Q: "When at [a ferret show] I saw some male ferrets that had not been
neutered...they had really large [scrotums].  Is this normal?  Do they
all have such large [testes] and where do they go when they are no
longer in season?"
 
A: They head south to play ball in Mexico.
 
The following answer contains graphic descriptions of ferret sex and is
not recommended for young children, members of S&M Anonymous, or fans of
Ann Coulter.  Rush Limbaugh and Bill O'Reilly declined comment, but are
reported to have giggled and asked for a phone and privacy.
 
There is a general rule among mammals that in promiscuous species,
males have larger testes than males that are of the same body mass that
are from monogamous species.  A hypothesis to explain this general
observation suggests, in part, that if the goal is to insure successful
breeding, then promiscuous males need more ammunition for their cannon.
This is why the hypothesis is sometimes called "Sperm Wars."  Among other
things, it suggests that he who deposits the most sperm has the highest
chance of making babies in the reproduction lottery.  Assuming most
mammals have similar sperm production rates (not a great assumption), an
easy way to make more sperm is to increase the size of the little sperm
factories.  It's true; size matters if your goal is to make more
spermatozoa than your competitor.
 
Polecats, the progenitor of our domesticated ferrets, have a kind of
promiscuous reproductive strategy in which a jill could theoretically
mate with all hobs that overlap her territory.  Certainly, a polecat hob
could mate with several jills in a single reproductive season.  However,
in a practical sense, most polecat jills probably only successfully mate
with a single male per reproductive event.  The reason is because a
polecat hob captures the jill in heat, overpowers and pins her down,
drags her around, chews her neck until it is bloody, and has prolonged
sexual congress that is designed to cause ovulation and fertilization.
Only after the male is satisfied that the jill has ovulated -- presumably
by scent if some studies are correct -- will he willingly let her escape
from his powerful canines and hooked baculla.  Generally, this brings
the female out of heat, although the process is not instantaneous.  It
is possible the jill could mate with another male, get wrestled to the
ground, neck chewed, and mounted for another indeterminable time, and
ovulate again.  This has been widely reported anecdotally in the ferret
literature, but the possibility of occurrence in polecats is poorly
studied.
 
So, what about the size of a hob's testes; are they larger than to be
expected?  Probably not.  Although polecats are promiscuous by nature,
other aspects of their reproductive strategy (the sex until ovulation
thing) generally overpower the need to grow big 'uns.  To answer this
question, I consulted "Mammalian Body Masses," "Asdell's Patterns of
Mammalian Reproduction," and about two-dozen body composition papers.
The size of ferret testes is just about what should be expected for
their body size.
 
I suspect the startling observation of a pair of dangling fur-de-spheres
is unusual enough to spur this question.  Normally, males carry those
cute little baby makers hidden away until needed, just before they go
into rut.  Then they drop down to swing gently in the breeze, which isn't
a joke.  For the best sperm production, the testicles need to be about
2-9 degrees Centigrade cooler than core body temperatures.  Not only is
sperm produced better at cooler temperatures, but the numbers of mutated
or malformed sperm are reduced.  The swinging in the breeze isn't the
only way those reproductive nuggets keep from overheating; they also use
a countercurrent-heat-exchange mechanism, where the cooled venous blood
from the testes chills the warm arterial blood from the abdomen.  Now
you know what is meant by "chill out."
 
There is an aspect of this phenomenon that has direct bearing on current
ferret breeding.  For most of 2500 years, ferrets have been housed
outdoors.  Only in the last 30 years or so have ferrets been brought
inside the house.  Recently, I've been asked to investigate the strange
phenomenon that ferret reproductive success -- at a national level
with hobby breeders -- has suffered the last few years.  Litters are
reportedly smaller, more birth defects are noted, and an increase in
false pregnancies is being seen.
 
