Background

Subclinical bovine mastitis is a condition in dairy cows where there is an inflammation of the udder without noticeable clinical signs. Unlike clinical mastitis, which presents with visible changes in the milk, udder, or the cow’s general health, subclinical mastitis is often asymptomatic and can go unnoticed for an extended period. 

The primary cause of subclinical mastitis is bacterial infections. Many times, bacteria, including Escherichia coli, Streptococcus agalactiae, and Staphylococcus aureus, are responsible. These pathogens can enter the udder through the teat canal, causing inflammation and affecting milk quality. Subclinical mastitis is characterized by its asymptomatic nature. Cows with subclinical mastitis do not show obvious signs of illness, and the udder may appear normal. However, the milk from affected quarters may contain elevated somatic cell counts (SCC), indicating an immune response to infection. 

Although subclinical mastitis may not cause overt clinical signs, it has a significant economic impact on the dairy industry. The presence of subclinical mastitis can lead to decreased milk production, lower milk quality, increased somatic cell counts, and higher rates of culling due to reduced reproductive performance. 

Epidemiology

Prevalence: 

• Subclinical mastitis is widespread in dairy herds worldwide. The prevalence can vary among regions, herds, and individual cows. 
• It is estimated that a significant percentage of dairy cows may be affected by subclinical mastitis at any given time. 

Pathogens: 

• Different bacterial pathogens contribute to subclinical mastitis. Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, and coagulase-negative staphylococci are commonly associated with subclinical mastitis cases. 
• Understanding the prevalence of specific pathogens can help tailor control and treatment strategies. 

Transmission: 

• Bacterial pathogens causing mastitis can be transmitted from cow to cow during milking, through contaminated milking equipment, and via environmental sources. 
• The teat canal provides a route for bacteria to enter the udder, leading to infection. 

Somatic Cell Counts (SCC): 

• Elevated somatic cell counts in milk are used as an indicator of mastitis. Monitoring SCC is a common method for assessing the prevalence of subclinical mastitis within a herd. 
• Bulk tank milk SCC is often measured to provide an overall indication of udder health in a herd. 

Herd Health Management: 

• Controlling subclinical mastitis requires effective management strategies. This includes proper milking hygiene, regular monitoring, and culling of chronically infected cows. 
• Vaccination strategies and genetic selection for mastitis resistance are also considered in herd health management. 

Geographical Variation: 

• The prevalence and epidemiology of subclinical mastitis can vary geographically due to differences in farming practices, climate, and management strategies. 

Economic Impact: 

• The economic consequences of subclinical mastitis, including reduced milk production and quality, contribute to its significance in the dairy industry. 

Anatomy

Pathophysiology

Bacterial Entry and Invasion: 

• Bacterial pathogens enter the udder through the teat canal, which serves as the primary route of infection. Common mastitis-causing bacteria include Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, and others. 
• Contamination can occur during the milking process, through contact with contaminated bedding or the environment, or via ascending infections from the teat end. 

Host Defense Mechanisms: 

• The cow’s immune system plays a crucial role in responding to invading pathogens. Neutrophils, a type of white blood cell, are the primary cells involved in the immune response against bacterial infections. 
• In subclinical mastitis, the immune response may not be strong enough to cause visible clinical signs, but it can lead to an increase in somatic cell counts (SCC) in milk. SCC is a marker of inflammation and immune cell activity. 

Inflammation and Immune Response: 

• The presence of bacteria in the udder triggers an inflammatory response. Immune cells, particularly neutrophils, migrate to the site of infection to combat the invading pathogens. 
• Immune cells are attracted to and activated by mediators of inflammation, such as cytokines and chemokines. These mediators can also contribute to the clinical and subclinical manifestations of mastitis. 

Mammary Gland Tissue Damage: 

• Prolonged or recurrent subclinical mastitis episodes can lead to damage to the mammary gland tissue. Chronic inflammation may result in fibrosis and changes in the structure of the udder. 
• Tissue damage can impact milk production and quality, contributing to economic losses in dairy farming. 

Elevated Somatic Cell Counts (SCC): 

• One of the key indicators of subclinical mastitis is an increase in somatic cell counts in milk. These cells, primarily composed of neutrophils, are shed into the milk as a response to inflammation. 
• High SCC can negatively affect milk quality and may be used as a diagnostic marker for subclinical mastitis. 

