I am wishing Montana a not so Happy Anniversary. It is now 15 years since my colleagues and I brought to the attention of the Montana Department of Fish, Wildlife and Parks and then Governor Marc Racicot that the scrotal sac on white-tailed deer is being formed during development as a fetus with the left hemiscrota and left testis directly forward of the right hemiscrota and right testis. Our peer-reviewed study published in 2002 was first to report this condition, now the norm as over 70% of male fawns are being born this way each year. Only 30% or less of male fawns are born with bilateral
hemiscrota and testes as used to be the norm.
It took only 15 years for this drastic epigenetic change in anatomy to happen. Deer with bilateral hemiscrota will soon be considered abnormal, because misaligned hemiscrota are what most hunters see. This condition does not affect a male’s ability to reproduce as long as the hemiscrota are large enough to contain the testes away from the heat of the body wall.
This enables males with misaligned hemiscrota to pass this epigenetic change to their male offspring, likely the reason this condition has become the norm so quickly.
On affected male animals the testes descend with the left forward of the right because the left testicular lymph node is misplaced forward of the right testicular lymph node during development of the reproductive organs as a fetus. We do not know the prevalence of this condition in species other than white-tailed deer, although it appears to also be very high on bison in Yellowstone National Park and mule deer throughout Montana. It has also been documented on fox squirrels,
mice, hamster, domestic sheep, dogs, elk, antelope and bighorn sheep, including both live and dead animals.