END OF PART 1, PART 2 TO FOLLOW
 
PART 2
 
I've come up with a few hypotheses about these problems:
 
1.  Deteriorated plastics (water bottles, plastic food storage containers
and bags, food dishes, cage wire coatings, etc.) may be producing enough
pseudohormones to cause problems.  These pseudohormones have been
strongly linked to birth defects and resorbed embryos in numerous
species.  Pseudohormones are not really hormones.  They are just
molecular fragments that -- by coincidence -- contain a binding site
that attaches to a hormone receptor site.  This prevents the real hormone
from attaching and regulating proper development.
 
2.  Phytochemicals, including phytoestrogens and other endocrine
disrupters (ED).  These are natural chemicals that are produced by
plants that could wind up in ferret kibbles.  There are two main types
of phytoestrogens of importance to ferrets.  The first is Lignans, found
in minor amounts in plant cell walls, and in high concentrations in oil
seeds, such as flaxseed.  They are also found in whole grains, cereal
brans, legumes and other vegetables.  The other phytoestrogens of
importance to ferrets are the Isoflavonoids.  These are found in a lot
of plants, but are particularly common in soy products.  Grains used to
construct kibble may contain enough trace amounts of endocrine disrupters
to impact reproductive success from either the male or female side.
 
3.  Diet may partially to blame.  It could be that some unknown trace
element is acting like a limiting factor.  It is also possible that the
chicken meal used in some kibbles contains trace amounts of residual
hormones (not plant based -- see above) that can impact the outcomes of
pregnancy.
 
4.  Both jills and hobs, being housed indoors, are being kept too warm,
and because they are caged, they cannot use natural behaviors to better
thermoregulate themselves, such as going underground, sprawling on a cool
floor, splashing in water, etc.  When jills are too warm during specific
periods of time during embryonic development, it can throw off the
development of the young.  Many of the resulting changes can mimic other
genetic problems, including neural crest disorders, cleft palates, and
far worse.  In males, the extra heat can reduce sperm quality and
quantity.  Ferrets are very sensitive to overheating, and while the
degree of hyperthermia is not enough to harm adult ferrets, it could be
enough to screw with reproduction.
 
5.  Breeding practices have introduced too many random or mutative errors
into some ferret lines, which are depressing reproductive success.  This
is a problem in many species, but currently no evidence exists that
suggests it is one with the majority of ferret breeders.  If the problem
is as widespread as some have suggested, it is probably not genetics, but
something in the environment.
 
Personally, I think the problem is multifactorial, but I am leaning to a
combination of overheating, and exposure to deteriorated plastics and
phytochemicals.  There may be other factors I have yet to consider (I'm
still studying the problem).  A great deal of applicable work has been
done on mink and fox by the fur industry.  The mink investigations in
particular hold great promise for understanding what is going on.
 
I am currently in the process of testing some of these hypotheses.  For
those of you that know Scarlett from Ohio, she has donated two whole
jills from her fine stock.  I have housed them in a cool (68 degrees),
natural light, plastics-free environment (only metal and wood), and have
only fed them mice and naturally grown chicken for most of the last year.
When they come into season in the spring, Scarlett has agreed to breed
them to healthy hobs and we will see if the different environment and
diet has an impact on litter size and success.  Yes, a tested population
of 2 is very small, so don't consider it a test, but rather a preliminary
result.  If it works out, the results can be retested with a larger
population that would have statistical significance.
 
The tests don't end there.  The kits will be randomly divided into two
groups.  One group will only be given an evolutionary diet and the other
group will eat commercially available kibbles.  Among other things, I
will make periodic evaluations of their activity cycles, growth rates and
adult size, kibble damage to teeth, weight, and health problems.  This
population can be small.  With the statistical data I already possess,
this test is simply to show the damage is not due to genetic problems,
but biomechanical forces.  Not that I really need the additional data.
The populations I have now are large enough, composed of so many
different ferrets from so many different areas, that the genetic question
has been resolved.  This is just to dispel the last tiny doubt.
 
The last part of this post has drifted away from the testicle question
a bit, but it relates if you realize the courage Scarlett displays in
assisting my efforts to, um, ferret out some understanding to current
problems in ferret reproduction.  Need I say it?  The lady has hurones
cahones.
 
Bob C   [log in to unmask]
[Posted in FML issue 5341]