Mastitis and other mammary gland problems in the mare

Last Updated on April 9, 2022 by Allison Price

Although mammary gland problems are rare in mares, they can cause abnormal milk production, discharge, swellings or lumps.

Two mammary glands are present in the horse, and there are two teats. This is in contrast to four teats for cows. A horse milking technique is different from a cow. There are two holes at the tip of each teat, which don’t always point in a single direction. It can be difficult and messy to collect milk in a jug for a foal. If you find yourself in this situation, contact your vet or produce shop for advice and possibly a’milking apparatus’.


Mastitis is rarely seen in mares. However, it can happen in maiden mares and barren mares as well as mares who are feeding foals, after the death of foals, or after weaning. Mastitis can be described as a large, painfully swollen mammary gland, hot, and often bloody discharge from the teats. A mare may feel sick or have a fever.

Antibiotics are used to treat the problem. The vet may need to take a sample from milk to culture the bacteria.

Although hot packs and cabbage leaves can help reduce swelling, they are difficult to apply and take time. Cabbage leaves work as a poultice to draw fluid from the swollen tissue. It is easier to apply cabbage leaves if the patient is wearing a brace.

Most mares will heal with the right treatment. It is rare for it to recur, but it is possible.

An abscess may develop in the mammary. Abscesses can be painful and require either lancing or long-term antibiotics. While this is not a common problem in Australia, it can occur more often overseas due to ‘Pigeon Fever ( Corynebacteria fauxtuberculosis), or Tuberculosis(Mycobacteria species).

Abnormal Milk Production

“Bagging up” is a term that describes mares whose mammary cells are growing due to increased glandular growth and milk production.

This is a normal process in a mare who is preparing for a foal. It usually takes place in the two weeks before the foal is born. ).

Running or dripping milk before the foal is born is not a normal procedure. This is because the foal’s small amount of colostrum (or ‘first milk’ which contains protective antibodies for the foal) is losing on the ground. Once the foal is born, it is at high risk of developing infections such as joint ill, umbilical Abscess, pneumonia and septicaemia. If your mare has ever given birth to a foal, you should consult your vet.


Your vet should be notified if your mare is ‘bagging up’ when the foal’s due date is less than three weeks away. An early mammary growth can indicate problems with your foal (i.e. A placenta infection, twins, or a miscarriage can all indicate problems with the foal. To save the pregnancy, medication and veterinary intervention are often necessary.

Sometimes, even if a mare is not pregnant, they start to produce milk. This could be due to abnormal hormone production by one of the hormone-producing glands in the body (i.e. Secondary to Cushing’s Disease. It can sometimes be caused by a tumor forming in the affected gland. Ingestion of phyto-oestrogens, hormones found in plants, is another common cause. Some clover varieties can act as milk-producing hormones for horses. In this instance, changing the food source is usually enough to fix the problem.

Lumps, bumps, and ulcers

‘Smegma is a normal buildup of crusty material, which can sometimes be found between the mammary glands. This is a normal accumulation of skin cells, sweat, dirt, and can be easily wiped away. There should not be pus or ulceration of underlying skin.

Ulceration looks like ‘exposed flesh’. It tends to be sunken beneath the skin’s level and not raised like a lump. This is particularly concerning for white or pink unpigmented skin. A vet should examine these lesions immediately. There is another possibility: Summer sores are caused by Habronema worm larvae being dropped by flies. This usually causes a local reaction. This reaction can also be caused by Pythiosis, a fungal-like organism (or’swamp carcinoma’).

Lumps Always have your lumps examined by a veterinarian. It is difficult to tell what they are by just looking at them. We often need to perform a biopsy (biopsy) in order to determine if they will be a problem. Sarcoids and other types of cancers are two common causes of lumps in this region. soft tissue sarcoma). Melanomas can be found in grey horses but are not as serious as sarcoids or sarcomas.

Swelling at the front of the mammary cells is common in late-term mares. This is simply fluid that has accumulated under the skin and is not draining well. The lymphatic system has been stretched, and the baby is blocking good drainage. It usually disappears within a few hours after birth. It should not be painful and will indent if you press down with your finger. It may be a more serious problem if the mare is unwell or feels pain when you press firmly. A ruptured tendon or protein loss may be a sign that the mare needs to be examined by a veterinarian.


Once, I was called to check on a pregnant mare with blood from her teat. It looked like dried blood when I examined it, but the mare was chestnut and had chestnut-coloured teats. This was due to the exfoliating of chestnut-coloured cells within the developing mammary gland. The teats were small and not painful.

The bottom line is to always contact the vet if your mare is having trouble breathing, dripping milk before giving birth, or if her mammary glands become swollen or painful.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!