What is 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|
|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.
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.
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|
|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|
|Cow||No observable changes|
|Udder||Lumps may be felt|
|Milk||Mild changes, such as wateriness|
|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.
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).
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.
Guides on BMCC levels
|Below 150,00 cells/mL||Excellent mastitis cell count control|
|150,000 to 250,000||Good - below 250,000 is the level for premium payment in most dairy companies; some use 200,000|
|250,000 to 400,000||Moderate mastitis and cell count control|
|Above 400,000||Warning: This milk is not considered fit for human consumption by the European Union and may lead to significant export restrictions.|
Colostrum (sometimes called ‘beastings’) is the thick, yellow, sticky secretion produced by the udder pre-calving. It contains high levels of protein and antibodies to boost calf immunity. The first milking removes the colostrum but the cow makes ‘transition milk’ for up to 8 milkings – and 10 milkings for induced cows. Even though this transition milk may look normal. it must not be put in the vat. Keep cows in a ‘fresh cow mob’ until they have had 8-10 milkings.
Dry Cow Treatment
Antibiotic Dry Cow Treatment (DCT) is injected into the udder immediately after the last milking of a lactation and remains there in concentrations high enough to kill mastitis bacteria for between 20 and 70 days. It can also be useful in curbing new infections early in the dry period, before teat canals seal off.
It may be used in all cows (Blanket Dry Cow Treatment) or only those whose lactation-long cell counts suggest infection susceptibility (Selective Dry Cow Treatment).
Teat sealants provide non-antibiotic protection during the dry period and at calving, but teatseal must be carefully stripped out of each treated teat at the first milking. Failure to completely remove teat seal can lead to residues in milk that cause blemishes in maturing cheese Milk from cows treated with teat seal must not enter the vat for at least 8 milkings.
Decide dry cow mastitis strategy – drying off dates and Dry Cow Treatment (PDF, 107KB)
At the end of lactation, dairy cows require a dry period that is sufficiently long to allow the udder tissue to repair and rejuvenate. This Technote provides information on strategies to consider for Dry Cow Treament.
Guide to choosing an appropriate dry cow treatment strategy (PDF, 23.6KB)
If you are milk recording, proceed down this chart.
Export Slaughter Interval
An Export Slaughter Interval (ESI) is the period following treatment when cattle are unsuitable for processing for some export markets. A list of ESIs for veterinary chemicals can be found on the reverse side of the National Vendor Declaration (NVD) form. More information and sample NVDs can be found at the Meat and Livestock Australia site.
Genetic resistance to mastitis
Most reduction in mastitis comes from improved management, but breeding for increased resistance to mastitis can also have long-term benefits. Genetic variation for Cell Count does exist and some bulls have been found to produce daughters that are more resistant to mastitis than others. Include mastitis resistance in your herd breeding objective by choosing bulls from the Profit or Mastitis Resistance tables in the Good Bulls Guide.
The impact of genetics on mastitis and cell counts (PDF, 76.7KB)
Management is the predominant influencer of mastitis in a herd so genetics isn’t a ‘silver bullet’ to solving a mastitis problem. However, for little or no cost, a dairyfarmer can make a long-term difference to the mastitis resistance of the herd by selecting bulls from the Mastitis Resistance list on the Good Bulls Guide.
Hand-held conductivity meters
Salt leaks into the milk after udder damage, increasing the milk’s electrical conductivity. Hand-held conductivity meters can detect quarters with subclinical infections or very early clinical cases, before the milk changes are visible.
Conductivity levels vary between cows, and at different times during milking so compare between quarters in the same cow at the same time, rather than rely a target conductivity level. A single reading for a cow will not give you a very accurate picture of its udder health; it is better to have a number of readings throughout lactation and it pays to recheck a suspect quarter at the next milking. Do not treat cows based on conductivity results alone
Maximum Residue Limit
The Maximum Residue Limit (MRL) is the maximum allowable concentration of agricultural or veterinary chemicals in milk or meat.
Milk fever (hypocalcaemia) affects mature dairy cows just before, or soon after calving, when there is a sudden drop of blood calcium levels. Cows become weak, may go down, be unable to rise and die if untreated. Injected calcium is a rapid cure in most cases.Milk fever control involves diet manipulation before and at calving to boost calcium levels.
Milk Quality Payment Schemes
Most Australian dairy factories pay more for vat milk with lower Bulk Milk Cell Counts (BMCC). In some states factories will not collect milk above a ceiling BMCC. Total Plate Count levels may also be included in some quality payment schemes.
A lab test to identify milk-borne bacteria, that involves spreading milk on sterile plates covered with growth stimulants, then incubating the plates.
Milk cultures (PDF, 53.9KB)
Factsheet explaining when it is worthwhile culturing milk samples from cows and dealing with cows with high cell counts.
National Vendor Declaration form
Farmers selling cows must complete a National Vendor Declaration (NVD) which documents each animal’s exposure to agricultural and veterinary chemicals. Farmers selling for slaughter or feedlotting have the option to complete an NVD, however many buyers will not buy cattle without one.
A cow’s brain secretes oxytocin in response to her calf sucking, or anticipation of milking. The hormone makes muscle cells contract, which squeeze milk into the milk ducts in a process called milk ‘let-down’.
If cows are anxious or uncomfortable, oxytocin might have to be administered to help milk let-down.. Oxytocin also helps completely remove milk from inflamed udders.
Oxytocin is available as an injectable drug (brand names are: Butocin Oxytocin Injection, Oxytocin Injection, Oxytocin-S and Syntocin). These are only available from your veterinarian.
Rapid Mastitis Test
Rapid Mastitis Test (RMT) detects subclinical mastitis by estimating the cell count of the milk. It does not give a numerical result but scores milk according to the degree of gel reaction response. A small amount of milk from each quarter is squirted into separate dishes, an equal amount of reagent is added and the level of gel reaction estimated. It is a cheap and easy test that can be done during milking, but requires experience to read quickly and efficiently.
Udder oedema (called ‘flag’) is swelling under the udder skin, and sometimes along the belly, in pre-calving cows. It mostly occurs in maiden heifers and can disrupt milking. It is mainly caused by changes in blood flow and restricted fluid drainage. Start milking to reduce the udder volume and the oedema will usually clear.
The withholding period (WHP) is the minimum permitted time between last use of a drug or chemical and sale of an animal product for human consumption. The exception is the milk WHP after Dry Cow Treatment which is the time post-calving and after the specified minimum dry period.
Cows culled from our dairy herds must not have any treatment residue above its Minimum Residue Limit (MRL) when they are sold for slaughter. Errors have the potential to jeopardise Australia’s cattle meat export trade, which is worth $2.6 billion a year.
To avoid errors all cows treated with antibiotic (by injection or intramammary infusion, etc) must be identified. Dairy farmers tend to use markings that are easily seen during the withholding period for milk but not for the full length of the withholding period for meat. Identification of animals for the duration of the meat withholding period requires permanent identification and written records that can be referred to when determining whether withholding periods for meat have expired.
Cattle are unsuitable for processing for some export markets for a specified period after treatment. The length of time is referred to as the Export Slaughter Interval and more detailed information is available from the Australian Quarantine and Inspection Service.
The Export Slaughter Interval is not stated on the label of antibiotics as it varies between countries and alters regularly with changes in the requirements of importing countries.