Thoroughbred Stud Farm Stallion Nominations

   Home > Equine Diseases - Mastitis


Equine Mastitis is a bacterial infection and inflammation of the udder. The mare's udder is divided into halves, each containing two quarters (similar to a cow). The two quarters on a side, however, feed into a single teat with two openings, rather than individual teats as the cow has.

Acute equine mastitis occurs occasionally in lactating mares, most commonly in the drying-off period, in one or both glands.

Pathogens responsible for causing equine mastitis:

• Streptococcus zooepidemicus (most pathogen)
• Streptococcus equi
• Streptococcus equisimilis
• Streptococcus agalactiae
• Streptococcus viridans
• Gram negative bacteria

Penicillin used to be the main antibiotic used to treat equine mastitis but a broader spectrum antibiotic is needed now to combat the vaster range of pathogens.

The udder is divided into halves and each half consists of quarters. Equine Mastitis usually affects one or two quarters of the udder, on the same side. Rarely two quarters on opposite sides are affected.

The equine mastitis infection results from a bacterial invasion that causes the affected quarter to become hot, swollen and painful.

In horses, the udder is much smaller and protected than the more pendulous udders of cattle. The teat canals and openings are therefore also smaller, making infection less likely. Interestingly neither age, pregnancy, or past parturient status greatly effects the incidence.

There is another way that equine mastitis can manifest itself. It gradually develops producing a fibrosis that destroys the mammary tissue. If the mare is has strong immunity, the equine mastitis will clear up by itself. Most cases will however need medication.

• Mare be go off her food
• Udder is visibly swollen and hot
• Depression
• Feverish
• Mare may kick foal when nursing
• Standing off balance
• Holding stifle out away from body.
• Milk from the infected side changes consistency to either lumpy viscous milk or watery fluid
• Abscesses can form requiring surgery.
• Occasionally equine mastitis can become so severe, the udder tissue is completely destroyed and cause death.

• Trauma to udder – causing an open wound allowing infection to spread (e.g. kick from horse, insect bites)
• Dirty Bedding can contaminate the open wound
• The mare may be more susceptible to infection
• Oestrogen levels can affect the prevalence of mastitis
• Excess oestrogen enlarges the mammary glands and produces milk when no there is no viable pregnancy


- Pathogen causing the equine mastitis must be determined in order to treat with antibiotics.

- Many pathogens can be responsible so a broad spectrum antibiotic is given. Previously penicillin was the only one given.

- The teats must be hand milked frequently to reduce the swelling and pressure.

- Hot packs and non-steroidal anti-inflammatory medications may also help reduce the pain and swelling.

- With antibiotics mastitis is easily treatable in horses, the course of treatment must be completed or there is danger of a relapse.

- If prompt action is taken, the infection could be reduced to normal within a week.
- Permanent damage is unlikely if correct treatment is administered.



Contact Us | Home