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Why is my dog's milk green and leaking? Causes, mastitis, prevention.

Updated on September 23rd, 2025

Pet's info: Dog | Samoyed | Female | unspayed | 6 years and 4 months old | 50 lbs

Hi, I want to know whats the cause of toxic milk in lactating dog ? I used to give my dog tap water (in my country tap water is not safe for human) and the water smells like iron. i wonder if this is the cause? The dog milk turn a little bit green, and the milk start leaking 3 weeks prior to whelping.My vet examined the milk under the microscope and see bacteria in it. I forgot the name of the bacteria, it looked like many red dots. i want to prevent this in the future. Thank you

1 Answer

Most Helpful Answer

Dr. Strydom, DVM

Answered By Dr. Strydom, DVM

Veterinarian

Published on May 30th, 2020

The number one reason typically is mastitis from E. coli bacteria. It is not from the water. It is likely just from the surrounding environment as E. coli is everywhere. Dogs that do this are prone to do it again with subsequent litters so be aware of that. The antibiotic of choice for this problem is Trimethoprim Sulfa. She should be treated now and if you breed her again, she should start the antibiotic one week before her due date and continue for two weeks after whelping.
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