Mammary Gland Hyperplasia in Cats

Mammary gland hyperplasia is a relatively uncommon condition in cats.  One or more mammary glands swell up due to hormonal changes thought to be associated with progesterone levels.  I have seen this condition develop most frequently a few weeks after a young queen is spayed.  It may also develop in intact females after their first heat cycle during pseudopregnancy.  Male and female cats exposed to human progesterone creams may experience mammary gland enlargement. Pictured below is a young cat who developed mammary gland hyperplasia and mastitis about 3 weeks after her spay.   

Treatment for mammary gland hyperplasia involves removing the source of progesterone.  In my experience, most glands will slowly shrink until they are back to normal in 3 weeks.  The exception to this is with exposure to human progesterone creams.  It may take up to a year for the glands to revert to normal after exposure.  The cat pictured above made a full recovery with antibiotics and warm compresses to treat the mastitis.  We also expressed the infected gland once per day to decrease pressure.  It seemed to make her feel better.  For animals in which sterilization is not an option, drug therapies are available to help decrease progesterone concentrations. 

Published by kristennelsondvm

Dr. Kristen Nelson grew up on a farm in Watertown, Minn., where she developed a deep love for animals of all kinds. She received a Doctor of Veterinary Medicine degree from the University of Minnesota, College of Veterinary Medicine. Kris then completed a small-animal internship at the prestigious Animal Medical Center in New York City. In addition to writing and speaking, she cares for small and exotic animals in Scottsdale, Az. Dr. Nelson is widely quoted in the media. Her credits include Ladies’ Home Journal, USA TODAY, the Los Angeles Times and numerous radio and television interviews. Dr. Nelson has written two books, Coated With Fur: A Vet’s Life and Coated With Fur: A Blind Cat’s Love. Kris and her husband Steve share their home with rescued cats, birds and a dog.

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