Mastitis - The Disease, Its Transmission and Prevention

What is Mastitis?

Mastitis, or inflammation of the mammary gland, is the most common and the most expensive disease of dairy cattle 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 control and prevention of diseases and ailments in dairy herds mean more to the success of a well-bred dairy herd than any other single factor. As the herd increases in number and the individuals in the herd improve in production, diseases occur more frequently. This is only natural. With larger numbers more animals contact each other, increasing the possibility of infection. High-producing animals are highly developed and therefore hard working. They cannot withstand the hardships and contagion of disease as can the "border cow," which is largely on a maintenance basis.

Prevalence of Mastitis

Mastitis is found in small herds of dairy cows as well as in large herds. If all milking herds were checked by means known to detect mastitis, it is doubtful that any herd of any size would be entirely negative for all of the tests. Some researchers have estimated that one or more milking cows in nine of ten dairy herds would react positively to at least one of the tests. This positive reaction does not necessarily mean that the cows show evidence of active mastitis. But it does mean that there is a danger of mastitis under inducing conditions, such as bruised udder and lowered resistance. In some herds in which no control measures are practiced, it is not uncommon to find mastitis in 50 to 75 percent of the cows. It is likely to spread further unless control measures are taken.

Does Mastitis Decrease the Milk Flow?

Mastitis takes a heavy toll on the profits of the dairyman. Milk production of cows infected with this disease may decrease by 20 to 30 percent on average. Heavy-producing cows having mastitis have been known to drop from an average production of 95 pounds of milk a day to 30 pounds. That is not all. Many cows permanently lose the function of one or more quarters of the udder. Statistics show that about 40 percent of all milk cows marketed in the United States are sold because of defective udders. In addition to these losses, infected cows need extra attention when they are milked, thus adding to the work of the dairyman. Mastitis is a disease that should be eliminated from every dairy herd. Management practices should be taken to keep it out.

What is the Real Cause of Mastitis?

Mastitis is an inflammation of the udder caused by bacteria (germs). The bacteria are found in barns, in materials kept in barns, and in the hands of milkers. They are also on milking machines, particularly on the rubber parts which are allowed to become dirty. When these rubber parts have been used for some time, they frequently have tiny cracks that cannot readily be seen with the naked eye but are visible under the microscope. These cracks harbor millions of bacteria. Unless the rubber is carefully and thoroughly cleaned, it is an important source of contamination. The germs enter the udder through the teat canal or cuts, abrasions, or other injuries to the udder. Because the udder of a dairy cow is such a sensitive organ, as well as because germs can enter it through bruises, every precaution should be taken not to injure it. The following practices should be followed to avoid injuring the udder.

What to Do

l. Handle the udder gently.

2. Leave the milking machine on only until the cow has been milked dry, not after she is dry.

3. Follow the manufacturers' directions for operating the milking machine. Do not increase the vacuum of a milking machine above what the manufacturers recommend.

4. Be sure that the udder is not injured by being kicked, bunted, or. stepped upon by other cows.

5. Drive cows on a walk. Faster driving causes the udder to swing.

6. Provide enough bedding, otherwise the cows are forced to lie on cold rough floors where the udder is exposed to sharp gutter edges.

7. Use teat tubes, teat dilators, and teat plugs only as a last resort. Drying up an infected quarter is preferable.

8. Milk cows regularly.

9. Be careful when drying off cows.

10. Keep milking machines clean and have good inflations.

Considerable experimental work on mastitis has been done by the international research institutes. It has been established that most of the cases of mastitis show Streptococcus agalactiae. Occasionally staphylococci are found. When either of these organisms is found in the milk of any quarter or a large number of leucocytes are found, the presumption is that streptococci or staphylococci were the cause of the mastitis condition. Only a trained bacteriologist understands how to prepare the milk so that these organisms can be seen under a microscope. It also requires a trained technician to identify the organisms. Practical feeders frequently attribute mastitis to heavy feeding, particularly of high-protein feeds. However, no experimental data are available to show that feeds of any kind cause mastitis. Feeding trials in which cottonseed meal was fed in liberal amounts did not indicate that this high-protein feed induced mastitis. It cannot be said that overfeeding cows with concentrates does not result in trouble. When cows are over-fed on concentrates and go off feed, their resistance is lowered and they may contract any disease. If cows are exposed to heavy infections of mastitis while in this condition, they may come down with an attack of mastitis.

Symptoms and How to Detect Mastitis

The milker must recognize mastitis in its early stages, because if the cow is to be cured or the disease controlled, action must be taken as soon as possible after the infection is

Clinical Mastitis — visible signs of mastitis, which include: Mild signs — flakes or clots in the milk, may have slight swelling of the infected quarter. Severe signs — secretion abnormal; hot, swollen quarter or udder; cow may have a fever, rapid pulse, loss of appetite, dehydration, and depression; death may occur.

Subclinical Mastitis — no visible signs of the disease: The somatic cell count (SCC) of the milk will be elevated. Bacteriological culturing of milk will detect bacteria in the milk. Clinical mastitis causes the greatest financial loss to dairy farmers through lowered milk production For every clinical case of mastitis, 15 to 40 subclinical cases will occur.

Somatic Cell Count (SCC) — the number of leukocytes or white blood cells per milliliter of milk. Normal milk will have less than 200,000 cells per milliliter. An elevated SCC is an indication of inflammation in the udder. The bulk tank SCC indicates the level of subclinical mastitis and the loss of milk production in a herd due to mastitis.