Etiology

Bacterial Pathogens: Bacterial infections are the leading cause of subclinical mastitis in dairy cows. Various bacteria can be responsible for the condition, and their prevalence may vary. Common mastitis-causing bacteria include: 

• Staphylococcus aureus 
• Streptococcus agalactiae 
• Escherichia coli 
• Coagulase-negative staphylococci 
• Streptococcus uberis 
• Mycoplasma spp. 

Environmental Contamination: The environment in which dairy cows are housed and milked can contribute to the introduction and spread of mastitis-causing bacteria. The danger of bacterial infiltration into the udder might be increased by moist environment, contaminated bedding, and filthy milking equipment. 

Milking Procedures: Inadequate milking procedures or improper milking machine function can contribute to the development of subclinical mastitis. Poor milking hygiene, incomplete milking, and improper teat preparation may create conditions conducive to bacterial entry and infection. 

Teat Health: The condition of the teats and teat canal is crucial in preventing bacterial invasion. Injuries, chapping, or other damage to the teat end can provide entry points for bacteria. Maintaining good teat health is essential in preventing mastitis. 

Host Factors: Individual cow factors, including the cow’s immune status and genetic predisposition, can influence susceptibility to mastitis. Cows with weaker immune responses may be more prone to subclinical mastitis. 

Stress and Nutrition: It can weaken the immune system, making cows more susceptible to infections. Management practices that address stress reduction and provide proper nutrition contribute to overall udder health. 

Seasonal Variation: Seasonal factors, such as temperature and humidity, can influence the prevalence of mastitis. Warm and humid conditions may create an environment conducive to bacterial growth, increasing the risk of infection. 

Mammary Gland Structure: The anatomy and structure of the mammary gland can impact susceptibility to mastitis. Structural abnormalities or variations in udder conformation may create conditions that facilitate bacterial entry and colonization. 

Herd Health Management: The overall management practices within a dairy herd, including biosecurity measures, vaccination programs, and culling strategies, play a role in preventing and managing subclinical mastitis. 

Genetics

Prognostic Factors

• Somatic Cell Counts (SCC): Elevated SCC in milk is a common indicator of subclinical mastitis. Prognostically, the level of SCC can provide information about the severity of the infection and the response to treatment. Persistent high SCC may suggest chronicity. 

• Pathogen Type: The specific bacterial pathogen causing subclinical mastitis can influence the prognosis. Some bacteria may respond better to treatment, while others may lead to chronic infections. Identification of the pathogen through microbiological analysis helps in tailoring treatment plans. 
• Duration of Infection: The length of time that subclinical mastitis has been present can impact the prognosis. Chronic infections are often more challenging to treat and may result in long-term damage to the mammary gland. 
• Treatment Response: The response of the cow to treatment, especially antibiotic therapy, is a crucial prognostic factor. Cows that respond well to treatment and show a reduction in SCC are more likely to recover fully. 
• Udder Health History: The past udder health history of the cow, including previous cases of mastitis, can influence the prognosis. Cows with a history of recurrent mastitis may be more prone to chronic infections. 
• Immune Status: The immune status of the cow plays a role in the prognosis. Cows with a robust immune response may have a better prognosis for recovery. On the other hand, immunocompromised cows may struggle to clear infections.

Clinical History

Clinical Presentation: 

• Visual Changes in the Udder: Swelling, redness, and heat may be noticeable in the udder affected by mastitis. The udder may appear asymmetrical. 
• Pain and Tenderness: Affected quarters may be painful and sensitive to touch. Cows may exhibit signs of discomfort during milking. 
• Changes in Milk: The milk from the affected quarter may show visible changes such as clots, discoloration, or an increase in somatic cell counts (SCC). It may also have an abnormal odor. 
• Systemic Signs: In severe cases, cows may exhibit systemic signs such as fever, lethargy, and a decrease in appetite. 

Age Group: 

• Clinical mastitis can affect cows of all age groups, but it is more commonly observed in older cows, especially those in mid-lactation or late lactation stages. 
• Heifers and first-calf heifers may also be susceptible, particularly if they experience stress or have compromised immune systems. 

Associated Comorbidity or Activity: 

• Stress Factors: Stressors such as transportation, changes in diet, or adverse environmental conditions can contribute to the development of clinical mastitis. 
• High Milk Production: Cows in peak lactation, producing high volumes of milk, may be more prone to mastitis. 
• Teat Injury: Injuries to the teats, caused by improper milking procedures or trauma, can increase the risk of bacterial entry and mastitis. 

