Endurance.Net Ridecamp Archives

Hi Kathy,

>     I’m going to try uncovered next
>     time, and just stop & check him on the way home to see if he’s
>     shivering at all, and if he is I’ll cover him up.
>      
>     Kathy

If your horse is shivering, do not be so quick to put on that blanket.

Mammals have two physiological methods of maintaining a high enough
temperature in the cells near the surface of their body.  One is shivering
and the other is the contraction of a tiny muscle at the base of each hair
follicle causing the individual hair to rise up.  This latter allows the
hairs all together, the coat, to form a "blanket" that traps a lot of air.
Air is a lousy conductor of heat so this natural blanket keeps the heat in 
and the cold out.

Shivering is "high amplitude, low frequency, muscle contractions".  ATPs
(Adenosine tri phosphate) are high energy compounds found in the body.
When a mammal shivers, the fuel for these muscle contractions is ATP.  As
the muscles use and break down ATP, one of the byproducts is heat.

So, if the ambient temperature is sufficiently low (and this temperature
will be higher if the mammal is constrained and cannot move about, as in a
trailer), the animal will shiver to raise its surface temperature and the
hair follicles will raise each hair to trap the resulting heat.  These
physiological activities are NORMAL and not uncomfortable.  Obviously, when
shivering becomes extraordinarily violent there is a problem namely that
the body's thermo regulator (shivering) isn't working well enough but that
is not what we are talking about here.  And as to why we humans are so
uncomfortable when we shiver, well... WE HAVE NO BODY HAIR.  All we get are
goosebumps and our heat escapes into the air.  We shiver more, more
goosebumps, more heat loss.  Until we throw on a "blanket" to trap all that
nice heat, we continue to shiver and get colder.  Brrr...

So IF the temperature is low enough, ALL mammals will shiver to create body
heat at the surface of their bodies.  Whether you put a blanket on or not,
your horse will shiver because the blanket itself does not produce heat,
the shivering does.  The blanket just traps that heat and it does a rotten
job at it compared to a horse's natural blanket, the aforementioned coat.
The blanket YOU put on has no "temperature dial".  It cannot release some
heat when necessary.  As some of the heat from inside your horse's core
moves outward, adding to the supply at the surface, the blanket won't let
that heat escape so... your horse's body goes into cooling mode, ie, it
sweats.  Unfortunately, the blanket screws that up too.  It traps heat AND
it traps the moisture from the sweat.  Sweat cools a body when it
evaporates but the blanket won't allow evaporation.

On the other hand, your horse's coat DOES have a "temperature dial".  When
the surface temperature gets high enough, the shivering stops.  Then, as
the heat from the core moves outward, raising the temperature of the skin,
the hair follicles relax, allowing heat to escape into the cooler air of the
trailer.  A gentle cycle is set up.  Skin cools, shivering plus hair
raising start, correct temp is attained, shivering ceases and here the hair
relaxes and raises to adjust the skin temp as heat rises from the horse's
core till the surface temp drops low enough to prompt shivering again.

Only if the horse is overheated do you have a problem (which is why in
cooler temperatures you should NEVER put a horse away hot, not in a trailer
and not in a stall).  If the horse is overheated, a lot of core heat will
try to work its way to the surface.  The skin and hair get overloaded with
heat and the horse starts to sweat to get rid of the excess heat.  The
cooling progresses too rapidly and the SKIN, NOT THE CORE, get too cold and
the shivering starts and the hairs go up to trap heat.  So now you have
heat trying to get out and the skin physiology trying to retain heat.
BAD!!  Adding a blanket to this mess can be disastrous because the blanket
cannot POSSIBLY allow heat to escape fast enough to cool down the core.
The horse sweats profusely (that is its only cooling mechanism) to no
avail.  The horse cooks inside.

Just remember, shivering is NORMAL and it is a mammal's PRIMARY way of
raising its surface temperature.  That temperature can also be raised by
running around a lot and raising the core temperature, but as a survival
tool, that is wasteful and in a trailer, impossible :)  Shivering (heating)
is also not uncomfortable, any more than sweating (cooling) is
uncomfortable.  Only when shivering becomes (or is from the getgo)
unproductive does it cause discomfort.





=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Ridecamp is a service of Endurance Net, http://www.endurance.net.
Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp
Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp

Ride Long and Ride Safe!!

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-