Bovine Mastitis

R. W. BROWN, JR.

MASTITIS means inflammation of the udder. It results principally from infection with micro-organisms.

Many kinds of bacteria and some yeasts can produce mastitis. The streptococci (mainly Streptococcus agalactiae, S. dysgalactiae, and S. uberis) and the staphylococci (Micrococcus pyogenes) are the chief causative agents, but mastitis due to the bacteria Escherichia coli, Aerobacter aerogenes, and Pseudomonas aeruginosa has been occurring with greater frequency.

Other organisms, such as Pasteurella multocida, yeasts, and acid-fast bacilli, also have caused outbreaks of mastitis, which have involved a large proportion of the cows in different herds. Another organism that usually causes sporadic cases, particularly in the dry cows rather than in lactating cows, is Corynebacterium pyogenes.

The udder also can become infected with bacteria that cause tuberculosis, brucellosis, and scarlet fever or streptococcic sore throat in man. Most of the varieties of bacteria found in mastitis, however, are harmless to the consumer. When milk is pasteurized properly, practically all danger is eliminated.

The bacteria that cause mastitis are usually carried from diseased cows to the teats. of healthy cows on the hands of milkers or in the teat cups of milking machines during milking. Bacteria also can be spread by flies or by contact with contaminated bedding or floors.

Injury to the teat opening and teat canal and the improper use of teat tubes and dilators also are responsible for some udder infections.

The teat canal is of considerable importance in preventing infection and should be protected from injury as much as possible. Once the bacteria enter the opening in the teat, they may pass up the teat canal and establish themselves in the milk cistern or lower part of the quarter. From that point they spread to other parts of the gland.

MASTITIS EXISTS IN TWO FORMS--acute and chronic.

Acute mastitis is readily detectable and is the form most familiar to the cattle owner. The affected quarter is hot, tense, hard, and tender. Milk secretion is largely or entirely suspended. The milk may be watery, straw-colored, or blood-tinged and may contain few or many clots. A general systemic disturbance, such as depression, fever, and loss of appetite, may be present. In acute mastitis, the organisms have invaded and inflamed much of the involved quarter.

Chronic mastitis is not readily recognized. That is because a general balance exists between the infecting organisms and the udder, with the result that few observable symptoms develop, although damage to the secretory tissue does occur.

Inflammation like that of the acute form also develops in chronic infections of the udder, except that it usually involves only very small areas of secretory tissue at any one time. Consequently the gland is not swollen and the milk appears normal, but the inflammation changes the composition of the milk. The milk does not contain the usual amounts of butterfat or milk sugar, but the number of leucocytes, the salt content, and the products resulting from inflammation and bacterial activity increase. Even those changes will not be found if the areas of inflammation involved are microscopic yet the gland is infected and may be a constant source of infection to other cows.

Sometimes during a chronic infection, flareups occur. They may develop into acute mastitis or they may be milder and cause little or no swelling of the gland, but will change the milk so that it has flakes or clots and a watery or unusual appearance.

The milder symptoms are often called subacute mastitis and may disappear after several milkings, although the quarter remains infected.

As a result of the inflammation, the cells that secrete milk become inactive and may be replaced by nonsecreting fibrous or scar tissue.

When large areas of secretory tissue are destroyed, as in acute mastitis, the quarter becomes atrophied and hard. The changes are gradual in chronic mastitis. The. hard areas, circumscribed or diffuse, usually are formed first near the milk cistern. The quarter gradually loses its soft, pliable quality. In advanced cases it becomes hardened throughout, and the secretory tissue is lost almost entirely.

The change in the character of the udder tissue causes a drop in milk production and shortened lactation periods. How long it takes for the change to occur in chronically infected quarters varies according to the virulence of the invading bacteria, the cow's natural resistance, and the number of acute or subacute attacks. Sometimes the animal passes through several lactation periods before the disease manifests itself, but many cows become useless in a short time.

THE CONTROL OF MASTITIS in any herd in which mastitis has become a problem is best attained by adopting a control program that includes an accurate diagnosis, adequate sanitary and management practices, proper treatment, and close cooperation between the dairyman and veterinarian.

The importance of management and veterinary service in the control of Streptococcus agalactiae mastitis was shown in a study conducted by the New York State Mastitis Control Program. In herds that had good management and adequate veterinary service, 71 percent made good progress in controlling mastitis, but in herds with poor management and inadequate veterinary service, only 19 percent made good progress.

