Mastitis is an inflammation of the mammary gland in dairy cows, representing the most prevalent and financially burdensome disease in the dairy industry globally. The condition is primarily triggered by bacterial pathogens that invade the udder through the teat canal, initiating a localized immune response. This inflammatory reaction damages the milk-producing tissue, resulting in decreased milk yield and compromised milk quality. The economic impact is substantial, with global losses estimated in the billions of dollars annually, driven by veterinary costs, discarded milk, and premature culling.
Recognizing the Infection: Types and Symptoms
Mastitis is generally categorized into two distinct forms based on the visibility of symptoms: clinical and subclinical mastitis. Clinical mastitis presents with easily observable abnormalities in the cow’s udder or the milk itself. The udder may show signs of inflammation, such as swelling, heat, redness, or hardness.
The milk from an infected quarter often appears visibly altered, exhibiting a watery consistency, flakes, clots, or pus. In severe cases, the cow may also display systemic signs of illness, including a fever, loss of appetite, dehydration, and reduced mobility. Immediate attention is necessary for these clinical cases to prevent the infection from becoming life-threatening.
In contrast, subclinical mastitis is far more common, yet it remains hidden because it shows no visible changes in the milk or the udder. This form is identified through diagnostic testing that measures the cow’s immune response to the infection. The primary method involves detecting an elevated Somatic Cell Count (SCC) in the milk.
Somatic cells are predominantly white blood cells that rush into the mammary gland to fight invading bacteria, and their concentration increases significantly during infection. Farmers can screen for subclinical cases on-farm using the California Mastitis Test (CMT), which causes the milk sample to gel based on the SCC level. This form causes the majority of economic losses due to its chronic effect on milk production, with affected cows potentially losing over 1,500 pounds of milk per lactation.
Sources of Infection and Key Risk Factors
Mastitis pathogens are broadly divided into two groups based on their origin and spread, which dictates the control strategy. Contagious pathogens primarily reside in the infected mammary gland and are transmitted from cow to cow, often during milking. Classic examples include Staphylococcus aureus and Streptococcus agalactiae, which colonize the teat skin and teat canal.
The transfer of these bacteria occurs via contaminated milking clusters, milkers’ hands, or shared udder cloths. Infections caused by these bacteria tend to be chronic and subclinical, persisting within the herd unless targeted interventions are implemented. Managing these pathogens requires strict hygiene protocols during milking to prevent transmission.
Environmental pathogens, conversely, originate from the cow’s surroundings, such as bedding, soil, water, and manure. Common examples are Escherichia coli (E. coli) and Streptococcus uberis. Infection typically happens between milkings when the cow lies down, exposing the teat end to a high concentration of organisms.
Non-pathogen risk factors also increase a cow’s susceptibility to infection. Poor housing hygiene resulting in wet or dirty conditions is a major contributor to environmental mastitis. Faulty milking equipment, such as an improperly functioning vacuum or worn-out liners, can cause teat-end damage, making it easier for bacteria to penetrate the teat canal. Inadequate nutrition, which compromises the cow’s immune status, and stress also increase the risk of developing a new intramammary infection.
Proactive Management: Comprehensive Prevention Strategies
The most effective approach to managing mastitis involves a comprehensive, multi-faceted prevention program that targets both pathogen types and minimizes cow susceptibility. Milking time hygiene is a cornerstone of this strategy, beginning with the use of a pre-milking teat dip. This germicidal solution is applied to the teats, allowed a contact time of at least 30 seconds, and then thoroughly dried with a single-use towel before the milking unit is attached. This process significantly reduces environmental bacteria on the teat surface, preventing them from being forced into the udder during milking.
Post-milking teat dipping is equally important, as it immediately kills any mastitis-causing organisms that may have contaminated the teat end during milking. The application of an approved post-dip solution, often containing iodine or chlorhexidine, forms a protective barrier over the teat canal orifice, which remains slightly open after milking. This practice is recognized as the single most effective measure for reducing new infections, particularly those caused by contagious bacteria.
Environmental control focuses on keeping the cow’s living spaces clean and dry, reducing the reservoir of environmental pathogens. Bedding materials must be managed meticulously, as organic bedding like straw or wood shavings can harbor high bacterial counts, especially when wet. Regular cleaning and replacement of bedding, along with ensuring dry lanes and resting areas, minimize the exposure of the teat end to manure and soil.
Proper dry cow management is a distinct preventive phase that occurs when lactation ceases, as this period carries a high risk for new infections. Dry cow therapy involves infusing an intramammary antibiotic into each quarter after the final milking, aiming to cure any existing subclinical infections. This step is often paired with an internal teat sealant, a non-antibiotic product that physically blocks the teat canal for the entire dry period, preventing new bacterial invasions.
Equipment maintenance completes the prevention loop, ensuring the milking machine operates correctly and does not compromise the teat’s natural defenses. Regular inspection and servicing of components, such as liners and vacuum regulators, prevent damage to the teat end that could facilitate bacterial entry. A well-maintained machine prevents issues like liner slippage, which can cause an infectious milk aerosol to be thrust against the teat end.
Intervention and Recovery: Treatment Options
Once a cow is diagnosed with mastitis, intervention protocols depend on the severity of the clinical signs. For mild to moderate cases, the mainstay of treatment involves intramammary antibiotic infusions, delivered directly into the infected quarter via the teat canal. This localized application allows high concentrations of the medication to reach the site of infection.
For severe cases where the cow is systemically ill with a high fever, systemic antibiotics administered via injection are necessary to combat the infection throughout the body. Supportive care is also a component of therapy, frequently including non-steroidal anti-inflammatory drugs (NSAIDs) to reduce pain, swelling, and fever. Frequent stripping of the affected quarter, manually removing the infected milk, helps to flush out the bacteria and inflammatory products.
Not all cases require antibiotics, especially mild cases caused by certain environmental pathogens like E. coli, which often resolve naturally. Treatment decisions should be guided by a veterinarian and based on milk culture results to ensure the correct antibiotic is chosen for the specific pathogen. Adherence to milk and meat withdrawal periods is necessary after any antibiotic treatment to prevent drug residues from entering the human food supply.