Mastitis in Cows – Causes, Detection and Treatment

The detection and treatment of mastitis in cows is critical for managing milk quality and herd health, and maximising production. Cow mastitis detection and treatment will help you optimise your milk quality and pay out, and reduce antibiotic treatment and culling costs.

What is Mastitis?

Mastitis is a potentially fatal inflammation of the cow’s mammary gland, which is usually caused by bacteria entering the teat canal and moving into the udder tissue. Toxins released by mastitis bacteria damage milk-secreting tissue and ducts throughout the mammary gland, reducing milk yield and quality. Mastitis can occur at any stage of lactation, including the dry period, but is most likely in the first month after calving and in late lactation.

What Causes Mastitis in Cows?

Mastitis occurs when large numbers of white blood cells (leukocytes) migrate into the mammary gland, usually in response to bacteria invading the teat canal through environmental contact or during the milking process. It can also be caused by an injury to the cow’s udder.

How Does Mastitis Affect Milk Production?

Mastitis can be associated with a fall in milk yield. This can be a result of incomplete milking of the infected quarter(s) due to discomfort or blockages, or damage to milk secreting tissue caused by the infection. The reduction in yield may be temporary or permanent.

The Importance of Early Detection of Mastitis in Cows

Early detection of mastitis in cows enables you to limit the spread of infection within your herd, minimise the impact on your bulk milk quality, and improve treatment success. Undetected mastitis infections can spread between quarters and cows through milking machines and udder handling by staff. Infected cows that are not detected or don’t receive the appropriate treatment can develop chronic long-term infections that lower production, and increase the risk of lower sale values and culling. It only takes a few infected animals to lower your milk quality by increasing the bulk milk somatic cell count, especially during calving or in late lactation when fewer cows are contributing to the vat, or if you have a small herd. A high bulk milk somatic cell count can lead to penalties from your dairy company and a lower pay out.

Mastitis Control and Milk Quality Targets

The generally-quoted aims for mastitis control and milk quality on UK dairy farms are:

A clinical mastitis incidence rate of no more than 30 cases per 100 cows each year.
A mastitis persistence rate of no more than 20% of the herd affected each year.
A mastitis re-occurrence rate of less than 10% of the total number of cases.
A herd-average somatic cell count less than 150,000 cells per millilitre of milk.
An average Bactoscan result of less than 5,000.

Mastitis in Cows Response and Treatment

Farmers are encouraged to get a vet involved at the first sign of rising somatic cell counts so the infected cows can be quickly identified, and separated from the main herd. This will help prevent the infection from spreading to other cows, minimise the impact on milk quality, and provide some time to find the underlying cause of infection. If mastitis is identified in your herd at levels worse than the industry targets above, it is recommended that you work out a suitable response plan in consultation with your vet.

Sub-Clinical versus Clinical Mastitis

Mastitis can be characterised as clinical or subclinical. Clinical mastitis is defined as inflammation of a mammary gland that can be easily detected through a visual examination of the milk and/or udder. Subclinical mastitis is defined as the presence of inflammation with a normal appearing mammary gland and visibly normal milk, which usually has an elevated milk somatic cell count.

Signs of Clinical Mastitis in Cows

The diagnosis of clinical mastitis is normally based on the detection of abnormalities in a cow’s milk or udder. The common abnormalities that signify clinical mastitis include milk that contains clots or is discoloured, watery or flaky. The amount of swelling, severity of pain and appearance of the cow will indicate the severity of infection. Signs of clinical mastitis in the udder are swelling, heat, hardness, redness or pain. Other common signs of infection include reduced milk production, elevated body temperature, lack of appetite, and reduced mobility. As a general guide:

Mild clinical mastitis is signified by abnormal milk, usually indicated by clots, flakes, and/or changes in the colour and consistency of the milk secretion.
Moderate clinical mastitis is signified by abnormal milk and mammary gland, indicated by inflammatory changes in the tissue such as redness, heat, pain, and swelling.
Severe clinical mastitis is signified by abnormal milk and mammary gland, and a noticeably sick cow. This is usually indicated through elevated body temperature and reduced rumination, appetite, hydration, and an overall distressed demeanour.

