From Janet Tobiassen Crosby, DVM,
Your Guide to Veterinary Medicine.
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A viewer writes:
My wife and I had a discussion whereby I said that two dogs of the same breed, health status, age & fitness, but one being a dark colored coat & the other being a light colored coat, the lighter colored dog would be able to withstand more exposure to the daylight hours of summer versus the other dog being a darker colored coat. Is this true? Does the color of the coat of a dog make much difference in the dog-days of summer? Please advise a couple of dog & cat lovers!

The color of the coat does make a difference -- in a couple of ways.

First, the heat of summer. Just like humans wearing dark clothing, the effect of the heat will be more noticeable in the hot rays of the sun. The dark colors absorb the heat more than light colors, which reflect the heat away. For the record, ALL pets, regardless of coat color, should always have access to cool shade and fresh cool water in the summer heat! A dog house out in the sun doesn't count, either. Those dog houses can heat up more than the ambient temperature, even though they provide shade.

Secondly, coat color can make a difference when thinking about the damaging effect of the sun's UV (ultraviolet) rays. Lighter colored animals are much more prone to sunburn and skin cancer than their darker colored companions. Cats, dogs, and horses that spend a lot of time in the sun and have a light colored coat or lacking the black pigment around the eyes, ears, and nose, can get sunburned. Cats in particular, love "sunbathing", as any cat lover knows! Long term effects of sun exposure may include skin cancers such as squamous cell carcinoma and malignant melanoma.

So what can you do to protect your pet? Here are some options:

• Provide easy access to cool shade at all times.
• For horses with sensitive eyes, a fly bonnet can be used to protect from the sun.
• Sunblock can be used -- depending on the pet and the location of sensitive skin. Note: cats and dogs are quite adept and licking topical lotions and cremes off, so speak to your veterinarian as to what would be appropriate for your pet. Ingestion of a topical lotion might be worse than the sun exposure, so use caution.
• For very sensitive animals (white/albino with lots of pink, hairless skin areas), tattoos can be applied to provide some protection from the sun. This should be done by your veterinarian! Talk to your veterinarian if you feel your pet is a extra sun-sensitive animal.

For additional "keep cool" tips, please see this article:
"Tips for keeping your pet cool and comfortable".

The Dog Days of Summer
So what exactly does the term "dog days of summer" mean? I always envisioned languid dogs hanging out under the shade tree, waiting for the cool of the evening, but in reality it has to do with the star Sirius, the dog star, which is part of the Canis Major (big dog) constellation. The word "Sirius" is from the Greek word for scorching or burning. In mythology, it is also the name of Icarius' dog, who was changed into a star.¹

Sirius the star is the brightest star (second to the sun) in the sky and ancient people thought that this star added to the summer heat of the sun. So how exactly do dogs fit in the picture? According to this source on Wikipedia:

The Ancient Greeks referred to such times in the summer as dog days, as only dogs would be mad enough to go out in the heat, leading to the star being known as the Dog Star. Consequently, the constellation was named after it, as a Big Dog.

Hopefully you and your dog are staying cool in the summer heat!

Reference
Sirius¹: Sirius. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc. http://dictionary.reference.com/browse/Sirius (accessed: July 31, 2007).