F500
Mastitis

Introduction: Mastitis, or inflammation of the mammary gland, is the most common and the most expensive disease of dairy animals, including dairy goats and sheep, throughout most of the world. Although stress and physical injuries may cause inflammation of the gland, infection by invading bacteria or other microorganisms (fungi, yeasts and possibly viruses) is the primary cause of mastitis.

The impact of mastitis goes with the milk beyond the gate of the farm. Changes in milk composition (reduction in calcium, phosphorus, protein, and fat; and increases in sodium and chlorine) reduce its quality. In addition, the antibiotics used in treating mastitis are an important industrial and public health concern. The presence of antibiotic residue in the milk interferes with the manufacturing process of many dairy products (cheese and other fermented products). Undesirable flavors reduce the value of dairy products and the presence of low levels of antibiotics may cause health problems in consumers.

Clinical and Subclinical Mastitis: In clinical mastitis, the infected udder often becomes swollen and painful to touch. The milk is visibly altered by the presence of clots, flakes, serum, and sometimes blood. In severe cases (acute mastitis), the ewe/doe has a fever, rapid pulse, loss of appetite, and a sharp decline in milk production.

In contrast, subclinical mastitis is subtle and more difficult to detect. The animal appears healthy, the udder does not show any signs of inflammation, and the milk seems normal. However, microorganisms and white blood cells (somatic cells) that fight infections are found in elevated numbers in the milk.

The loss of milk and income due to clinical mastitis are readily apparent because milk production drops sharply and milk from animals treated with antibiotics must be discarded. However, a lot more milk is lost due to subclinical mastitis:

Control of subclinical mastitis is more important than simply treating clinical cases:

Development and Transmission of the Disease: Infections begin when microorganisms penetrate the teat canal and multiply in the mammary gland. The teat itself is the first line of defense against the penetration of bacteria into the udder. Normally, the sphincter muscle closes the teat canal tightly when the ewe or doe is not being milked.

Invasion of the teat most often occurs during or right after milking. Organisms present in the milk or at the teat end are propelled into the teat canal and cistern when there is admission of undesired air in the milking unit. This happens when the milking unit slips or squawks, or when the teatcup is removed without first shutting off the vacuum. After milking, the teat canal remains dilated for 1-2 hours and the canal of a damaged teat may permanently remain partially open. Organisms from the environment (feces, bedding, etc.) or those found on injured skin at the tip of the teat may easily invade an open or partially open canal.  

Bacteria first damage the tissues lining the large milk-collecting ducts. While in these ducts, the bacteria may encounter leukocytes (white blood cells) that are naturally present in small numbers in the milk. These cells are the animal’s second line of defense because they can engulf and destroy bacteria. However, during this process, the leukocytes release substances that cause the movement of additional leukocytes from the blood into the milk. This increases the somatic cell count in the milk.

If the bacteria are not entirely destroyed, they continue to multiply and begin to invade smaller ducts and alveolar (small cavity or sac) areas. Milk-secreting cells damaged by toxins and other irritants release substances that lead to increased permeability of blood vessels. Additional leukocytes move to the site of infection. They enter the alveolar tissue in great numbers by squeezing between the damaged milk secreting cells. Fluids, minerals, and clotting factors also leak into the affected area. Clotted milk may close ducts and, in effect, isolate the infected regions.

Sometimes, the microorganisms are eliminated rapidly and the infection is cleared. In these cases, the clogged ducts are opened and milk composition and production return to normal within several days. However, if the infection persists and ducts remain clogged, the entrapped milk causes the secretory cells to revert to a resting (non-producing) state and the alveoli begin to shrink. Substances released by leukocytes lead to the complete destruction of alveolar structures and replacement of the alveoli with connective and scar tissues. The destruction of milk secretory tissue could be called the animal’s third line of defense to bring the infection under control.

If the infection is not treated, the number of somatic cells in the milk becomes elevated and a reduction (potentially permanent) in milk yield can result.

Causative Agents/Treatments: Mastitis is an infection of the udder caused by two major categories of bacteria:

  1. Highly Contagious - These are passed from animal to animal, usually during milking.
  2. Environmental - These bacteria are usually found in a manure contaminated environment.
  1. Contagious: Treatment of CONTAGIOUS bacteria depends on the specific organism causing the problem. Most of these infections are subclinical; therefore, additional testing is required to detect the problem. Gram positive bacteria are the most common causes of infection.

    There are three major bacteria in this category:
    1. Streptococcus agalactiae - This organism must live in the mammary gland.
      • Treatment for this bacteria is usually done one animal at a time with an appropriate antibiotic. Many intramammary products are effective (Today and Tomorrow). Some effective injectable antibiotics may include penicillin and Gallimycin, with consideration of withholdings. This is one of the only bacteria that can be SUCCESSFULLY REMOVED from a herd.
      • Control of this problem centers around the milking parlor and milking procedures (teat dipping, milking machine surveillance, milking hygiene, and dry animal treatment).

