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Veterinary Topics: Mastitis in mares

Posted: Saturday, June 07, 2003

Weaning is the most common time to find inflammation of the mammary glands

BROODMARES have fewer udder problems than cattle or goats because their udders are smaller and less apt to be bruised or contact dirty bedding, manure, and other contaminants. When mastitis--inflammation of the mammary glands often due to infection--does occur in a mare, it can become quite serious unless treated.

The mare's udder is divided into halves, each half containing two portions called lobes or quarters. The two lobes on each side feed into a single teat, with two openings. Mastitis usually affects one or two lobes on the same side; only rarely are lobes on opposite sides affected. Infection often results from bacterial invasion, causing the affected side to become swollen, hard, and warm. If the mare is lactating, her milk may become lumpy, thicker, more watery, or tinged with blood.

How to treat mastitis

• Administer intramuscular injection of combination of penicillin and gentamycin for at least five to seven days.
• Hand-milk affected side of the udder to hasten elimination of infection and abnormal milk.
• Encourage mare to exercise.

Ahmed Tibary, D.V.M., Ph.D., associate professor of theriogenology at the veterinary teaching hospital at Washington State University, said the most common cause of mastitis is infection.

"It's more often a direct, primary infection, rather than spreading to the udder from another part of the body, but this can happen also," Tibary said. Most often the cause is trauma (such as bruising of the udder) or contamination (insects chewing on the teats, parasites, etc.). Sometimes an aggressive foal that bunts the udder too hard during nursing can bruise the mammary tissue, leading to infection.

David Unnerstall, D.V.M., who has an equine practice near Dallas, said mastitis occurs most commonly in lactating mares. "I see it most often at foaling and at weaning," Unnerstall said. "Some mares, especially older ones, get enlarged teats at foaling, and the young foal may find it difficult to nurse."

Tibary said, "Sometimes the mammary glands' cisterns [reservoirs for holding fluid that are normally small in mares] become very large and accumulate a lot of milk that stays there for a while." If the foal has trouble getting on the large teat and just nurses one side, the unnursed teat becomes even larger and that half of the udder may develop mastitis.

"Any time you see a mare not letting the foal nurse--such as biting, kicking, or chasing him--be suspicious that she has a sore teat," Tibary said.

"Make sure the foal nurses both sides," Unnerstall said. "If he doesn't, you'll have to milk out the large teat. I've seen some situations where it took a lot of active management to prevent mastitis in that half of the udder. Foaling time is when you'll encounter this problem in an older mare with baggy teats, but it can happen any time during lactation."

The most common time to find mastitis is at weaning, when the udder becomes large and tight--and more easily bruised. But, a few cases occur in maiden mares or dry mares. Sometimes mastitis is not due to bacteria, but to larvae of flies or parasites (especially during summer), even in mares or fillies that are not lactating.

Some cases in fillies or dry mares are caused by high levels of estrogen, causing production of serum in the udder. Fillies might develop an udder that becomes tender and uncomfortable, said Unnerstall. "If they start leaking a little serum from the teats and there are flies chewing on the teats, it is possible to get an infection in the udder," he said.

Tibary sees four or five cases a year in maiden mares that start producing serum from the teats. "Flies or insects are attracted to the serum," he said. "The common thought about mares or fillies lactating in spring [even though they have not foaled] is that it may be due to a combination of the seasonal effect on their hormones, and the lush green pasture."

Pain and swelling

One of the main signs of mastitis is a hard, firm udder that is warm to the touch. The mare could resent having it touched.

"Pain and swelling are the usual symptoms, but in some cases where the mare has had a chronic mastitis, there may just be an asymmetry of the gland; one side of the udder is larger than the other," Tibary said. "Sometimes the side that is smaller is nonfunctional due to earlier damage from the mastitis."

Signs of mastitis depend on the severity of infection and amount of pain. A nursing mare might kick at her foal when it tries to nurse. The foal might avoid nursing the affected teat because the milk tastes different.

In either case, that side of the udder becomes larger, adding to the mare's discomfort. If the udder is quite sore, she might stand off balance, resting one hind leg or holding that stifle away from her body so it does not touch the swollen udder.

Some mares become depressed, feverish, or go off feed. In severe cases, milk from the infected side could be just a small amount of watery fluid. Abscesses might form in the udder and nearby lymph glands, requiring surgical drainage. Occasionally, a serious case completely destroys the udder tissue and could cause death of the mare. Other cases might develop gradually, producing a fibrosis (thickening and scarring) that slowly destroys the mammary tissue.

Tibary said severe cases that flare up quickly might produce a hind-leg lameness or ventral edema (swelling along the belly). "I've seen some cases where edema affected the hind legs, extending down both legs," he said. "In some of these, you may even see the beginning of cellulitis [acute inflammation of the deep subcutaneous tissues, sometimes with abscess formation]."

