NEWS
Mastitis in mares
Posted: Saturday, December 31, 1994
If not treated promptly, mastitis can cause lasting damage and even deathHorses have fewer udder problems than other domestic animals such as cows, sheep, or goats, but when mastitis occurs in a mare it can be quite serious, and veterinary attention is often needed.
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.
Mastitis usually affects one or two quarters of the udder, on the same side. Only rarely are two quarters on opposite sides affected, or all four quarters.
The infection results from a bacterial invasion that causes the affected quarter to become swollen, hard, and warm. Infection also causes the milk (if the mare is lactating) to change consistency-it may become lumpy, thicker, or more watery than normal.
Traditionally, mastitis has been associated with lactating mares, especially at weaning time when the mare has a full udder that may be painful and slow to dry up. Symptoms of mastitis may develop any time up to eight weeks after the foal is weaned. But a mare does not have to be lactating to develop mastitis. Even maiden and barren mares occasionally acquire infections in the udder, due to trauma or insect bites.
Causes
A 1989-'90 study at the University of California, Davis, Veterinary Hospital, looking at mares with mastitis, revealed that 28% were not lactating at the time of infection. Of the mares examined, 44% were lactating when the infection began, and another 28% developed mastitis within eight weeks of weaning their foals.
The study also showed that 71% of the cases occurred during the summer fly season-evidence that insects could be possible sources of infection. The inflammation may be triggered by fly bites and other external irritations of the teat opening.
Mastitis development in a non-lactating mare may also be due to abnormally high estrogen levels in her system. This excess female hormone can result from a pituitary gland tumor or lush spring pasture (or legume hay) that contains high levels of estrogen. High estrogen concentrations can cause mammary gland enlargement and trigger the production and secretion of milk, even though the mare is not pregnant and has not foaled. If the non-lactating mare begins to secrete milk due to excess estrogen, she may become a candidate for mastitis.
Udder injuries, such as a kick from another horse or insect bites, contamination of the udder from dirty bedding, and inherited susceptibility to infection may all be factors that can lead to mastitis.
Symptoms
Mastitis symptoms may be quite obvious or very subtle, depending on the severity of the infection and the amount of pain involved. A mare may kick at her foal when it tries to nurse, and an alert horseman may notice that a mare with mastitis does not seem quite right. She may stand off balance and rest one hind leg (trying to ease the swollen side of her udder) or hold her stifle out away from her body.
Signs of mastitis include swelling of the udder, heat and pain, and edema in the surrounding area. Usually only one teat is affected, but sometimes both are. Some mares become depressed, feverish, or go off their feed. The foal may avoid nursing from the infected teat because the milk tastes different, and that side becomes even larger, adding to the mare's discomfort.
Acute mastitis causes a hot, painful udder, and in a lactating mare with a severe case, the milk from the infected side may be just a small amount of watery fluid. Some mastitis cases form abscesses in the udder and nearby lymph glands, which require surgical drainage. Occasionally mastitis completely destroys the udder tissue and can cause death of the mare.
Other cases may develop gradually, producing a fibrosis that slowly destroys the mammary tissue. Some milder forms of mastitis may clear up without treatment-if the mare's body defenses are strong enough to combat the invading organisms. But most cases will need medication.
Diagnosis and treatment
Tissue smears or cultures of milk samples from the affected area can help the veterinarian determine the specific pathogen causing the infection, and antibiotic sensitivity tests can be done to find the most effective antibiotic for treatment. Treatment may consist of antibiotics given systemically (such as intramuscular injections) and in severe cases a mastitis medication may need to be squirted directly into the affected part of the udder through the teat canal.
Treatment will also include frequent hand-milking of the affected side of the udder to hasten the elimination of infection and abnormal milk. Hot packs and non-steroidal anti-inflammatory medications may also help reduce the pain and swelling. The antibiotics should be given for at least 5-to-7 days. If halted too soon, the infection may recur. But with prompt and appropriate treatment that is continued long enough to completely halt the infection, most cases of mastitis improve a great deal within 2-to-3 days, and the udder will generally return to normal within a week.
Penicillin was traditionally the standard treatment for mastitis, but since a number of different bacteria are now recognized as capable of causing the infection, veterinarians are moving to a two-phase treatment. A broad-spectrum treatment with a trimethoprim sulphonamide combination is usually begun immediately to start fighting the infection while waiting for the results of the culture, cell study, and sensitivity tests. Then after the specific bacteria are identified and the best antibiotic selected for continuing treatment, the veterinarian may switch drugs.
In addition to antibiotics, other treatments can help the mare recover more rapidly and comfortably. If the mare is lactating, she should be milked out five or six times every 24 hours to get rid of the infected milk and hasten the production of normal, healthy milk. If local antibiotic treatment is given (infusing the drug directly into the teat), it should be administered twice a day (immediately after milking out) and the udder gently massaged to help distribute the medication through the quarter. Treatment should continue until the milk dries up (after weaning) or returns to normal.
Commercial preparations for cattle can be used in treating mares, if necessary. Select the proper type according to whether or not the mare is milking.
You can reduce swelling and discomfort by applying hot packs to the udder for 15-to-20 minutes at a time, 2-to-3 times a day. Usually a combined treatment of systemic and infused antibiotics, along with frequent milking and hot packs, is the most effective treatment for mastitis.
If the mare is nursing and her udder is painful, the nursing sessions should be supervised to keep her from kicking the foal. The infected milk will usually not harm the foal, and if the foal will nurse the affected side, it will save you the task of milking it out.
Proper and prompt treatment of mastitis will reduce the chance of permanent damage to the udder. Longstanding or recurring cases, however, may prove more difficult to clear up and may be due to abnormalities in the teats themselves.
Prevention
To help prevent serious mastitis cases, check udders often and be aware of each mare's udder appearance-note abnormal changes, especially in lactating mares. Avoid unnecessary handling of the udder, and make sure your hands are clean (or wear sterile gloves) when you do handle it.
If flies are problematic, bring mares and foals inside during the most troublesome periods of summer. And after weaning, observe the mare's udder closely for several weeks (and do not milk her out). Reducing or eliminating the grain ration at weaning time may help the mare cut down more quickly on her milk production. Some horsemen limit a mare's water intake to about five gallons a day for a few days to help decrease the milk flow.
If a mare has a serious case of mastitis during one lactation, you will not know until her next foaling whether or not the affected quarter will produce milk again. It all depends on whether the mammary tissue was damaged.
As she nears her next foaling date and the udder fills, you will be able to tell-a damaged quarter that is not producing milk will not fill, and the udder will appear lopsided. If more than one quarter is damaged, you may have to find another milk source for the foal.
Mastitis is not common in mares, but it occurs often enough to be a concern to horsemen. If the infection is detected early, the udder can usually be treated vigorously and its functions kept from being permanently damaged.
Heather Smith Thomas is a free-lance writer based in Salmon, Idaho, specializing in veterinary and breeding topics.
