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Jay Russell, Ph.D. with his Coton de Tulear |
LGD - An Anatolian Shepherd |
If your Livestock Guardian Dog (LGD) is dark-coated,
then it will absorb heat from solar radiation quickly; if your LGD is
light-coated, it will absorb heat from solar radiation slowly. Eventually,
all things will attain an equillibrium, but it is the speed at which that
equillibrium state occurs that usually chills us mammals to the bone or
fries us like bacon. Color aside, your LGD's hair length and coat
condition are crucial factors determining its ability to tolerate the
daytime heat load. It is actually all biophysics (mostly Newton's Law of
Cooling) and it is not difficult to get a grasp of the concepts involved
(trust me on this).
Ta is the Temperature at the tip of the hair.
Ts is the Temperature at the surface of the skin.
L is the distance between the tip of the hair and the surface of
the skin.
NEWTON's FORMULA:
(Ta minus Ts) C = (F) x ------------- L
C is "conductance," the speed at which the Temperature
at the tip of the hair (Ta) will be equal to the Temperature at the skin's
surface (Ts).
F is a number, determined through experiment, which estimates the
ability of a hair to conduct heat. Dry oiless hair (like that of a Coton
de Tulear) has a very small number, while silky, oily hair has a very big
number. The bigger the number "F", then the faster the dog will gain or
lose heat at the surface of the skin. I'll ignore it here. NB: to my
knowledge, this number has never been determined for any dog.
Okay, now a few facts. Most mammals attempt to keep
their skin temperature at about 85 degrees F (29 deg C). The sun can heat
the tip of a hair to more than 150 degrees F (66 deg C). Plug in those
temps to the formula and you get (Ta - Ts) is (150 - 85) which is "65," a
big number. Now, divide that number by the length of the hair (for metric-philes,
just use cms).
If the hair is six inches long, then the the number
"C" shrinks to 10.8. The dog's skin will stay cool longer. If the dog
has been clipped to 1-inch, then conductance, C, will remain at 65
and the dog's skin will heat quickly. And, if you surgically clip Fido to
say 1/8th of an inch, then you'd divide 65 by 0.125 and get a conductance
value, C, of 520. The dog's skin temperature would equal the hair
tip's temperature in a twinkling of an eye (i.e., divide 520 by 65 and you
see that heat will transfer eight times faster than it would if you had
left the hair at 1-inch long).
Now just play with numbers. Want to see what would
happen if the dog's usual 6-inch coat was heavily matted? Just decrease
"L." What happens if it is nighttime and the ambient temperature drops to
40 degrees? Just substitute "40" for "Ta" ("C" will be negative number,
indicating that your pooch is loosing skin heat towards the tip of its
hair and the environment beyond). If a dog exercises, then its Ts will
increase as its body attempts to dump the heat load to the oustside. A dog
will pant when its Ts is high and the Ta is high and/or when its Ts is
high and "F" is low.
If a dog is really suffering, soaking it with water
quickly makes "F" a big number (water is much more conductive than cotton
or air or normal hair, for example) and simultaneously flattens the coat
making "L" a small number. A matted coat impedes the dogs own ability to
vary "L" (which it normally does by erecting or flattening its topcoat
hairs using the follicle's tiny "erector" muscles) and mats also alter the
"F" value, probably making "F" a smaller number. Matted dogs cannot dump
heat from their skin surface to the outside air, a potentially dangerous
situation.
Pretty nifty, no? With Newton's formula, you can get a
glimpse of what your dog might be feeling (no small accomplishment for us
thin-haired, sweaty-skinned primates who are obsessed with adulterating
hair, changing its reflectivity, varying its length, and otherwise messing
with Mom Nature).
BTW: bird fanciers can play with this formula and gain
insight into why a bird fluffs up its feathers or flattens them. Bird
feathers are known to have a really small value for "F" showing that
feathers (modified reptilain scales) are waaaaay better than typical
mammalian hair at slowing down thermal conduction. That's why you might
have a down jacket rather than one stuffed with Anatolian clippings.
There's no substitute for a big "L" and a little "F" when it comes to
outerwear. Oh yes, one last point. For those of you with a hairless breed,
the formula doesn't work because there is no "L" to consider. A Xolo or
Chinese Crested is at the whim of the sun and the air. A naked LGD would
be a pretty unhappy dude.
COAT COLOR, HAIR LENGTH, and COOLING
Above, I noted that long hair usually protects a mammal
from heat gain through solar radiation. And indeed, most LGDs, created to
stand outside and protect hoofed stock from predators, are either white,
fawn, or light-brown colored, hence solar energy absorbtion isn't high on
their list of concerns. But I just received an excellent series of email
questions and comments from a person whose black Standard Poodle is
estactic when clipped short in the summertime. Why? I thought I'd share
some of my response to her email with you....
Black is the PERFECT solar radiation energy
absorber, hence that fact overrides any idea that simple insulative
changes in hair length or conductance will protect against too much
CONDUCTIVE heat gain. In nature, black mammals tend to be either nocturnal
("solar avoiders") or they are creatures of the deep forest (who are
protected from the sun anyway). Rain forests, for example, are very, very
dark even on the brightest of sunny days (they have the awesome feel of a
moldering gothic catherdral). To give you some idea how dark: even on the
brightest summer day, a typical rain forest will be so dark that ISO/ASA
400 (rather high speed) film is barely adequate to capture an image
without a tripod.
