Answer by Researcher pinkfreud on Mon 5 Nov 2007 - 10:07 pm UTC:

There are two kinds of sweat glands: apocrine (or epitrichial) glands and
eccrine (or atrichial )glands. Dogs have both.  When it is said that dogs
sweat mainly from their foot pads, this refers to the eccrine glands. Since
dogs do not sweat as a method of regulating their body temperature, the
amount of fluid that a dog loses by sweating is small.

"Each day a dog loses water through its urine, feces, saliva, breath, and
sweat. Unlike humans and horses, dogs do not lose much water due to
sweating."

Hydration Strategies for Exercising Dogs
http://www.hydrolyte.us/Arleigh%20Reynolds-Hydration%20Strategies.pdf

"In dogs the secretions of the sweat glands do not have a perspiration
function (thermoregulation). In dogs, sweat is believed to have pheromonal
and antimicrobial properties. (Scott, 2001; McEwan Jenkinson, 1989)"

http://publications.royalcanin.com/renvoie.asp?type=1&cid=107653&id=102348

"Do dogs sweat?
Yes and no. The dog's dermal skin layer has two types of glands that
produce fluids. The apocrine glands, which produce sweat in humans, have
two other functions in dogs — they help seal the outer layer of the
epidermis and they secrete pheromones that give dogs a distinctive body
odor. The eccrine glands in the pads of the paws do produce a watery
secretion similar to human perspiration. This secretion leaves damp
pawprints behind nervous or stressed canines and may also improve traction
for a quick getaway."

Canis Major: Canine Skin
http://www.canismajor.com/dog/skin1.html

"Dogs do not produce sweat for thermoregulation. However, they do have
sweat glands, called apocrine glands, associated with every hair follicle
on their body. The exact function of these is not known, but it is
suspected that these are meant to produce pheromones or chemical signals
for communication with other dogs. These sweat secretions probably produce
an individual odor signal that is recognizable by other dogs.

Dogs also have sweat glands on the pads of their paws and on their noses.
These are eccrine glands. When these glands are active, they leave the nose
and pawpads slightly moist and help these specialized skin features
maintain their functional properties. The odor associated with dog paw pads
is much more noticeable on dogs with moist paw pads than on those with dry
pads.

Dogs also have numerous apocrine glands in their external ear canals. In
this location they are referred to as ceruminous glands."

Wikipedia: Dog Odor
http://en.wikipedia.org/wiki/Dog_odor 

Dogs also sweat from their nether regions:

"Apocrine sweat glands in the circumanal glands of the dog appear to be
more active than those on the general body surface in terms of apocrine
secretion, exocytosis, and the release of multivesicular bodies. Shed
secretory cells containing large granules, as well as degenerated
polyhedral cells from the circumanal glands, might contribute, to some
extent, to the subtle composition of sweat from these apocrine sweat
glands."

Apocrine sweat glands in the circumanal glands of the dog
http://www3.interscience.wiley.com/cgi-bin/abstract/5004754/ABSTRACT?CRETRY=1&SRETRY=0


"Sweat glands are of two types: apocrine and eccrine. Apocrine glands are
tubular glands with a coiled secretory portion and a long straight duct
that empty into the follicular infundibulum. In domestic animals, all hair
follicles have apocrine glands. Apocrine glands in dogs and cats are also
present in association with the anal sac, and modified apocrine glands,
known as ceruminous glands, are present in the external auditory meatus."

Merck Veterinary Manual
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/72208.htm

I hope this is helpful!

Best regards,
pinkfreud