Mastitis in Dairy Cows: Causes, Symptoms, and Strategies for Prevention
Bovine mastitis is the most widespread and costly disease affecting dairy cattle worldwide. It is an inflammation of the mammary gland, typically caused by infection, and can severely impact milk production and quality [1].
What is Mastitis?
Mastitis is an inflammation of the mammary gland, often resulting from microbial infections or physical trauma. The condition can manifest in clinical or subclinical forms.
Clinical mastitis is the more noticeable form, characterized by sudden onset, visible symptoms, and changes in milk appearance. Clinical mastitis is typically easy to detect and diagnose [1].
On the other hand, subclinical mastitis has no obvious symptoms but leads to decreased milk production and quality. Subclinical mastitis is more common and has a greater impact on older animals. Due to the lack of visible symptoms, diagnosing subclinical mastitis is a challenge for dairy farmers and veterinarians [1]. Mastitis is extremely difficult to control, with approximately 20–30% of dairy cows diagnosed at least once during lactation [2].
Negative Implications of Mastitis
Economic loss
In the US, the total failure cost of bovine mastitis averages $72 USD per cow annually. With 8.734 million lactating dairy cows in the US, the estimated total cost of mastitis is $629 million per year. Since this figure only accounts for clinical mastitis, the total annual cost of mastitis, including all cases, could be as high as $1 billion [3]. Similar estimates have been made in other countries, with global annual losses estimated to be around $32 billion, highlighting the importance of strategies to prevent mastitis [2].
Spread of zoonotic pathogens
Milk from cows with mastitis may contain foodborne pathogens. Although pasteurization typically eliminates these pathogens in milk, they can still be an issue in raw milk or cheeses. Additionally, pathogens can produce toxins that persist even after heat treatment, and milk from cows with clinical mastitis may contain antibiotic residues [2].
Symptoms of Mastitis
The symptoms of mastitis vary depending on the severity and type of infection:
Clinical Mastitis
The udder may be swollen, red, and hot to the touch.
Milk can appear watery, contain flakes or clots, or have a yellowish color.
Cows may show signs of pain, such as kicking during milking or reluctance to be milked.
Systemic effects, such as fever and decreased appetite.
Signs of diarrhea and dehydration.
Severe cases of clinical mastitis can be fatal [4].
Subclinical Mastitis
Reduced milk production.
Elevated somatic cell count (SCC), detected through laboratory testing.
Subtle changes in milk composition that may affect taste and processing qualities [4].
Causes of Mastitis
Mastitis is caused by a wide range of pathogens and can be epidemiologically classified into contagious and environmental types [5].
Contagious mastitis
Contagious mastitis spreads from cow-to-cow, particularly during milking. Pathogens such as Staphylococcus aureus, Streptococcus agalactiae, and Mycoplasma spp. reside on the cow’s udder and teat skin, eventually spreading to the teat canal and causing inflammation. These pathogens are most often responsible for subclinical infections [5].
Staphylococcus aureus is the most common cause of clinical and sub-clinical mastitis in dairy cows. This bacteria primarily resides in the udder of infected cows; thus, maintaining good udder hygiene and proper milking practices can help prevent the spread of infection. Staph. aureus triggers a weak immune response, often resulting in chronic mastitis that lasts for several months. While it doesn't usually cause severe illness or death, Staph. aureus produces enzymes and toxins that can permanently damage milk-producing tissues, reducing milk output [5].
Streptococcus agalactiae can be found in the cow's digestive tract and the environment. It spreads through milking equipment, as well as the oro-fecal route through contaminated drinking water. Strep. agalactiae typically causes sub-clinical mastitis and can persist in the mammary glands by forming biofilms, which enhance its resistance to the cow's immune defenses and other stresses [5].
Mycoplasma spp. causes a less common but highly severe form of mastitis. This type of infection leads to significant tissue damage, including fibrosis and abscesses in the mammary glands and lymph nodes. Mycoplasma mastitis outbreaks are sporadic and difficult to control, as these bacteria form biofilms and do not respond to antibiotic treatment. The best control measures are regular monitoring and the quick isolation or culling of infected cows to prevent the spread of infection [5].
Environmental mastitis
In contrast, environmental mastitis is caused by pathogens that reside within the cow's living environment, such as in the bedding and housing of the herd. Opportunistic pathogens, including E. coli, Klebsiella spp., and Streptococcus uberis, can enter the teat during milking due to liner slippage or when the cow's natural immunity is compromised. These pathogens invade and multiply in the cow’s udder, trigger an immune response, and are rapidly eliminated, typically resulting in short-lived clinical infections [5].
