Mastitis in dogs

Written by Dr Andrew Miller MRCVSDr Andrew Miller MRCVS is an expert veterinary working in the field for over 10 years after graduating from Bristol University. Andy fact checks and writes for Pure Pet Food while also working as a full time veterinarian. Pure Pet FoodPure Pet Food are the experts in healthy dog food and healthy dogs featured in media outlets such as BBC, Good Housekeeping and The Telegraph. Working with high profile veterinary professionals and nutritionists, Pure Pet Food are changing dog food for the better. - Our editorial process

Mastitis is an infection or the inflammation of an animal’s mammary glands, which are the glands located in the breasts. The condition doesn’t occur in dogs quite as often as it does in other animals, such as cows, but a dog affected can experience potentially fatal implications.

Although it’s most often reported in pregnant and female dogs nursing their puppies, it can actually impact any dog, surprisingly even males.

If you’re breeding your dog, it’s especially important to be aware of mastitis, what the signs are and what to look out for after they’ve given birth so you can catch and treat the infection before it advances.

What is mastitis in dogs?

There are two types of mastitis, the first of which being galactostasis, which typically affects dogs who are late into pregnancy or the new mums who are weaning their pups off their milk.

Galactostasis happens because too much milk has been produced and retained inside the teat. There will be no infection here, and your dog probably won’t show any other warning signs of the illness except pain and sensitivity. This form of mastitis is relatively uncommon.

Acute septic mastitis is the second and more serious form of the condition. This occurs when bacteria somehow enters the teat canal, travelling all the way up to the mammary gland and creating the infection.

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Usually, Escherichia coli, Staphylococcus sp. and Streptococcus sp. are the most likely bacterium that create the infection. The impact of the condition can vary from a minor, localised infection to something as severe as a life-threatening systemic infection.

What dogs are the most prone to developing mastitis?

Any breed of dog at any age can experience mastitis, it’s just the most prevalent in nursing or pregnant dogs. Both new mums and experienced mothers can experience it and the size of the litter has no impact on the development of mastitis either. Dogs having small or large litters are prone to the condition.

With a smaller litter, the mammary glands are more likely to become swollen with excess milk building up, but with a larger litter the openings of the teats remain open for longer, making them much more susceptible to bacteria entering.

A study looked into the incidence rates of mastitis in a cohort of dogs, with 13.2% of whelpings subsequently diagnosed with mastitis which was around 408 cases overall. On average, the typical day of diagnosis was around 16.7 days postpartum.

What causes mastitis in dogs?

Generally, mastitis is commonly seen in the postpartum period when too much milk accumulates in the teat without being removed. This can happen due to sudden weaning, when the pups move onto real food so they’re not drinking the female’s milk anymore, or if the new mum sadly loses one of her pups. In both scenarios, less milk will be taken and cause a build-up.

Mastitis can also be triggered following trauma to the teat which allows for bacteria to infiltrate and cause infection.

Unsanitary conditions can also play a big role in the development of mastitis in dogs that aren’t pregnant or nursing, as bacteria and other irritants will be prevalent in unhygienic areas. This means that the whelping box (a den prepared for your dog’s birth) and the place where the pups sleep must be kept clean and dry, ensuring that any soiled bedding, towels and tissue paper is removed quickly.

What are the signs and symptoms of mastitis in dogs?

When mastitis is in its early stages, your dog might not seem poorly at all. As it progresses, you might notice that the mammary glands become:

  • Swollen

  • Inflamed, red and sore-looking

  • Discoloured (red, purple or blue/black) as the tissues die and blood supply is decreased

  • Scabbed over

  • Sensitive to touch

  • Different in texture and firmness

  • Hot to touch

Also, if you suspect mastitis, try and get a look at the milk she expresses to her pups. It may be cloudy, thickened in consistency, lumpy or contain visible blood and pus. As the infection advances, you might notice your dog becoming increasingly more lethargic, develop a fever, lose their appetite and even begin vomiting as the infection spreads throughout their bloodstream and begins to become septic.

