Mastitis

Mastitis is inflammation of the cow’s mammary gland usually caused by bacteria entering the teat canal and moving to the udder. The main types are:
• contagious mastitis
• environmental mastitis

Cow-associated (or contagious mastitis)

The main bacteria causing contagious mastitis are Staph aureus and Strep agalactiae. They mostly live inside udders or on teat skin and are spread either by splashes of infected milk or sprays during stripping, on milkers’ hands or teatcup liners, and by cross flow of milk between teatcups.
Strep agalactiae bacteria tend to locate in duct areas of the udder where antibiotics are effective. Strep agalactiae are very sensitive to penicillin, so there are relatively high cure rates. However, Staph aureus form pockets of infection protected from antibiotics by scar tissue. A third organism, Strep uberis is sometimes spread at milking.

Habitat		Inside udders or on teat skin
How it spreads		Contamination from infected milk
When it spreads		Milking time
Bacteria		Staph aureus Strep agalactiae
Comments		Staph aureus are a major cause of mastitis in Australia. They are difficult to cure, especially during lactation, so prevention is essential. Strep agalactiae are very sensitive to penicillin, so treatment has a relatively high cure rate.

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Environmental Mastitis

Soil, manure, bedding, calving pads and water host bacteria that cause environmental mastitis. They also occur on parts of the cow other than the mammary gland. Housed cows tend to be more at risk than grazing cows.
The main bacteria are Strep uberis which can sometimes persist, and can spread at milking. The other culprit is E. coli which does not thrive in the lactating udder and often the infections do not persist.
Transition and post-calving cows are very susceptible to these infections because their natural defences are low. Large infections of environmental mastitis bacteria can contaminate teats, especially if udders are wet and exposed to mud and manure, such as when animals lie down during calving.

Habitat	The cow's environment, eg. manure, soil.
How it spreads	Contamination from infected environment; can be introduced with intramammary tubes if teat ends are not sterile when treatment occurs.
When it spreads	Mainly at drying-off and around calving time; most cases seen at calving or early lactation.
Bacteria	Strep uberis, E.coli, coliforms, Pseudomonas. Many others occur occasionally.
Comments	Often causes very severe or acute clinical mastitis. Strep uberis usually responds to treatment, but can be difficult to cure. Coliforms do much of their damage through toxins released after the bacteria die. Antibiotics may not be needed. Do not usually persist in lactating udders. Pseudomonas are virtually impossible to treat and cows that survive must be culled.

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What are the forms of mastitis?

Most cases of environmental mastitis are clinical but subclinical cases occur too. Cases of mastitis caused by Staph aureus can be seen in all the various forms.
Strep agalactiae do not produce black (gangrenous) mastitis but it can occur in all the other forms.

Severe clinical mastitis
Cow	Extremely ill and depressed, may die
Udder	May become gangrenous (black mastitis)
Milk	May initially look normal although the cow is obviously sick, but soon becomes abnormal
Acute clinical mastitis
Cow	May or may not be sick
Udder	Hot, swollen and painful
Milk	Abnormal and can be discoloured and contains cots and/or blood
Clinical mastitis
Cow	No observable changes
Udder	Shows little change
Milk	Abnormalities are seen
Mild clinical mastitis
Cow	No observable changes
Udder	Shows no abnormalities
Milk	A few clots or flakes occur
Chronic mastitis
Cow	No observable changes
Udder	Lumps may be felt
Milk	Mild changes, such as wateriness
Subclinical mastitis
Cow	No observable changes
Udder	No observable changes
Milk	No observable changes but significant changes in milk composition

Why is mastitis control important?

Cows should be kept comfortable and in good health. Farmers will also enjoy higher financial gain from increased production, higher payment for quality milk and reduced costs of treatment and culling. Less mastitis means less risk of antibiotic contamination of milk or meat products. It means more secure domestic and international markets.

More information

What's mastitis control worth to you? (PDF, 32KB)
This article discusses how the Countdown Downunder team has developed an economic model of Australian farms, showing the net gains from lowering the annual average Bulk Milk Cell Count (BMCC).

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Cells in milk

When bacteria enter the udder, the cow sends large numbers of white blood cells to surround and destroy the infection. A small number of udder tissue cells are also shed into milk. Body cells are sometimes called somatic cells (somatic means ‘body’) and their number stays stable after the milk leaves the cow, regardless of filtration or cooling.
The concentration of all body cells in milk is called its Individual Cow Cell Count (ICCC) or Somatic Cell Count (SCC). A sample of milk taken from all four quarters shows the concentration of cow body cells. The sample is usually taken at herd testing.
The concentration of cells varies throughout a milking, so the sample tested should be collected throughout the milking.
Concentrations also vary between morning and evening milkings, especially with unequal milking intervals. Evening milkings have higher cell counts.
The ICCC indicates the likelihood of subclinical mastitis. Uninfected cows generally have ICCC levels of below 150,000 cells/mL. If a cow has had any ICCC above 250,000 during a lactation (a peak of 250,000 or more) she is likely to still be infected at drying-off and require Dry Cow Treatment.
Different infecting bacteria can cause different ICCC patterns. With subclinical cases of Staph aureus cell counts can rise and fall, showing an irregular pattern during lactation while ICCCs in cows with Strep agalactiae can be extremely high. Strep agalactiae infections are easier to treat than Staph aureus; so higher cell counts do not always mean hard-to–treat. cows.
High ICCC levels not associated with infection can occur for up to 20 days post-calving.
Stress can lift ICCC levels in cows. Elevated ICCC levels can also occur in late lactation when milk volume is low and cells are more concentrated. Cows producing less than 5 L/day are likely to have abnormal milk composition, including elevated cell count.
The concentration of cow body cells in vat milk is called a Bulk Milk Cell Count (BMCC), and is an indirect measure of subclinical mastitis in the whole herd.
As an approximate guide, each 100,000 cells/mL indicates about 10% of cows are infected. Vat samples for BMCC should be collected via the drip sample which is taken when the vat is being emptied. This ensures that the milk sample is well mixed.
A series of BMCCs should be assessed to see both the level and the trend for a herd. In herds with BMCCs below 200,000, a sudden increase (of 10% or more) can indicate a clinical case has been missed.