Acuity of Presentation: 

• Acute Onset: Clinical mastitis often has an acute onset, with a sudden appearance of symptoms. The udder may become visibly affected over a short period. 
• Rapid Progression: The severity of clinical mastitis can progress rapidly, leading to systemic signs and a decline in the overall health of the cow. 
• Chronic Cases: In some instances, clinical mastitis can become chronic, with persistent symptoms and a prolonged recovery period. 

Physical Examination

• Udder Inspection: Although subclinical mastitis may not cause visible changes in the udder, a thorough inspection is still essential. Look for subtle signs such as asymmetry between quarters, changes in udder texture, or mild swelling that may not be immediately apparent. 
• Palpation of the Udder: Gently palpate the udder to detect any areas of heat, tenderness, or firmness. In subclinical cases, these signs may be mild or absent, but palpation can provide valuable information. 
• Teat Inspection: Examine each teat individually for signs of abnormalities, such as swelling, redness, or heat. Inspect the teat ends for any lesions, cracks, or injuries that may serve as entry points for bacteria. 
• Milk Color and Consistency: While not a direct physical examination, observing the color and consistency of milk can provide insights into subclinical mastitis. Subclinical cases may not present obvious changes, but alterations in milk appearance (e.g., increased somatic cell counts) could be indicative. 
• Milk Yield: A decrease in milk yield from one or more quarters, even if subtle, might be a sign of subclinical mastitis. Regular monitoring of milk production can help identify changes that warrant further investigation. 
• Behavioral Changes: Subtle changes in a cow’s behavior, such as increased restlessness or discomfort during milking, may be indicative of subclinical mastitis. Observing the cow’s response to milking can provide additional clues. 

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

• Normal Physiological Variations: Fluctuations in somatic cell counts (SCC) can occur even in healthy cows. It’s essential to establish baseline SCC values for individual cows and monitor for significant deviations. 
• Seasonal Variation: Environmental factors, such as changes in weather or management practices, can influence SCC. Seasonal variations may affect milk quality and should be considered in the differential diagnosis. 
• Transient Infections: Cows may experience transient infections that result in temporary increases in SCC. These infections may resolve on their own without progressing to clinical mastitis. 
• Teat Injuries: Injuries to the teats, caused by trauma or improper milking procedures, can lead to changes in milk quality. Differentiating between injury-related changes and subclinical mastitis is important. 
• Bacterial Contamination during Milking: External contamination of milk during milking, possibly due to poor milking hygiene or contaminated equipment, can lead to temporary changes in milk quality. Adequate hygiene practices can help prevent this. 
• Environmental Factors: Changes in the cow’s environment, such as exposure to wet or dirty conditions, may influence milk quality. Proper management practices can mitigate environmental factors. 
• Mycotic Infections: Fungal or yeast infections of the udder may affect milk quality. These infections can sometimes be mistaken for subclinical mastitis, and laboratory tests may be necessary for accurate diagnosis. 
• Inflammation due to Other Causes: Inflammation in the udder can occur due to reasons other than bacterial infections, such as injury or irritation.  

• Stress-Related Changes: Stressors such as transportation, changes in diet, or disturbances in the cow’s routine can result in temporary changes in milk quality. Minimizing stress and providing consistent management practices can help. 

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

Diagnosis and Identification: 

• Regular monitoring of somatic cell counts (SCC) in milk is crucial for early detection. An increase in SCC serves as an indicator of subclinical mastitis. 
• Individual cow records should be maintained to track changes in SCC over time, facilitating the identification of cows requiring intervention. 

Bacterial Culture and Sensitivity Testing: 

• To determine the precise culprit causing the infection, sensitivity testing and bacterial culture might be performed if clinical symptoms or a persistently high SCC are noted. This information influences the choice of appropriate antimicrobial medication. 

Management Practices: 

• Implementing good management practices is essential for the successful treatment of subclinical mastitis. This includes maintaining proper milking hygiene, ensuring clean and dry bedding, and providing a comfortable environment for the cows. 

Selective Dry Cow Therapy: 

• Using intramammary antibiotics to treat current infections and prevent new ones during the dry phase is known as selected dry cow therapy, and it is used for cows diagnosed with subclinical mastitis that occurs at the end of lactation. 

Antimicrobial Therapy: 

• In cases where bacterial culture indicates the presence of specific pathogens, targeted antimicrobial therapy may be initiated. It’s important to use antibiotics that are effective against the identified bacteria. 
• Veterinarians may recommend systemic or intramammary antibiotic treatments depending on the severity of the infection. 

