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Some cats’ skin temperature affects their fur color

by Lee Pickett, VMD | July 5, 2021 at 1:49 a.m.

Q: Ruby, my Himalayan cat, was shaved for belly surgery. Her fur is growing back now, but it's darker than the surrounding fur. What can I do to prevent this from becoming permanent?

A: Don't worry, it's temporary. Enjoy her unique coloration while it lasts.

Ruby has "points," which means she has a pale trunk and darker ears, muzzle, tail, lower legs and paws. Dark points make the Himalayan, Siamese, ragdoll and similar breeds stunningly beautiful.

These points form in cat breeds that carry a gene mutation that affects the activity of an enzyme needed to create a dark pigment called melanin. The enzyme produces melanin at low body temperatures but fails to function at normal body temperature.

So, the body parts that are coolest — the points — produce more melanin and, therefore, darker fur than on the cat's warm trunk.

A Siamese cat has points — darker color fur on certain body parts, including the ears. (Democrat-Gazette file photo)
A Siamese cat has points — darker color fur on certain body parts, including the ears. (Democrat-Gazette file photo)

As an aside, cats with points are born white because the mama cat's womb is uniformly warm. As the cat ages, melanin is deposited where the body is coolest, giving rise to the striking coat pattern.

When Ruby was shaved for surgery, her bare skin was cooler than the surrounding skin, so more melanin was deposited in the fur that regrew. As that fur is shed, the new fur will grow in lighter, but it will take an entire hair growth cycle for her coat to return to normal.

Q: Our Yorkshire terrier Bentley has a dry, honking cough. His veterinarian said he has a collapsing trachea and recommended we walk him on a harness rather than a neck collar to take the pressure off his throat.

Is there anything else we can do to minimize his coughing and help him catch his breath? Please tell us more about this condition.

A: Collapsing trachea, also called tracheal collapse, is very common in toy and small-breed dogs like Yorkies.

The trachea, or windpipe, is a flexible tube made of cartilage rings that meet at a thin muscle called the trachealis muscle. The trachea collapses because the dog's cartilage rings are flattened instead of round and/or the trachealis muscle is so wide or pendulous that it sags into the trachea.

These characteristics result in a trachea that can't maintain its shape when the dog inhales and exhales, but instead narrows and collapses, producing the characteristic cough.

The most prominent clinical sign is an intermittent dry, honking cough. The cough, which usually occurs when the dog is breathing rapidly during excitement or exercise, is sometimes followed by retching.

If Bentley coughs when he's excited, help him relax until his breathing rate settles down.

Pressure on the trachea also can elicit the cough, which is the reason your veterinarian recommended a harness instead of a neck collar.

Fat in the neck and chest of an overweight dog presses on the trachea, worsening tracheal collapse. So, if Bentley is overweight, help him slim down.

Particles in secondhand smoke settle onto the furniture or floor, where Bentley probably spends most of his time. Smoke particles irritate a compromised trachea, so, if you smoke, you should quit or smoke only outdoors.

If these measures aren't adequate, talk with your veterinarian about medications, which are usually effective. If they aren't, your vet may recommend surgery.

Lee Pickett, VMD, practices companion animal medicine in North Carolina. Contact her at

vet@askthevet.pet

Print Headline: Fur color points form where cat's body is cool

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