A reader’s shorthair domestic tuxedo cat, the breed seen above, is in good health but has thinning hair on her shoulders and elsewhere. (Getty Images/iStock)

Dear Dr. Fox:

I find myself in need of advice concerning our 11-year-old shorthair domestic tuxedo cat. At her most recent physical a few months ago, the vet said everything was fine except for thinning hair on her shoulders, where there’s just a kind of downy fuzz instead of her black fur. The previous year, her thyroid test was normal.

The vet ran two tests on our cat’s fur: One was checking for mites or a similar problem; I can’t remember the other one. I recall she used a special light and magnifier, and she took a few hairs to check under the microscope. She said everything looked normal, and she couldn’t give any explanation for why our cat’s fur was not growing. She recommended Nupro supplements, which apparently provided good results for other patients. But after a few months, we still don’t see any improvement.

We have never seen our cat over-grooming or licking in those areas. She’s an indoor cat and is not exposed to anything outdoors. The thinning is on her shoulders, although her front legs are showing a bit of thinning. She eats Wellness CORE for indoor adult cats, and we give her the occasional Greenies treats for dental health, as well as Greenies Bites for Skin and Fur. Her litter box production seems normal.

She’s somewhat overweight, so we take her to be groomed two or three times a year because she has difficulty reaching her rear end to clean it. It gets shaved, and she also gets her nails clipped.

Since her last rear-end shave in November, the fur there has not grown back. So it’s not just her shoulders — presumably anywhere fur is removed, there’s no regrowth.

What can be causing this? Do you have any suggestions as to how to encourage fur growth? She does suffer from dandruff — always has, and nothing helps.

K.H., the District

DF: Because your veterinarian has wisely tested for thyroid disease and ringworm, I would consider the possibility of a chronic nutritional deficiency in omega-3 essential fatty acids.

Many dogs and cats show significant improvement in coat density and luster, as well as reduction of dandruff, after two to three months of dietary supplementation with fish oil. As long as your cat is not allergic to fish, one canned sardine a day might suffice. I would avoid all dry cat foods and canned foods that have rice and barley. There are freeze-dried and frozen cat foods in some stores now that provide good nutrition, and my cat food recipe (posted on my website, drfoxvet.net) might offer a long-term solution.

Dear readers:

In a new study, geneticist Bridgett von Holdt and colleagues compared the sociability of domestic dogs with that of wolves raised by humans. Dogs typically spent more time than wolves staring at and interacting with a human stranger nearby, showing that dogs were less fearful and more social than the wolves.

Comparative genetic analysis of those dogs and wolves, along with DNA data of other wolves and dogs, showed variations in three genes associated with the social behaviors directed at humans: WBSCR17, GTF2I and GTF2IRD1. Interestingly, all these are associated with the Williams-Beuren hypersociability syndrome in humans. Not all dogs, fortunately, are so affected as to become what I have long called “perpetual puppies.”

Michael W. Fox, author of a newsletter and books on animal care, welfare and rights, is a veterinarian with doctoral degrees in medicine and animal behavior. Send letters to Dr. Michael Fox in care of Andrews McMeel Syndication, 1130 Walnut St., Kansas City, Mo. 64106.

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