Tumor, abscess, or mastitis

Swelling in the udder might be due to other things, said Tibary. "Mastitis is probably the most common cause of problems in the mammary glands, but there have also been a few cases of mammary tumors reported," he said. "So it is very important to determine whether the enlargement is from mastitis or a tumor." Have a veterinarian look at the mare and make a proper diagnosis.

"A milk sample for cytology and culture can give an indication of whether it's a bacterial infection," Tibary said. "If you see neoplastic [tumoral] cells, this would indicate a tumor. The veterinarian will feel the udder to see if the mammary tissue is uniform or has lumps and bumps. An ultrasound examination can give a more precise look at the mammary gland and tell you if there's a disturbance in the tissue structure--to help you diagnose an abscess versus simple mastitis. Ultrasound can also help you tell the difference between a tumor and an abscess.

"If we see a lesion, aspiration with a needle or a biopsy can help us know whether it's an abscess or tumor," Tibary continued. "If there's pus, then the best thing to do is drain the abscess. It's almost impossible for a mammary abscess to break and drain on its own.

"These need to be drained and treated, even if you must destroy part of the mammary tissue [and lose the production from that part of the udder]. An abscess generally has to be opened and drained out the side of the udder, rather than through the teat."

Antibiotic treatment

Administering a combination of penicillin and gentamycin is the most common treatment for mastitis, Tibary said. "We generally treat the mare systemically [with an intramuscular injection]," he said. "Treating the udder itself is very difficult in the mare, much more so than in the cow. People have used the same mammary preparations used for cows with relatively good success but, if I am going to be aggressive with an acute mastitis in a mare, I do both.

"To get results with systemic treatment, you must use an antibiotic that can reach the local tissue," Tibary continued. "One that does this fairly well is TMS [trimethoprim sulfadiazine] in combination with penicillin and gentamycin; it has a large spectrum of effectiveness for different types of bacteria. In one case, we used a preparation we use systemically in cows, which is ceftiofur, which has a very broad spectrum."

The antibiotic should be continued for at least five to seven days. But, with prompt and appropriate treatment that is continued long enough to halt the infection, most cases improve greatly within a few days, and the udder will generally return to normal within a week. Treatment includes frequent hand-milking of the affected side of the udder to hasten elimination of infection and abnormal milk.

The mare should be milked out every two to four hours. If a local antibiotic treatment is infused directly into the teat, it should be administered twice a day and given immediately after milking out that teat. Treatment should continue until the milk dries up--if the foal has been weaned--or returns to normal.

Some people try to help the drainage by giving the mare oxytocin, said Tibary. "Using hot packs on the mammary gland, or warm water from a hose, will help reduce the pain and inflammation and make it easier to milk," he said. "One method is to use bran for the hot pack, and microwave it so it keeps the heat longer. Hold that around the udder.

The hot pack or hot soak should be done for 15 to 20 minutes at a time, two or three times a day.

Unnerstall uses warm water to help soften that half of the udder. "Use enough pressure [low-pressure warm water stream from a hose] that it does some good, without so much pressure to cause discomfort," he said. "Anything that breaks up the hardness of the udder will make it easier to milk out. Once we get the udder softened up, we milk out the clots and curdled milk. If you catch it early, there might just be a little off-color [orange] or curdled milk in the first few squirts and then you'll get clear milk. Make sure you are getting milk from both quarters on that side, and not leaving the front or rear quarter full of infected milk."

Tibary pointed out that exercise is important for the mare. "Don't keep her confined in a stall," he said. "If she has an acute inflammation, she will be reluctant to walk. Give her some anti-inflammatory medication to ease the pain so she'll walk more. I like to use Banamine, because it gives you a very good start at reducing the inflammation during those first couple of days."

If the mare is nursing a foal and her udder is sore, supervise nursing sessions to keep her from kicking the foal. "You also don't want the foal to nurse the affected quarter if she is shedding a bad type of bacteria," Tibary said. "You may need to put the foal on milk replacer, or make sure he only nurses the good side while you keep the other side milked out."

Prompt and proper treatment will reduce the risk of permanent damage to the udder. Longstanding or recurring cases could prove more difficult to clear up. "If you have a nasty case with abscess formation, surgical removal of the whole gland may be indicated to get rid of the infection," Tibary said. "You may have to condemn that half of the udder. In some cases, you need to do more blood work to see if there's toxemia, particularly in acute cases. These can become life threatening, creating toxemia and laminitis."

If a mare has a serious mastitis, you will not know until her next foaling whether the affected side will produce milk again, even if you clear up the inflammation. As the mare nears her next foaling and her udder fills, a damaged side that is not producing milk will not fill and the udder will appear lopsided.