Extended Therapy or Re-Treatment: 

• In some cases, extended antibiotic therapy or re-treatment may be necessary to ensure complete eradication of the infection. This decision is often based on follow-up SCC measurements and veterinary assessment. 

Monitoring and Follow-Up: 

• Regular monitoring of SCC and milk quality is essential to assess the response to treatment. Follow-up tests help determine the success of interventions and identify any cows that may need additional attention. 

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

use-of-a-non-pharmacological-approach-for-treating-subclinical-bovine-mastitis

Hygiene Management: 

• Proper Milking Techniques: Ensure a clean and sanitized milking environment, including the udder and teats, to prevent the introduction of bacteria. 
• Regular Udder Cleaning: Regularly clean and dry the udder to reduce the risk of bacterial contamination. 

Nutritional Management: 

• Balanced Diet: Provide a well-balanced and nutritionally adequate diet to support the cow’s immune system and overall health. 
• Supplemental Nutrients: Supplement the diet with essential nutrients like vitamins and minerals to boost the cow’s immune response. 

Environmental Control: 

• Stress Reduction: Minimize stress factors in the environment, as stress can weaken the cow’s immune system. 
• Comfortable Housing: Provide comfortable and clean housing conditions to reduce the risk of infections. 

Teat Health: 

• Regular Checking: Monitor the condition of teats and udder regularly for any signs of abnormalities. 
• Proper Teat Dipping: Use appropriate teat dips after milking to prevent bacterial contamination. 

Management Practices: 

• Culling Infected Cows: Consider culling persistently infected cows to prevent the spread of subclinical mastitis within the herd. 
• Proper Record Keeping: Maintain detailed records of each cow’s health, milk production, and any signs of mastitis for early detection and intervention. 

Use of Natural Products: 

• Herbal Remedies: Some herbal extracts, like aloe vera or calendula, may have anti-inflammatory and antibacterial properties.  
• Essential Oils: Essential oils such as tea tree oil or lavender oil, may have antimicrobial properties. However, their use should be approached cautiously and under veterinary guidance. 

Regular Monitoring and Testing: 

• Milk Quality Testing: Regularly test milk quality to detect changes indicative of subclinical mastitis. 
• Somatic Cell Count (SCC) Monitoring: Keep track of SCC levels, as an elevated count can indicate mastitis. 

Use of Intramammary Antibiotics in the treatment of subclinical bovine mastitis

The use of intramammary antibiotics is a common and effective approach in the treatment of subclinical mastitis in dairy cows. Intramammary antibiotics are directly applied to the affected udder quarter, providing a targeted treatment for the localized infection. Commonly used intramammary antibiotics for the treatment of subclinical mastitis include penicillin, ampicillin, cloxacillin, and cephalosporins. The choice depends on the causative bacteria and their susceptibility to specific antibiotics. 

Intramammary antibiotics are typically administered by infusing a specially formulated antibiotic-containing product directly into the teat canal. This can be done using a sterile applicator or a syringe. 

Use of Anti-inflammatory drugs in the treatment of subclinical bovine mastitis

Anti-inflammatory drugs, particularly non-steroidal anti-inflammatory drugs (NSAIDs), may be used in the treatment of subclinical bovine mastitis to reduce inflammation and alleviate pain associated with the condition. Inflammation is a common response to infection, and it can contribute to pain and swelling in the udder. NSAIDs work by inhibiting certain enzymes involved in the inflammatory process, thus reducing inflammation. Mastitis can be painful for the cow, and NSAIDs can help provide relief by reducing pain and discomfort. 

• Flunixin Meglumine: This NSAID is commonly used in veterinary medicine to control inflammation and provide analgesia. 
• Meloxicam: Another NSAID that may be used for its anti-inflammatory and analgesic properties. 

use-of-intervention-with-a-procedure-in-treating-subclinical-bovine-mastitis

Udder Infusion or Intramammary Therapy: 

• Purpose: Like antibiotic infusion, this involves introducing therapeutic substances directly into the udder to target the infection. 
• Procedure: A sterile solution containing therapeutic agents (antibiotics, anti-inflammatories, or other substances) is infused into the affected teat through the teat canal. 

Udder Massage and Milking: 

• Purpose: Massage and milking can help stimulate milk flow and promote drainage of the udder, reducing the accumulation of infected milk. 
• Procedure: Gentle udder massage and milking can be performed by hand or using mechanical milking equipment. 

