4831. VET CASE. Pyometra in a 14-year-old Jack Russell. Mammary tumours in non-spayed female dogs.

Pyometra in a 14-year-old Jack Russell. Brownish red vaginal discharge was seen during consultation. The dog's spay would be postponed till the antibiotics cleared the pyometra (infection of the uterus). 

https://youtu.be/XREF37vbycg

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What causes mammary tumors in dogs?
Mammary tumors develop because of spikes in female hormone (estrogens) that take place during a dog’s heat cycle. By spaying a dog at 6 months of age or before the first heat cycle, it virtually eliminates the risk of getting mammary tumors, which starts at only about 0.5%. Once a dog goes through one single heat cycle, the risk increases to 8%. After a second heat cycle, the risk shoots up to 26% (says the American College of Veterinary Surgeons).

If a dog is spayed after 2 years of age, then there is no more protection. Over 25% of non-spayed female dogs will develop mammary tumors. This is a huge percentage! Being obese or receiving hormones (estrogens, progesterone) can further increase that risk.