Frostbite

When a dog or cat is exposed to cold temperatures its body reacts in stages:

Your pet's fur provides insulation, just like us wearing a coat. Its hairs, when exposed to cold air, undergo pilo-erection. This is like you and I getting goosebumps. The hairs “stand up erect” trapping the air in that layer. This air is warmed by the body and adds additional insulation.
When the body's core temperature decreases, an involuntary reflex by the skeletal muscles known as “shivering” is triggered to generate heat and warm you up. Animals, like humans, experience this same reaction.
When the body is really getting cold and the animal's life may be at risk, the body responds by vasoconstricting the peripheral tissues. This means the body is being selective in where it is sending warm blood.
The organs are the most important to keeping an animal and human alive. If blood is not circulating in the core of the body (heart, liver, kidney, lungs, etc.), the body will shut down temporally by constricting blood vessels to the extremities until the body's normal temperature is attained.
By this stage, if a cat or dog has not received First Aid or warmth on it's own, frostbite will develop. Tissues that have frozen due to this response will die. Cats and dogs often experience frostbite on the tips of their ears, tails, face, footpads, legs and the genitalia in male dogs.
Frostbite can result in the loss of limbs, toes, and tips of ears.

Signs

Symptoms to look for if your pet has been outdoors and you suspect it may be suffering from frostbite.

Ice on body and limbs
Shivering
Tissues are bright red followed by pale color( vasoconstriction) to black color (death of tissue/ sloughing of skin)

First Aid

Warm the affected area rapidly with warm water using towels or warmed ice packs.
If it is a limb or paw that is frozen, soak it only in a bath or bowl of warm water.
Dry gently after you have the warmed the area.
Do not rub or massage the frozen tissue
Do not apply snow or ice
Do not immerse your pet completely in a bath this will cause the body temperature to decrease and cause hypothermia.

Prevent self-trauma

When the tissues are warmed it may cause some discomfort to your pet. The same also occurs when tissues are dead.

Wrap your pet in a blanket to prevent self-trauma and keep him or her warm.
Seek Veterinary care. Secondary infections can sometimes result from gangrene tissues.

What is Hypothermia?

Hypothermia is an abnormal lowering of the body’s temperature. This is a serious condition that can cause unconsciousness, shock and even the death of a pet. Pets that are outdoors in cold or subzero temperatures can become hypothermic.

If your pet shows signs of frostbite he or she may be also experiencing hypothermia. However do not rely on frostbite alone as an indication of hypothermia, as it can occur without the presence of frostbite.

Signs

Low body temperature (below 37,5) Take your pet’s temperature rectally! A lubricated electronic thermometer is easy to use.

Shivering
Weakness

First Aid

Warm your pet.
Use blankets.
Put warm water in plastic bottles then rap in towels to prevent burns.
Use plastic zip lock bags filled with uncooked rice that you warm in the microwave for 1-2 minutes then rap in a towel.
Micro wave ice packs that have not been frozen and rap in a towel.
If you use a heating pad never put the animal directly on the pad. Always use several towels. A weak animal will not be able to move and will suffer burns.
A hair dryer on medium warm is a quick start to warm up your pet while someone else is preparing blankets and water bottles.

Monitor your pet’s rectal temperature every 10-15 minutes.

When his or her body temperature is back to normal (38.5 C) stop warming. An over heated animal is just as dangerous.
Seek Veterinary care even if it looks like your pet is fine after you have warmed him or her. Kidney and bladder problems are common in pets that have been exposed to cold temperatures (infections).