    2. Staphylococcus aureus - This organism is found on workers’ hands and equipment that are contaminated with milk from infected animals.
      • Treatment for this organism can include the use of intramammary tubes and other injectable antibiotics. However, this bacteria is extremely difficult to eliminate because it causes micro-abscesses in the mammary tissue that prevent the antibiotics from reaching the bacteria.
      • Control of this problem includes teat dipping, washing hands/equipment properly, and a good dry treatment program. Infected animals should be grouped together and milked last.

      * Because this organism is so difficult to eradicate, it is recommended that culling of affected animals be an essential part of a herd management program.

    3. Mycoplasma - This organism is usually introduced into a herd through replacement animals. The respiratory tract of young animals can also be a hiding place for the organism. Infection with these bacteria often cause joint swelling and a yellow/grainy discharge from the udder. Many of the Mycoplasma organisms that cause mastitis in sheep and goats are not common to the United States.
      • Treatment with antibiotics is very ineffective. Culling of affected animals is the ONLY means of eradication.

      * Special culture techniques for Mycoplasma are not routinely used unless requested; therefore, the laboratory should be informed each time a milk sample suspected of containing Mycoplasma is sent.

  2. Environmental: Environmental bacteria are more likely to cause clinical signs and even death. Preventing these infections involves keeping the bedding and sleeping areas clean and dry. It is also important to keep the teats and teat ends free from injuries. Areas where the animals are confined should be worked on a regular basis to keep the soil dry and exposed to sunlight. Following are two major categories of environmental bacteria:

    1. Environmental streptococci
      • Treatment of these bacteria usually involves intramammary dry treatment tubes and/or injectable antibiotics.
      • Use a combination of injectable and intramammary antibiotics. Some research indicates this is necessary for total elimination of this problem.
      • Control of this problem involves keeping stalls and sheds as clean as possible (manure free).
      • Proper hygiene is beneficial, although control of this organism is difficult because it is found in the environment.

    2. Coliforms - These include E. coli and Klebsiella and are generally gram negative. The milk is generally watery and serous (slightly blood tinged and sticky).
      • Treatment involves controlling the side effects of the infection within the animal:
        • Frequent milking, with oxytocin given just prior to milking, is very beneficial.
        • Anti-inflammatory agents (Banamine) are also recommended. These reduce the fever and have an anti-endotoxin effect.
        • Administration of oral or intravenous (IV) fluids may be required if dehydration is a concern. See page C115 and F145.
        • Antibiotics can also be implemented to prevent systemic or whole animal infections. See Section H.
        • In cases of severe infection, dexamethasone may be necessary.

  3. Other Causes of Mastitis:
    1. Actinomyces pyogenes - This usually results in a very foul smelling, custard like discharge from the udder. This disease is usually not very contagious and affects only one animal at a time.
      • Treatment may involve penicillin and frequent milkings.

    2. Gangrenous Mastitis - This problem can be caused by many organisms. The milk is usually watery, and the teat itself can be cold to the touch. Many times gas is present when milking out the udder. At this point, the animal is often very sick and/or down.
      • Treatment is very aggressive and involves anti-inflammatory agents, fluids, and injectable antibiotics like penicillin. The use of steroids and/or udder amputation, under the direction of a veterinarian, may also be necessary in severe cases.

    3. Retroviral Mastitis ("hard udder") - This condition is thought to be associated with caprine arthritis-encephalitis (CAE). Studies show that when CAE is removed from the flock or herd the problem is removed. The signs of this infection usually appear right after the doe gives birth. Her udder becomes very firm and produces little, if any, milk. Different from bacterial cases of mastitis, udders infected with CAE are not hot or red. The doe will sometimes come back into milk after several weeks.
      • Treatment - There is no successful treatment for this problem, so culling is recommended. If this problem is suspected, entire herd testing for CAE may be necessary (see page F105).

    4. Pseudomonas, Mycobacterium, Pasteurella, Brucella, Corynebacterium pseudotuberculosis, and other Staphylococcus organisms are sometimes the cause of mastitis.

Diagnosis: There are many different types of tests (C.M.T., strip test, and culture and sensitivity on the milk) that can identify mastitis in an animal. Some tests can also identify the bacterial cause of the mastitis. See Section D for additional information on the above tests.

Mastitis Prevention:
  1. Ensure that the animals and the environment are clean: Be emphatic about corral and barn cleaning and maintenance. Clean each area as often as 3 times a day if necessary.

  2. Maintain regular milking machine maintenance: Have a routine check of the entire milking system at least every 6 months by a qualified technician. Use high quality inflations and change them regularly.

  3. Insist on good milking procedures: Use gloves, forestrip each half of the udder, pre-dip each teat, and wipe each teat with individual towels. Do not over-milk or under-milk, and always post-dip. Have fresh feed in the mangers after the animals leave the milking parlor. This will keep the animals standing until the teat sphincter constricts and the post-dip has dried.

  4. Have a written dry animal program that is followed: Utilize intramammary antibiotic infusions based on culture and sensitivity results (see page D135). Maintain clean conditions, particularly in the birthing areas.

  5. Realize that nutrition can play a significant role in preventing mastitis: Supplements such as zinc, vitamin E, selenium, and biotin are helpful for mastitis prevention. Consult a nutritionist for additional details.