E. coli is the most common bacteria found in the environment, especially during wet conditions. It invades the udder through the teat and triggers an inflammatory response. It typically causes a clinical and transient infection, with symptoms ranging from mild (red and swollen udder) to severe (fever and systemic illness). Severe infections can cause irreversible damage to the udder tissue, leading to complete loss of milk production and sometimes death [5].
Klebsiella spp. is found in manure, contaminating drinking water, feed, other cows, and bedding if cattle and environmental hygiene are not well-maintained. When one cow is infected, Klebsiella can contaminate the milking unit and transmit the infection to the next cow that is milked. Klebsiella invades deep into the udder's secretory tissue, compromising its ability to produce milk. As a result, many Klebsiella infections become chronic, causing long-term reductions in milk production for the affected cows [6].
Streptococcus uberis causes recurrent mastitis, associated with both clinical and subclinical infections. It forms biofilms in response to milk components, helping it survive environmental stress and resist antibiotics. Strep. uberis can be found in various parts of the cow, including the udder, skin, respiratory tract, digestive tract, feces, and wounds [5].
Risk Factors for Mastitis
Breeding and Genetics
Genetic factors and breeding practices play a significant role in a cow's susceptibility to mastitis. High-yielding breeds like Holstein-Friesians are more prone to mastitis compared to medium-yield breeds. For instance, Jersey cows and Rendena cattle from northeastern Italy, which produce less milk, are more resistant to diseases, including mastitis. Additionally, cows that have had multiple calves are more susceptible to udder infections than first-time calving cows because their immune systems are weaker [5].
Udder Structure
Udder structure also affects infection susceptibility. Cattle with large funnel-shaped teats, pendulous (low-hanging) udders, or blind quarters after calving are at higher risk for subclinical mastitis. Additionally, teat size and the distance from the teat to the floor can reduce the effectiveness of white blood cells in milk, increasing the chances of udder infections [5].
Age
Older cows are more susceptible to mastitis, likely due to wider or permanently partially open teat canals from frequent milking. Furthermore, the mammary tissue of older cows has increased permeability, mainly due to irreversible damage from previous inflammations [5].
Transition Period
The transition period, defined as the three weeks before and after giving birth, is a high-risk time for diseases like mastitis. Infections are more common at parturition and during the first month of lactation due to immunosuppression caused by increased oxidative stress and low antioxidant defenses [5].
Nutritional Stress and Immune System
During lactation, cows need more energy and nutrients for colostrum and milk production. If their diet doesn't meet these demands, they can experience a negative energy balance. This imbalance, along with deficiencies in trace elements (like selenium, iron, copper, zinc, cobalt, and chromium), amino acids (like lysine and L-histidine), and vitamins (like A, C, E, β-carotene, and lycopene), leads to weakened immune systems and higher susceptibility to infections. Proper diet management during the transition period, including supplementation with vitamin E and zinc, is crucial for preventing mastitis and supporting healthy lactation [5].
Environmental Factors
Environmental conditions and herd management practices play a crucial role in animal health and welfare. Factors such as overcrowding, dirty floors, damp bedding, poor ventilation, and hot and humid climates can create ideal conditions for mastitis pathogens to thrive. These conditions increase the cows' exposure to these pathogens, leading to a higher incidence of mastitis [5].
Diagnosis of Mastitis
Foremilking
Foremilking involves removing the first three to five streams of milk and examining it for signs of clinical mastitis [7]. When milk is stripped onto a dark surface, clots, flecks, or alterations in color or consistency can be easily observed. Changes in milk appearance are often the first signs of mastitis, making foremilking the most effective method of diagnosis. Clots and flakes are more common in mastitis caused by Staphylococcus and Streptococcus, while straw-colored milk is typically associated with E. coli [8].
Foremilking is straightforward and requires no specialized equipment, making it simple and accessible to all dairy farmers. However, time is a major barrier to performing foremilking, as it can be inconvenient to conduct this additional test. As a result, less than 10% of dairy farmers include foremilking in their milking routine [8].
Visual examination
Before attaching the milking clusters, dairy farmers should visually examine and palpate the udder to look for signs of mastitis, including swelling, reddening, hardness, or heat. A quick inspection can detect these symptoms and prevent the spread of bacteria to milking equipment. However, udder changes typically occur in the later stages of mastitis, making udder examination a poor first line of detection. Later identification also means delayed treatment, which tends to be less effective and increases the risk of disease spread [8].