Fore-Stripping

Fore-stripping (also known as foremilk stripping) is an effective way to detect clinical mastitis. It is carried out by hand milking a few squirts onto a suitable dark surface. This will allow any signs of infection to be spotted, such as discolouration, clots, flakes, stringiness or watery secretions. Fore-stripping will also help highlight any abnormalities of the teats or udder, allowing cows to be prioritised for further evaluation or treatment. Milk should never be stripped into a milker’s hand due to the high risk of spreading bacteria from cow to cow. Because fore-stripping is time-consuming and labour intensive, some farmers choose to only strip one or two teats per cow per milking. It is generally recommended that farmers consider fore-stripping all cows in their first month of lactation and during periods of high risk, such as calving or when a high bulk milk somatic cell count indicates the presence of infections within the herd.

Detecting Sub-Clinical Mastitis in Cows

Sub-clinical mastitis is the most common and challenging to diagnose due to the lack of visible symptoms. Three common ways to detect it are the California Mastitis Test, measuring milk electrical conductivity and somatic cell counts.

California Mastitis Test

The California Mastitis Test (CMT) is a simple manual cow-side screening test that detects subclinical mastitis in individual quarters. CMT works by disrupting the cell membrane of any somatic cells present in the milk sample, causing the DNA in those cells to react with the test reagent, forming a gel. The most common test reagents used are domestic detergents or a purpose-designed `CMT-Test’ reagent. Testing is carried out by squirting a small amount of milk from each quarter into a dish at milking and adding an equal amount of reagent. The solution is then gently agitated to mix it. After mixing, the amount of gel formation is visually assessed to determine if a high somatic cell count is present. The gel is scored on a scale of zero (with no change) to three (where the mixture turns into an almost solid gel). A score of two or three is considered a positive indication of mastitis. The gel formation caused by a level two reaction can sometimes appear as traces of slime that can be difficult to detect in some samples.

Electrical Conductivity Tests

The electrical conductivity of milk increases when a cow has mastitis due to the infection causing sodium and chloride ions to leak into the milk from the blood. Conductivity testing can be carried out cow-side in the parlour using hand-held, portable instruments or by using in-line sensors connected to the milking machine. An infection is generally deemed present when the conductivity reading for one of the cow’s quarters is more than 15% higher than its lowest quarter reading. The accuracy of conductivity meters can vary due to the type of pathogen causing the mastitis and the amount of tissue damage. Milk conductivity can also be affected by other non-mastitis related factors, such as temperature, suckling calves and milk fat content. Due to the lack of sensitivity, conductivity testing is generally not considered to be a reliable indicator of mastitis on its own. It is recommended that animal’s with high electrical conductivity readings have further evaluation before treatment decisions are made.

Somatic Cell Count Measurement

Measuring somatic cell counts (SCC) is one of the best ways to detect sub-clinical mastitis. Somatic cells are mainly made up of white blood cells called leukocytes, which increase in response to the bacteria that cause mastitis. SCC is quantified as the number of somatic cells per millilitre of milk. The higher the SCC, the worse the infection is deemed to be. Regular SCC checks will allow you to quickly identify infected animals and take action to protect your herd health and milk quality. SCC measurement is usually carried out in a laboratory using sophisticated instruments as part of a farm’s standard herd testing regime at intervals of four weeks or more. Automated SCC sensors are available for use in the parlour, as part of your regular milking routine. The frequent testing and real-time up-to-date data they provide gives a more complete picture of mastitis in your herd over time and will allow you to detect infections much earlier and take action if needed, without having to strip the whole herd.

Saber SCC Automated Milk Sensor

Saber SCC automated milk sensors provide quick and accurate real time somatic cell count data for individual animals within minutes of cupping. A standard installation comprises sensors at one in every four milking points, providing weekly up-to-date data for almost the entire herd and approximately 150 tests per lactation for every cow. Saber SCC automatically tests 1 millilitre of milk during milking and determines the SCC result straight away. The results and any alerts from the sensors can be viewed on your device of choice to help you make real-time herd decisions and better manage mastitis and bulk SCC levels.

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