Udder Issues for the Mare

Take any swelling, asymmetry, or other abnormality of your mare's udder seriously.

A few days after weaning your foal, you notice his dam's udder is hot and tender. While this veteran broodmare's udder has been quite large at weaning time before, she's never been so grumpy about having it touched. A veterinary examination confirms your suspicions: The mare has mastitis. Udder problems such as this are not terribly common, but if you own or manage a broodmare you should be aware of the following issues.


The most serious udder problem in mares is acute mastitis, which is an infection of the mammary gland that occurs most commonly after weaning. "This can be life-threatening but is usually treatable, especially if the owner realizes what's happening early on," says Jon Palmer, VMD, associate professor of medicine and director of the Neonatal and Perinatal Programs at University of Pennsylvania's New Bolton Center Connelly Intensive Care Unit, in Kennett Square. "If the veterinarian does a physical exam it becomes obvious that the mammary gland is infected."

Clinical signs of acute mastitis include depression and high fever, although Ahmed Tibary, DVM, professor of theriogenology at Washington State University's Department of Veterinary Clinical Sciences, notes that signs can be variable. The udder might be slightly enlarged or very tight and painful to the point the mare is lame and reluctant to move. "There may be asymmetry (one side larger than the other), or some exudate (pus) or lesions on the udder," he says. Another sign of mastitis in a mare whose foal is not yet weaned is reluctance to let the foal nurse--for example, kicking at the foal.

When diagnosing mastitis, the veterinarian should carefully inspect and palpate the enlarged mammary gland. He or she might ultrasound the gland and run culture on the secretions and examine them microscopically to search for bacteria.

Mastitis requires aggressive treatment to avoid further complications and loss of mammary function. "Treatment is often difficult," says Tibary. "We usually try to strip out the milk and give anti-inflammatory medications and systemic antibiotics. We use local injections if possible, but the anatomy of the mare's mammary gland does not lend itself very well to these."

Bill Tracy, who manages Eureka Thoroughbred Farm near Fredericksburg, Texas, says treatment can be very difficult if the mare is in pain and/or hasn't been handled much. If you've never handled the mare's udder, you can't expect her to stand quietly for milking or mastitis treatment--and even then, if the udder is painful she might be difficult.

"If you are medicating the mare, make sure the medication is not being ingested by the foal," Tracy adds. "If the mare has mastitis on both sides, the foal will need an alternative source of milk."

To prevent mastitis development, "you want the mare to dry up as quickly as possible" after weaning, says Tracy. "Keep her outside with plenty of exercise. Reduce her nutritional intake for a week or so. We only give the mares enough (feed or hay) to keep them coming up from the pasture so we can monitor them."

Some people believe they should milk out the mare themselves because her udder is so large and uncomfortable. "This is the worst thing to do," cautions Tracy. "It just prolongs the ordeal of drying up. After a week or so, the udder should begin to shrink. If it's still huge at that time, have your veterinarian examine it more closely and make sure the mare doesn't have mastitis."

Dirty Udder

One of the most common udder problems stems from owners failing to clean the area properly. "Some people rarely look at the udder when grooming or washing a horse," Tracy notes. "Mares and fillies, even weanlings, can accumulate a lot of gunk (a mix of dirt, sweat, and oil) up between the teats. It can become thick, crusty and hard, and irritating. You may have to pick or scrape it off."

A common sign of a dirty, irritated udder is tail rubbing, which the filly or mare might do in an effort to alleviate itching.

Keep the udder/teats clean using warm water without soap (which can further irritate that delicate area, alter the normal bacterial flora, and possibly result in a fungal or bacterial infection) to get rid of irritating debris. To make udder cleaning safe and effective for all involved, handle and touch fillies' undersides and teats as you groom and train them. "Fillies may be sensitive about having their udders touched," says Tracy. "They may kick if you're not gentle about it."

When Tracy teaches young horses to tolerate bathing, he sprays water gently over their legs and body and up under the udder. "This helps familiarize them with being touched in that area," he says. "It provides the sensation of being touched and you are well out of reach if they try to kick."

This approach will be beneficial later, if you ever have to milk a mare or help her foal nurse.

Once you clean a broodmare's udder and it's full and producing milk, it tends to stay clean, Tracy notes. "Most of the problems are when the mare is not producing milk and the udder is empty; debris gets caught between the flaccid teats," he says.

Edema Before Foaling

Some mares develop fluid swelling (edema) around the udder before foaling because the blood supply and lymphatic system both change their course during this time. "There are some large blood vessels on the ventral (lower, or underside) abdomen when the mare is not lactating," says Palmer. "Blood (normally) drains from the ventral abdomen up through the inguinal (groin) area. When the udder develops and there's a need for more blood supply and more return of that blood, those blood vessels not only get larger but also reverse their flow."

So instead of draining blood toward the udder and groin area, the large vein (superficial caudal epigastric vein, also called the "milk vein") drains blood toward the abdomen and front of the body, causing edema. It is typically more extensive during a mare's first pregnancy.