EARLY DETECTION and treatment of infected udders are necessary if one is to control the spread of infection. Acute attacks are diagnosed readily by clinical symptoms, but the chronic form presents some difficulty.

A combination of cultural and microscopic examination of quarter samples of milk is the best way to diagnose chronic udder infections. They are laboratory procedures that require milk samples drawn into sterile tubes or vials and trained persons to run them. All milk samples must be obtained as aseptically as possible. That means that the organisms that occur outside the udder on the skin and in the manure, dust, or bedding must be kept out of the sterile tube as the milk is withdrawn from the teat. Therefore, before the milk samples are obtained, the udder and teats should be washed and the teat openings thoroughly cleaned with a piece of cotton soaked with alcohol or some other nonirritating disinfectant. Any conditions that favor the raising of dust in the barn at the time of sampling should be prevented.

SIMPLER TESTS can be used on the farm. They depend on the physical and chemical changes in milk produced by mastitis. Anybody who uses them should understand that abnormal changes do not appear regularly in the milk of all cows with chronic mastitis and that the type of organism infecting the udder cannot be determined. A positive test in most instances indicates an infected quarter. But a negative test does not indicate that the quarter is not infected.

The simplest test uses the strip cup. Several streams of milk are drawn from a quarter into a cup covered by a fine-mesh wire screen or into a pan with black plastic or metal plates. The appearance of clots and flakes or watery or off-colored milk usually is evidence of mastitis. The test is limited because only infected udders that show gross changes in the milk can be detected. The strip cup should be used before each milking or at least once a day.

The second test is the bromthymolblue test. It is carried out by adding specific amounts of milk and dye solution in a test tube or by drawing a small amount of milk onto blotters impregnated with dye solution. Blotters and kits that contain test tubes, dye solution, and directions possibly may be purchased from farmers' cooperatives, feedstores, drugstores, or mail-order companies that sell farm equipment. The color resulting from the mixture of milk and dye depends on the degree of acidity or alkalinity of the milk. Milk from healthy quarters is slightly acid and gives a yellowish-green shade. In exceptional cases, a bright yellow or acid reaction may be observed. Milk from quarters affected with mastitis is predominantly green, because the milk is more alkaline. The more alkaline the milk, the darker the shade of green becomes. This test discloses a somewhat larger number of diseased animals at any one time than the strip cup, but it should be used primarily to determine the relative amount of mastitis in a herd. The test, under most circumstances, will detect only about 33 to 50 percent of the infected quarters.

Another method for determining abnormal milk is the modified Whiteside test. It is simple and is more accurate than the other tests mentioned. It is used for individual cows. On an experimental basis it has been found useful for testing composite milk samples at a creamery to determine the herds from which mastitis milk is being delivered. To perform the test, 2 drops of a 4-percent solution of sodium hydroxide are added to 5 drops of fresh milk on a glass plate. If the milk has been refrigerated, only one drop of sodium hydroxide is used. The mixture is stirred with a glass rod for 20 seconds and then examined. Normal milk shows little or no change. Abnormal milk shows varying changes from a slight precipitate to a thick, sticky mass.

Neither the bromthymolblue nor Whiteside tests should be used during the first several weeks of lactation or when the cow is almost dry, because false-positive reactions may occur.

VARIOUS MANAGEMENT practices help control mastitis in a herd. Milking procedures and injury to the teats and udder have received the greatest attention as predisposing causes of mastitis, and most control programs emphasize measures to control them.

Because the act of milking provides a constant source of contact between infected and healthy udders, all cows with infected udders should be milked last.

To minimize the spread of disease-producing organisms from cow to cow, separate cloths soaked in a solution of chlorine (250 to 400 parts of chlorine per million parts of water) or quaternary ammonium compounds (a 1: 5000 dilution of the active compound or that recommended by the manufacturer for sterilizing dairy equipment) should be used to wipe the teats and udder of each cow before milking. Between milkings the cloths should be washed, boiled, and dried. The teat cups of the milking machine should be submerged in water and then in a solution of aqua-ternary ammonium compound or chlorine between each cow. The water and disinfectant solution should be changed often.

After the cow is milked, each teat should be immersed in a small amount of the disinfectant solution. That removes from the end of the teat the drop of milk, which tends to attract flies or contaminate the bedding.