Understanding Mastitis in Dairy Cows: Causes, Diagnosis, and Economic Impact

1. Unit Animal Science

2. Problem Area Growth and Development of Animals

3. Lesson Testing for Mastitis

4. Student Learning Objectives • 1. Understand how various bacteria can cause mastitis. • 2. Know the difference between the clinical levels of mastitis. • 3. Correctly use the CMT in the diagnosis of bovine mastitis. • 4. Appreciate the economic importance of mastitis to the dairy producer.

5. Terms • Somatic cell count • Staphylococcus aureus • Streptococcus agalactiae • Subacute • Subclinical • Anorexia • Antibodies • Chronic • Inflammation • Leukocytes • Mastitis • Peracute • Phagocytes

6. How do various bacteria cause mastitis? • Mastitisis an infection of the udder caused by a bacteria that can easily spread from one cow to the next. • A. Bacteria can be spread by improper sanitation of milking equipment or by injury or chilling of the udder. If not treated, mastitis can be fatal in cows. Disease prevention is the key to animal health management. Prevention is often more beneficial, and cheaper, than treating an outbreak of the disease. • Somatic cell count, or the number of infection fighting cells present in the milk, is a good indication of the presence of infection. The greater the number of somatic cells, the more likely infection or disease is present.

7. B. Cows have primary and secondary defenses against bacterial infection. • 1. Primary defenses inhibit the ability of the bacteria to enter the body of the animal. Examples would be the skin or mucus lining of the nasal and throat cavities. • 2. Secondary defenses directly fight the pathogen once it has gained entrance to the body. Examples are antibodies and phagocytes. Antibodiesare protein-like substances that combat and destroy bacteria, while phagocytesare living, sometimes moving, cells that ingest microorganisms or other cells. Phagocytes can be found in the blood, lymph nodes, spleen, and bone marrow to name a few locations.

8. C. The most numerous organisms on Earth are bacteria. A small handful of soil contains billions of bacteria organisms. Bacteria are able to survive and thrive in nearly every habitat because of the adaptations of the metabolic functions. This metabolic adaptation, along with their small size, rapid reproductive rate, and ability to form resistant spores allow them to survive adverse conditions.

10. What are the different clinical levels of mastitis? • A. Peracute—This level of mastitis is characterized by a swollen, hot quarter of the infected udder, a sudden onset of high fever, depression, and anorexia(failure to eat), and a sudden drop in milk production. • B. Subacute—This level is characterized by a warm, swollen quarter along with a decreased appetite and decreased milk production. This level is less obvious than peracute.

11. C. Subclinical—This level has no clinical signs of mastitis, but may show a decreased milk production. The appetite of the cow remains normal during this level. Somatic cell counts in the milk will be the only real indication of an infection. Streptococcus agalactiaeand staphylococcus aureusare both types of bacteria that live in mammary and udder tissues and account for 95% of subclinical cases of mastitis. • D. Chronic—Chronic mastitis is the most severe, usually having a continual inflammation(a protective tissue response caused by the host immune system in response to bacterial infection) of the mastitic quarter of the udder, which usually leads to abscesses of the udder.

13. How do we correctly use the California Mastitis Test (CMT) in the diagnosis of bovine mastitis? • The California Mastitis Test (CMT) is a test used to identify the number of leukocytes, or white blood cells, present in the milk. Since white blood cells are produced to combat infection and disease, the greater the number of leukocytes, the greater the indication of an infection. • A. It is important to only test raw milk with the CMT. Pasteurized milk will not contain any bacteria because of the high heat during pasteurization.

14. B. The CMT is completed by filling each quadrant of the four-quartered paddle with a small amount of raw milk. Reagent is then added to the milk in each quarter and the paddle is gently swirled and tilted to mix the reagent with the milk. Results should appear almost instantly. • C. The degree of mastitis present is directly related to the amount of precipitate or gel that the mixture forms. The greater the gel formation, the more assured the producer can be about the presence of mastitis.

16. What is the economic importance of mastitis to the dairy producer? • A. Any cow showing even slight signs of mastitis must not be allowed to contribute milk to the daily farm bulk tank. Infected milk can and will contaminate any milk that it comes into contact with. • B. If mastitis is not caught early and the cow is not removed from the milking schedule, an entire volume of milk from a farm may be contaminated. If this milk is put on a truck with other milk, it may contaminate an entire truckload, causing serious financial loss to the producer.

17. C. Cows exhibiting signs of mastitis are usually “dried-off,” or discontinued milking for several days while antibiotics are being administered and the infection is being treated. This also causes financial loss to the dairy farmer as they are still feeding, housing, and medicating the infected cow, but not receiving any income from its milk production.

18. D. Contagious mastitis bacteria are commonly spread at milking time through the milking machine. Producers can help to control mastitis by following a few precautions. • 1. Teat dipping with antibiotic solution will help to decrease the amount of bacteria being transferred to the milking machine and other cows. • 2. Back flushing the milking machine will also rid the machine of any bacteria that may have been transferred through the milk. • 3. General cleanliness of the milking parlor and all equipment is always important for good herd health.

20. Review/Summary • How do various bacteria cause mastitis? • What are the different clinical levels of mastitis? • How do we correctly use the California Mastitis Test (CMT) in the diagnosis of bovine mastitis? • What is the economic importance of mastitis to the dairy producer?