In-line filters
In-line filters within a milking plant can catch clots in the milk, which can be useful for mastitis detection if they are checked after every cow is milked. However, in direct-to-line parlours, the milk would have already reached the main tank before a potential case of mastitis is identified, reducing the filters’ utility as an early detection system. Furthermore, in-line filters can restrict milk and air flow through the tube, reducing milking machine efficiency [8].
Somatic cell count (SCC) concentration
Monitoring the concentration of somatic cell count (SCC) in milk is a common method to detect subclinical mastitis. During the infection, SCC levels increase dramatically due to the influx of white blood cells; SCC levels above 200,000 cells/mL of milk indicate inflammation. SCC can be measured in the lab using microscopy, which is time-consuming and requires specialized equipment and skilled personnel. Alternatively, cell counters use imaging, Coulter counting, or flow cytometry techniques to provide faster and easier measurements [2].
Detection of Mastitis Pathogens
Detecting the pathogen responsible for each mastitis case is crucial for effective treatment and management. Although the tests outlined above indicate disease, they cannot identify the specific pathogen, which is necessary for choosing the right antibiotics and preventing the spread of infection.
Culture-based methods
The gold standard for identifying mastitis pathogens involves culturing milk samples. This process involves incubating milk on culture plates for at least 18 hours to allow bacteria to grow, then analyzing the resulting colonies to identify the pathogen. This method is reliable and cost-effective but requires sterile conditions, can take up to 48 hours, and has a high rate of false negatives (20-50%) [2].
Molecular methods
Molecular diagnostic methods like polymerase chain reaction (PCR) provide higher test sensitivity and specificity than culture-based methods. PCR is also capable of detecting non-viable bacteria, providing a more accurate picture of a potential mastitis infection. Although results are typically available within a few hours, PCR tests are often done in central labs, which can delay result delivery [2].
Recent advancements in field-deployable quantitative PCR (qPCR) technology are promising for real-time pathogen detection in milk. Kraken Sense is developing devices that could be integrated into milk processing plants, offering rapid, on-site testing and allowing for immediate detection and identification of mastitis pathogens in milk. This real-time capability enhances the ability to manage and control mastitis more effectively by providing timely information for decision-making and reducing the lag time associated with central lab testing [9].
Treatment of Mastitis
Mastitis is often treated with antibiotics like penicillin, ampicillin, tetracycline, and gentamycin, which can be given directly into the udder or through injections. An effective antibiotic treatment strategy to control mastitis is Dry Cow Therapy (DCT). During the dry period when cows are not producing milk, infections need to be addressed promptly to ensure they do not affect the next lactation period. After the last milking, they are checked for any signs of mastitis and administered antibiotics if necessary, eliminating existing infections and preventing new ones during the dry period. Since the cow's milk may contain antibiotic residues after treatment, the dry period is the best time to treat mastitis to reduce the risk of incorporating antibiotics into the food chain [5].
Antibiotic residues in milk can cause allergies and drug resistance in consumers. Therefore, milk with antibiotic residues must be discarded, leading to financial loss for dairy farms. Furthermore, antibiotics do not prevent long-term damage to the udder, which can reduce the cow's milk production over its lifetime and cause further economic losses [5].
Prevention of Mastitis
Preventing mastitis involves implementing good management practices, maintaining hygiene, and ensuring optimal cow health. Key prevention strategies include:
Proper milking hygiene: Clean and sanitize udders before and after milking, use well-maintained milking equipment, and employ proper milking techniques.
Environmental management: Keep barns clean and dry, provide comfortable bedding, and ensure good ventilation to reduce bacterial load.
Regular health checks: Monitor udder health regularly, conduct SCC testing, and promptly address any signs of infection.
Vaccination: Vaccinating cows against common mastitis bacteria such as Staph. aureus, Strep. agalactiae, and E. coli can prevent infections. However, vaccination alone is not effective in preventing mastitis due to the wide diversity in pathogens and strains causing mastitis.
Nutrition and stress management: Provide a balanced diet and minimize stress to support the immune system [5].
About Kraken Sense
Kraken Sense develops all-in-one pathogen detection solutions to accelerate time to results by replacing lab testing with a single field-deployable device. Our proprietary device, the KRAKEN, has the ability to detect bacteria and viruses down to 1 copy. It has already been applied for epidemiology detection in wastewater and microbial contamination testing in food processing, among many other applications. Our team of highly-skilled Microbiologists and Engineers tailor the system to fit individual project needs. To stay updated with our latest articles and product launches, follow us on LinkedIn, Twitter, and Instagram, or sign up for our email newsletter. Discover the potential of continuous, autonomous pathogen testing by speaking to our team.