"After she's had a lactating udder, it's easier to adapt," Palmer explains. "Another thing that contributes to swelling or edema toward the udder is the heavily pregnant uterus, lying on the ventral abdomen. This also blocks some of the lymphatic drainage and blood flow, with added pressure on the vessels."

Some cases become so severe that the mare starts leaking blood along with the milk. "These mares are a concern because if there's blood in the secretions they may be rupturing the suspensory ligament of the udder," says Tibary.

Cold hosing/cold compresses and systemic anti-inflammatory drugs might help reduce swelling, but the best way to relieve this condition is with exercise, which helps stimulate blood circulation and lymphatic drainage. If the mare is kept in a stall or small pen, she should be turned out.

"It's remarkable how much edema the mare can have in the morning when you turn her out, and when she comes back in at night the swelling is gone," notes Palmer. "People may think the udder is shrinking, but it's not; this is just the edema around it."

If a nonpregnant mare develops edema in and around the udder, the swelling might be part of the larger complex of edema resulting from disease. "For example, if there is edema (extending down) the entire limb this may be indicative of equine infectious anemia or equine viral arteritis," says Palmer. "Some viral diseases will cause increased edema in the mammary gland."

Lack of Milk

Sometimes a mare does not produce milk when she foals, a condition called agalactia. "Fortunately we can use a drug called domperidone," says Palmer. "It stimulates release of hormones, such as prolactin, that triggers milk production and aids in udder development."

Veterinarians also administer domperidone to mares that have grazed endophyte-infected fescue pastures and don't have milk at foaling. "The toxin in the fescue prevents the udder from developing because it prevents prolactin release," Palmer says. "The domperidone reverses this problem."

First-time dams or nervous mares might not produce milk either; a tense mare is less likely to let down her milk. "We generally give these mares a little oxytocin," says Tracy. "It's a naturally occurring hormone triggered by the foal nursing and helps stimulate milk production and let-down."

Mares with pituitary pars intermedia dysfunction (PPID, or equine Cushing's disease) that are on a drug called pergolide might also have problems producing milk. Pergolide inhibits mammary gland development and prevents the mare from preparing to foal. "In that situation the owner has to take the mare off pergolide for awhile to let the udder develop," says Palmer. "Putting the mare on domperidone while she's still on the pergolide is counterproductive."

Be sure to discuss domperidone or any other medication administration for a PPID-affected mare with your ¬veterinarian.

Other Problems

Abscesses, including those related to pigeon fever, form occasionally in udders.

Injuries sustained from kicks to the udder or, for instance, jumping a fence and landing on it can occur. "A nonlactating mare has a small udder with less blood supply and is less vulnerable to serious injury--though the injury still may become infected and have a hard time healing," says Palmer. "At least it is located ventrally on the body, with good drainage, which can be helpful during healing."

Lesions similar to summer sores can appear on teats due to fly bites.

Leaking milk is fairly common and might occur as some mares resume cycling after winter anestrus (noncycling period). Tibary notes that this can result from a combination of the mare's cyclicity and lush early spring pastures that might contain plant estrogens. "This is linked to an increase in the hormone prolactin when the mare begins her seasonal cycles--and the mammary gland starts developing," Tibary explains. "Sometimes the mare bags up but doesn't have real milk, just a serous (clear, runny) secretion. Others may actually produce milk."

Malformed teats, such as inverted or too-small teats, are rare in fillies and mares. It's important to remember, however, that the udder has four quarters, and each teat has two openings. When checking the udder, both sides should look and feel the same. If the udder seems lopsided or painful, this might indicate a problem. Some mares also have enlarged teats, which can be difficult for a foal to latch onto, especially when they are first nursing. Monitor these foals closely to ensure they ingest sufficient milk.

Neoplasia, or tumors, of the mammary gland, including melanomas, can be "relatively aggressive," says Tibary. "We also see some adenocarcinomas (cancer originating in glandular tissue) and occasionally cutaneous lymphoma (cancer of the lymphatic system) in the udder."

Nonfunctional (dead) teat is one scarred from a previous episode of mastitis so the mammary tissue on one side might produce milk but it can't come out. In other cases the damage is so extensive the affected side of the udder does not produce milk at all.

Bacterial infection can contribute to udder enlargement or inflammation.

Witch's Milk describes secretions from a filly's teats starting at birth and lasting for a few days, due to the affect of the dam's hormones on the foal before birth. While this typically doesn't cause problems, "the situation can become complicated if you try to milk or touch the mammary gland and it becomes infected," Tibary cautions. "The enlargement of the filly's udder should also be differentiated from other possible problems such as hernias or other abnormalities of the ventral abdomen."

Take-Home Message

Although often out of sight, a mare's udder needs cleaning and careful attention, particularly at foaling and weaning. These are the times problems are most likely to pop up. Contact your veterinarian at the first signs of swelling, pain, or abnormalities in this area to keep both mare and foal healthy.


Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.