When the properly incubated and stained milk samples are examined under the microscope and long-chain streptococci organisms are found, infection is present in the udder. In much of the experimental work that is being done on mastitis, a positive microscopic test is the best evidence that the cow has mastitis.

How Mastitis Spreads

The spread of infectious mastitis is largely by specific bacteria. Various types of bacteria are responsible for mastitis but many research workers have found that 90 percent of mastitis cases are caused by Streptococcus agalactiae. When these bacteria are present in the udder, they are given off in the milk. Then they can be found on the milker's hands, the teat cups, and dairy utensils. If the milk from the cows having mastitis is milked into the bedding or the gutter, the dust in the barn air becomes laden with mastitis bacteria. Flies may carry the bacteria from the teats of one cow to another and thus spread the infection.

The bacteria enter the healthy udder through the teat canal. The sphincter muscles ( circular muscles at the end of the teat) are more relaxed during and right after milking, therefore there is more likelihood of the bacteria entering the udder during or soon after the milking process.

Many milking cows and virgin heifers have the bacteria in the udder. All that is necessary to bring on mastitis is some inducing factor, such as bruising, butting or otherwise injuring the mammary tissue, or even lowering the vitality or disease-resisting ability of cows. Cows that have recently freshened or have had attacks of diseases and therefore have a lower resistance, may suddenly have an attack of mastitis. Cows that become chilled when they drink cold water or are exposed to cold winds or inclement weather, may also have an attack of mastitis.

Prevention and Control

"An ounce of prevention is worth a pound of cure" is even more applicable in the case of mastitis than most other diseases, because the disease attacks the udder, a highly sensitive organ, and is very difficult to cure when it can be cured at all. Therefore, the dairyman should be exceedingly careful in managing to prevent mastitis from entering the herd.

• Keep cows comfortable. No successful dairyman will permit his cows to be milked or handled in such a manner that they are injured in any way. Every precaution should be taken to make the cows comfortable. Feed them and care for them so that they can resist slight infections. A cow's physical condition should be watched so carefullv that as soon as she is ailing she will be cared for. If she needs the services of a veterinarian, call one immediately. If she needs home treatment, see that she gets it.
• Keep barns clean. Sanitation is highly important in the management of a dairy herd. A slovenly, untidy barn is no place to produce a food as precious as milk. Sanitation not only means a superior product but goes a long way in keeping the herd healthy enough to ward off minor infection. Cleanliness of milking machines, barns, dairy utensils, and the milkers and others who handle the milk should be beyond question.
• Milkers should be healthy. The organisms which produce septic sore throat in human beings can grow in the udder of cows and cannot be distinguished from the Streptococcus agalactiae under the microscope. Therefore, no one with sore throat or any other communicable disease should be permitted to milk cows or handle the milk. It should always be kept in mind that milk is a very good medium for growth of all bacteria. Therefore every precaution should be observed to prevent contamination.

Good Milking Practices

Gentleness in milking and handling the cows is important. A rough hand-milker or one who does not understand the operation of a mechanical milker will frequently bring on mastitis. Once it is in the herd, the same type of person will cause mastitis to spread. Careless milking and herd management are probably the greatest factors contributing to the occurrence and spread of mastitis in dairy herds.

The cow should be comfortable and entirely at ease when she is being milked. Anything that might scare her or cause her to become nervous and excited when being milked must be avoided. Avoid injury to the cow's teats and udder.

If a teat has been stepped on or otherwise injured, the use of a milking tube to get the milk from the injured quarter usually re- 10 South Dakota Exp1wi1nent Station Circular 54 results in infection. Chances are that better results will be had by not using the tube. Keep the teat clean with a disinfectant wash and allow the quarter to dry up. It is extremely difficult to use a milking tube under barn conditions and not introduce infection. Infecting a quarter by using a milking tube usually results in the loss of the quarter. It may even result in generalized infection and the loss of the cow.

The udder of a cow should be prepared for milking and then the cow should be milked as rapidly as possible. The teats and udder should be washed with a warm chlorine solution (250 parts per million) before milking. This practice not only prepares the cow to let down her milk but also washes away and destroys any bacteria that may be on the teat. After the cow has been milked, a good practice is to dip the teats in a shallow pan or cup of chlorine solution containing 250 parts per million of available chlorine. This practice will destroy any bacteria that may be left on the teats and later enter the teat canal.

The teat-cups on the milking machine should be dipped into a chlorine solution after milking each cow to avoid carrying bacteria from one cow to the next. In hand milking the milker should <l wash his hands for the same reason. These practices take time and are often inconvenient to perform, but they are important factors in maintaining the health of the herd and in controlling mastitis.

Cows that have lost one or more quarters and whose udders indicate considerable scar tissue should be slaughtered. There is little chance of curing such cows and they may be a source of spreading the infection to other cows in the herd. Cows having considerable scar tissue in their udders are not likely to be profitable producers.

Infected cows that are to be retained in the herd should be isolated from the balance of the milking herd. If it is impossible to house such cows in a separate barn, they can be placed in one section of the barn and milked last to avoid spreading the infection to uninfected cows.

Milk From Mastitis Cows

No data are available to indicate that the organism in mastitis, Streptococcus agalactiae, is pathogenic (disease-producing) to man. However, a heavy infection might prove serious. Feeding mastitis-infected milk to calves is not recommended. In many cases of clinical mastitis, the milk is so abnormal in appearance and odor that no one would want to use it for any purpose. Although the milk from an infected quarter cannot be used safely, milk from the other quarters of the udder is normal and can be used. Where the milk cannot be tested for mastitis and it appears abnormal in color or has flakes or chunks of curd in it, it should not be used for human consumption.

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