C57BL/6 mice that were exposed to
dietary Genistein weighed less than controls at the age of
puberty (40-45 days of age) (28). Importantly, though, the
only time point at which body mass differed significantly
among our groups was at weaning and from week 1
through week 3 after weaning; at the time of sacrifice,
no significant differences were observed. Therefore, it is
unclear whether the increased body-mass gain in the HS
group resulted from their diet or was simply an artifact of
their lower body mass at the time of weaning.
CONCLUSION AND FUTURE OBJECTIVES
This is one of the first studies to determine if soy has an
effect on parental behavior in any species. The results may
be of interest to animal researchers, zoo administrators,
and farmers, as soy is common in many animal feeds and
bedding. This study also has implications for the human
population, as soy consumption has been increasing
steadily in the United States since the 1950’s (29). In the
near future, we hope to assay the blood samples from our
animals for plasma testosterone and Daidzein or Genistein
concentrations, and to quantify ER-α expression in the
collected brains, to further characterize possible effects of
dietary phytoestrogens in male California mice. Eventually,
a similar study examining organizational effects could
be employed.
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