What is mastitis?
Mastitis is inflammation of the mammary gland, usually from bacteria entering through the teat. It affects dairy cows, goats and sheep, and can occur in animals nursing young as well as those milked by hand or machine.
It can reduce milk, harm the udder permanently and, in severe cases, make the animal very sick. Early attention gives the best chance of recovery.
Keep in mind that nursing does not protect an animal from udder problems. A doe or ewe whose young seem hungry, or who will not let them nurse, may have a sore udder. Check her udder at least once daily around kidding, lambing and weaning, when risk is highest.
- Can affect one or both halves of the udder
- May show no outward signs at first
- Can happen in nursing and milked animals
What signs should I watch for?
Look at the udder before and after milking. Heat, swelling, redness, hardness or pain are warning signs, and an animal may kick, resist milking or stand away from her young. Milk may look watery, clotted, stringy, discolored or contain flakes or blood.
Some cases are subclinical, meaning the udder and milk look normal but milk quality and production drop. A drop in milk or a change in the animal's behavior deserves attention.
- Hard, hot or swollen udder
- Clots, strings or color change in milk
- Fever, dullness, reduced appetite or lameness on the hind leg
What should I do first?
Call your veterinarian promptly if you notice signs. Severe cases can become life threatening within a day or two, especially in goats and sheep. Do not delay waiting to see if it clears up.
Separate the animal if you can, so she does not infect others, and milk her last or with separate equipment. Do not use milk from a suspected case for people, pets or other animals unless your vet says it is safe.
Write down everything you see: the date, which side of the udder, how the milk looked and the animal's temperature if you know how to take it safely. These notes are valuable to your vet, who will want a timeline. Keep the animal calm and comfortable and offer clean water while you wait for guidance.
- Keep notes on signs and when they began
- Do not give any medication unless your veterinarian directs it
- Wash hands and equipment well afterward
Why is a veterinarian needed?
Different bacteria cause mastitis, and the right approach depends on which is involved and how severe the case is. A vet may recommend a milk culture so treatment fits the organism, and can advise on withdrawal times so milk and meat stay safe.
Treating blindly can make the situation worse and contribute to drug resistance. Rules about milk sales and withdrawal periods are local and vary, so ask your vet and your state agriculture office.
Ask your vet about what to do with milk and meat during and after treatment. Withdrawal times are set to protect consumers, and the rules for selling dairy products are local and differ by state, county and product. Check with your state department of agriculture and your local health office before you sell any dairy product.
- Ask whether a milk culture makes sense
- Follow all instructions from your vet
- Ask about milk sale rules before selling anything
How does milking hygiene reduce the risk?
Clean hands, clean teats, clean equipment and a clean, dry place to milk reduce the number of bacteria that reach the udder. A consistent routine in the same order each time helps, and gentle handling avoids teat injury.
Extension dairy specialists recommend keeping bedding dry and clean, and keeping animals standing for a short time after milking while teat openings close.
- Wash and dry teats before milking
- Milk healthy animals first
- Clean equipment after every use
How can I prevent repeat cases?
Keep housing clean, avoid overcrowding, trim sharp hair around the udder where advised, and watch dry-off periods carefully, since that is a time of higher risk. Ask your vet about a plan for drying off and for monitoring.
Culling decisions for chronic cases are difficult and belong in a conversation with your vet. Keep records of every case so you can see patterns.
Keep a simple herd or flock log. Record each animal's udder checks, any off milk, treatments directed by your vet and results. Over time it shows which animals and which situations carry the most risk, and you can work with your vet on practical changes to housing, milking order and drying off.
Key takeaways
- Watch for heat, swelling, clots and changes in milk or behavior.
- Call your veterinarian promptly, since severe cases move quickly.
- Do not give any medication or use the milk unless your vet advises it.
- Clean, consistent milking habits lower the risk.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.