Cow Udder Swelling: Causes, Mastitis Risk & What to Do

Udder swelling in cows has several possible causes, and the timing matters. A common noninfectious cause is udder edema, which is often seen just before or after calving, especially in first-calf heifers and high-producing dairy cows. This swelling is usually fairly symmetric, feels cool to mildly warm, and may not be very painful. Merck notes that physiologic udder edema is common around parturition and can become a herd-management issue when severe enough to interfere with milking.

A more serious cause is mastitis, which is inflammation of the mammary gland. Mastitis may be caused by bacteria and can make the udder feel hot, firm, painful, or lumpy. Milk may look watery, thick, clotted, flaky, bloody, or otherwise abnormal. Cornell and Merck both describe mastitis as one of the most important and common diseases affecting dairy cattle, with effects on comfort, milk production, and culling risk.

Trauma is another important cause. Fence wire cuts, hoof treads, abrasions, insect bites, machine-milking injury, and teat wounds can all cause localized swelling. Merck also notes that teat injuries and structural udder problems can increase mastitis risk because damaged tissue and abnormal teat canals make infection easier.

Less common but important causes include teat obstruction, abscesses, skin disease, suspensory ligament breakdown, and emerging infectious problems that can affect milk and udder health. Because these conditions can look similar early on, a swollen udder should be assessed in context: when the cow calved, whether one quarter or the whole udder is involved, what the milk looks like, and whether the cow seems systemically ill.

See your vet immediately if your cow has udder swelling plus fever, depression, weakness, dehydration, refusal to eat, rapid drop in milk production, foul or bloody milk, or a very hot and painful quarter. Deep wounds, active bleeding, a teat laceration, or swelling that comes on suddenly after trauma also need urgent attention. Merck specifically notes that lacerations involving the large milk vein are emergencies because severe hemorrhage can occur.

You should also call your vet the same day if one quarter is much larger than the others, the udder is too swollen to milk normally, the calf cannot nurse, or the milk contains clots, flakes, watery secretion, or pus. These signs fit clinical mastitis or significant udder injury more than simple edema.

Careful monitoring at home may be reasonable for mild, even swelling around calving when the cow is bright, eating, afebrile, and producing normal-looking milk. Even then, keep a close eye on comfort, milk flow, and whether the swelling is improving over 24 to 48 hours.

If you are unsure whether the swelling is normal postpartum edema or early mastitis, it is safest to involve your vet early. Delays can mean more udder damage, more discarded milk, and a harder recovery.

Your vet will start with a history and physical exam. They will ask when the swelling started, whether the cow recently calved, whether one quarter or the whole udder is affected, what the milk looks like, and whether there has been trauma, nursing problems, or changes in milk yield. They will also check temperature, hydration, appetite, and signs of systemic illness.

Next, your vet may strip and examine milk from each quarter and collect a sterile milk sample for culture or other testing. This helps separate mastitis from edema and can guide treatment choices. Cornell highlights the value of pathogen-based mastitis management, and Merck notes that mastitis cases vary widely in severity and cause.

If trauma is suspected, your vet may examine the teat canal, look for lacerations, bruising, or hematoma formation, and determine whether the quarter can still be milked safely. Superficial wounds may be cleaned and protected, while deeper wounds may need prompt repair. Merck advises that deeper udder and teat wounds are best treated quickly, often within hours, to improve healing.

Treatment depends on the cause and severity. Your vet may recommend more frequent milk-out, anti-inflammatory medication, intramammary therapy, systemic medication, wound care, culture-guided changes, or supportive fluids in severe mastitis cases. They will also review milk and meat withdrawal times, because treated cows may need milk discarded for a period to avoid drug residues.

Home care depends on the cause, so start by checking in with your vet if the udder is painful, hot, or producing abnormal milk. For mild postpartum edema, supportive care often focuses on gentle, regular milk removal, keeping the udder and teats clean, and reducing anything that makes swelling worse. Merck notes that severe edema can interfere with cluster attachment and milk flow, so practical milking support matters.

Keep bedding clean and dry, because dirty, wet environments increase mastitis pressure. Watch for changes in appetite, attitude, temperature, and milk appearance at every milking. If the udder is so swollen that the calf cannot latch well, your vet can help you decide whether temporary assisted nursing or hand-milking is needed.

If there is a superficial skin wound, follow your vet's instructions for cleansing and topical care. Do not place unapproved products into the teat canal or udder. With any medication, use only products and routes approved or specifically directed by your vet for food animals, and follow all withdrawal times.

Do not use milk from an affected or treated quarter for people unless your veterinarian confirms it is safe and legal to do so. The AVMA recommends pasteurization of nonhuman mammalian milk sold or distributed to consumers, and milk from cows with mastitis, blood, or drug residues should not enter the food supply.