Teat Sealing: 

• Purpose: Used as part of dry cow therapy, teat sealing involves sealing the teat canal to prevent new infections during the dry period. 
• Procedure: A sterile substance, often an antibiotic-containing infusion or teat sealant, is introduced into the teat canal to create a barrier. 

Debridement or Teat Canal Cleaning: 

• Purpose: Cleaning the teat canal can help remove debris and bacteria, promoting healing and reducing the risk of reinfection. 
• Procedure: This may involve gentle cleaning of the teat canal using sterile solutions and appropriate tools. 

Teat Surgery: 

• Purpose: In certain severe cases or cases with structural issues, surgical interventions may be considered. 
• Procedure: Surgical procedures could include the correction of teat abnormalities or addressing conditions that contribute to chronic subclinical mastitis. 

Diagnostic Procedures: 

• Purpose: In some cases, diagnostic procedures such as milk culture or somatic cell count testing may be performed to identify the specific causative agent. 
• Procedure: Diagnostic procedures involve collecting samples of milk or udder tissue for laboratory analysis to determine the type of infection and guide treatment decisions. 

Thermotherapy: 

• Purpose: Applying heat to the udder can promote blood circulation and may have a therapeutic effect. 
• Procedure: This may involve using warm compresses or specialized heat therapy devices on the udder. 

Lactation Management: 

• Purpose: Adjusting the lactation cycle and milking frequency can be part of a comprehensive approach to managing subclinical mastitis. 
• Procedure: Lactation management may involve modifications to the milking routine, including adjusting milking machine settings and practices. 

use-of-phases-in-managing-subclinical-bovine-mastitis

Prevention Phase: 

• Udder Hygiene: Implementing good udder hygiene practices, such as regular cleaning and sanitization, to prevent the introduction of bacteria during milking. 
• Dry Cow Management: Employing dry cow therapy, which involves administering intramammary antibiotics at the end of lactation to treat existing infections and prevent new infections during the dry period. 
• Nutritional Management: Providing a well-balanced diet with proper nutrition to support the cow’s immune system and overall health. 
• Environmental Management: Reducing stress, offering cozy housing, and keeping the surroundings dry and clean will all help lower the chance of infection. 

Monitoring Phase: 

• Regular Milk Quality Testing: Conducting routine milk quality testing, including somatic cell count (SCC) monitoring, to detect changes indicative of subclinical mastitis. 
• Individual Cow Monitoring: Regularly checking individual cows for signs of mastitis, such as changes in udder appearance or milk quality, and maintaining detailed health records. 
• Periodic Udder Health Checks: Engaging in periodic udder health checks, including physical examinations and diagnostic procedures, to identify subclinical mastitis early. 

Treatment Phase: 

• Pharmaceutical Intervention: Administering appropriate intramammary antibiotics for treating bacterial infections associated with subclinical mastitis. This may be done during lactation or as part of dry cow therapy. 
• Anti-inflammatory Drugs: Using non-steroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation and alleviate pain associated with mastitis. 
• Supportive Therapies: Implementing supportive therapies, such as immune system boosters, to aid the cow’s natural defenses. 

Post-Treatment Monitoring Phase: 

• Follow-Up Testing: Conducting follow-up milk quality testing to assess the effectiveness of the treatment and ensure the resolution of the infection. 
• Observational Monitoring: Continuously monitoring individual cows for any signs of recurrence or persistence of mastitis, adjusting the treatment plan as needed. 

Herd Health Management: 

• Culling Decisions: Considering culling for persistently infected cows that do not respond to treatment, to prevent the spread of subclinical mastitis within the herd. 
• Herd Vaccination Programs: Exploring the use of herd vaccination programs to prevent specific mastitis-causing pathogens. 

Record Keeping and Analysis: 

• Detailed Records: Maintaining detailed records of each cow’s health, milk production, and any signs of mastitis for analysis and decision-making. 
• Data Analysis: Regularly analyzing data on milk quality, SCC levels, and treatment outcomes to identify trends and areas for improvement in mastitis management practices. 

Medication

Future Trends

Media Gallary

References

Bovine Mastitis:ncbi.nlm.nih 

Udder Health Monitoring:ncbi.nlm.nih 

Prevalence of subclinical mastitis:ncbi.nlm.nih 

Efficacy of intramammary:ncbi.nlm.nih