How is mastitis in dogs diagnosed?

It’s likely that your vet will be able to diagnose mastitis based on the physical signs alone.

Tests may be required, such as a cytology of the secretions from the gland to identify the infection. A cytology of the milk involves collecting a tiny sample of the milk from the infected gland and placing it under a microscope to search for pus. Pus is the liquid that accumulates at the site of the infection, and it’s comprised of dead white blood cells. The presence of white blood cells proves that your dog is suffering with mastitis.

Blood tests can also be taken to see if the mastitis has started to spread to other systems in the body, along with an ultrasound to determine how much damage has been done to the mammary gland and how far it’s progressed through the body. Treatment will then be prescribed by your vet based on these tests.

How is mastitis in dogs treated?

With relatively mild cases, antibiotics provided at home should be enough to resolve the infection, alongside some pain meds to make your pet more comfortable. The vet will need to take nursing puppies into account, as some antibiotics can cause issues to the pups as the drugs can be transmitted to them through the milk.

Therefore, you’ll need to keep an eye on the puppies while your dog is on the medication, look for changes in weight, stools, how much they eat and their energy levels.

In some cases, your dog might not respond to the antibiotics, in which case the vet might take a bacterial culture. This involves collecting a sample of the milk and sending it off to be tested. The sample will be isolated and an antibiotic sensitivity test will be taken to detect which antibiotic treatment will be the most effective in treating your dog’s mastitis.

In extremely severe cases, hospitalisation may be required to keep your dog on an intravenous drip.

Can I help to treat my dog's mastitis at home?

Your vet may recommend that you express your dog’s milk by hand from the affected mammary gland to ease the swelling, promote blood flow and just make them more comfortable. Ask your vet to demonstrate how best to do this.

Also, warm compresses using towels will help to decrease the pain and inflammation. Using cabbage leaves as a compress is widely recommended for the same reasons, you’ll just need to secure the leaf to the gland using either a bandage or tight t-shirt.

Can mastitis in dogs be prevented?

Like many infections, you can’t really prevent mastitis from developing. The only thing you can really do if your dog is pregnant or nursing is to constantly check that everything’s running smoothly.

Look out for any subtle signs of change, whether that be a change in the mammary glands, your dog’s reaction to your touch, or a change in the milk expressed. Frequently try and express some of their milk by hand so you can regularly observe the milk’s quality.

Daily weigh-ins of the puppies, even more so in their first week of life is an extremely useful way of detecting an issue. If the puppies are dropping in weight or struggling to maintain it, it’s a tell-tale sign there could be a problem. The earlier you spot the infection the easier it will be to treat.

What is the outlook for a dog with mastitis?

As with any illness, the earlier it’s diagnosed the more effective treatment will be. Within about 2-3 weeks of necessary treatment, the mammary gland should be as good as new and functioning normally. However, in cases where the disease has advanced and spread to other systems in the body, your dog could be severely ill for a long time.

Permanent damage can sometimes happen, leaving the affected gland incapable of producing milk at all, which is why early detection is so vital.

What happens to the puppies?

Of course, the puppies are the best at getting all the milk out in an effective and efficient way, much better than hand-milking. However, the mum can sometimes be in too much pain to allow the pups to nurse, or there could be a worry about the antibiotics she’s been prescribed being dangerous for the puppies, so hand-feeding will be the only option per your vet’s guidance. Weigh and check over the pups daily to ensure they’re getting enough nutrients this way.


The signs of mastitis should be pretty visible and clear to see, so hopefully you’ll be able to get your dog treatment before the condition advances too far and causes your dog some serious discomfort.

  1. New insights of canine mastitis ‒ a review Animal Science Papers and Reports, 36, (1), Jan 2018, 33-44
  2. Incidence and risk factors for canine mastitis and metritis in two guide dog populations Animal Reproduction Science, 231, Aug 2021,