A black dog (or a big, dark-coated mammal on a summer
day) benefits from short hair or even no hair at all. That's why Bison and
Musk Oxen (amongst others) shed. The reason: these creatures attempt to
cool through CONVECTIVE heat loss. Air, passing over the surface of the
skin, carries away the heat at the surface of the skin PROVIDED that the
air passing-by is cooler than the skin surface (otherwise, the skin
surface would gain heat from the hot air passing over it). Sunburn is
reduced in black-skinned creatures (melanin is protective to some extent
against ultra violet radiation -- but the NEW global conditions of our
diminishing ozone layer has made this relationship -- UV and melanocytes
-- a deadly one). Most mammals roll in dirt or mud for additional
protection against sunburn.
Some mammals (like us) have yet another convective
cooling trick. We sweat. An extra amount of energy is carried away from
the surface of the skin as liquid evaporates (changes state from a liquid
to a gas -- I think about 25 per cent more, but my physics is rusty. Too
much sweating I guess ). There is some draw backs: if the skin surface is
too wet, the surface water may act as a magnifyer (water bends light,
changing the skin's "refractive index"). Magnifying the sun's rays is bad
news. And in areas where the humidity is high (the air is saturated or
nearly so with water vapor), evaporative cooling loses its efficiency
dramatically.
Surface water cannot change state to water vapor is the
air above it is already full of molecules. So, mammals who live in Houston
must resort to air conditioners (chilling dehumidifyers) in office
buildings, period! Alternatively, move to Los Angeles where there's less
water vapor in the air (albeit other things like stray bullets seem to
fill the space between air molecules there.. :-).
By the way: sweating is best done when you cannot see
streams of water on the skin's surface. If the whole evaporative engine is
working precisely, a "damp" skin will have water molecules changing state
so quickly that the offensive streams of sweat will not be noticeable. We
humans, especially human males, sweat like stuck pigs in our youth, but
loose that ability to thermoregulate well when we age. Elderly people and
dogs have a lot of trouble with both heat and cold, so take extra care of
your aging canines (or people) in hot weather.
Thermoregulation aside, some dogs -- even those with
long, white, dry hair that slows heat gain -- like to be shaved down
because: (1) hair is heavy (shaving produces a feeling of freedom probably
much like taking off a tight wool jacket and running around with just a
t-shirt on); (2) hair, either matted or clinging to adjacent hairs quite
naturally, will tug on the skin's surface. That constant tugging as the
flank stretches and contracts during motion can really annoy some dogs.
And dogs, like people, will often do something (like really enjoy short
hair even in summer) that is not necessarily in their best interest.
Natural selection does not necessarily shape tastes appropriately
(consider that many primates will consume dangerously toxic foods or drugs
until they croak. The term "forbidden fruit" has a genesis quite far
removed from Genesis).
One of our little Cotons is Black & White. She is of
two minds in the bright summer sun. Her long, white, dry hair protects her
from heat gain while her prominent patches of long black hair fries her.
She succumbs to panting (a form of evaporative core body cooling) far
sooner than her light-coated daughter.
Incidently, you may see some black birds (like
redwings, starlings, or crackles) sitting in the sun, exposing their rumps
(a gland there needs sunlight) and panting like mad all the while. They
are technically "gullar fluttering" -- the equivelent of a mammal's pant
-- in an attempt to evaporate water on the tongue and cool their
skyrocketing core temperature. Some birds actually act drunk after long
exposure to the sun (their wee-tiny brains are truly addled). We had a
Coton who so liked to sun on hot days (Cotons were originally from a
desert area) that she'd practically fry her brain. We'd have to retrieve
her from the back lawn out of concern. Even long-haired bright white dogs
who know nothing about "Baywatch suntan envy" can overdo solar radiation
exposure when the sun angle decreases and solar radiation (called "insolation")
increases precipitously (summer).
A final point: dog breeds and mammal species who
normally dwell in far northern or far southern climes have had little need
to adjust to overly warm summers or to sun angles that reach the steep
angles we see in more equatorial regions. Take special care of these
creatures; it is we humans who have transplanted them outside their
element. So here's a few conclusions:
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Light-coated dogs with long hair are at an advantage
with respect to heat gain from the sun. If their coats are thinned (unmatted,
undercoat raked), they should do reasonably well with moderate heat and
solar exposure (no mammal sits on a sand dune in the sahara at midday in
the summer).
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Dark-coated breeds are in trouble in the sun. If
shaved, they risk burns. If adapted to polar regions, they should be
protected from our mid-latitude summer temps and insolation. Black-coated
creatures should avoid the sun.
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The nature of solar radiation has changed dramatically
since the 50s. All creatures, especially all mammals, are at risk of skin
cancer from solar exposure. The mutagenic effects of present day solar
radiation is a concern for all life forms (including plants). It's too bad
that we now must view the sun as a flying Chernobyl, but that's life on a
human-dominated planet.
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