Mastitis is the most common disease affecting dairy cattle and a persistent issue for farms globally. The condition is an inflammation of the mammary gland (udder), usually caused by a bacterial infection. This disease compromises animal well-being and has a significant economic impact due to its effect on milk production and quality.
What is Mastitis in Dairy Cows?
Mastitis is an inflammatory response in the mammary gland tissue, caused by microorganisms that enter through the teat canal. These pathogens, primarily bacteria, multiply and release toxins that damage the udder’s milk-producing tissues. The resulting inflammation disrupts normal milk synthesis and alters the milk’s composition and appearance.
The disease has two forms: clinical and subclinical. Clinical mastitis presents with visible abnormalities, including a swollen, red, or hot udder that may be painful to the touch. The milk from an infected quarter can appear watery, discolored, or contain flakes, clots, or blood. In severe cases, the cow may exhibit systemic illness, such as fever, loss of appetite, and dehydration.
Subclinical mastitis is a hidden form of the disease, showing no obvious signs of inflammation or changes in the milk. Despite the lack of visible symptoms, the infection is actively harming udder tissue and reducing milk output. This form is identified through tests that measure the somatic cell count (SCC) in milk, which are white blood cells that increase to fight the infection. A high SCC is a reliable indicator of subclinical mastitis.
Sources of Infection and Risk Factors
The cause of mastitis is a bacterial infection that breaches the teat canal. These bacteria are categorized into two groups: contagious and environmental. Contagious pathogens spread from an infected cow to a healthy one during the milking process. These organisms live on the skin of the udder or within infected glands and are transferred via milking equipment, towels, or the hands of milkers.
Environmental pathogens are widespread in the cow’s living area, thriving in bedding, soil, manure, and contaminated water. Cows are exposed to these bacteria between milkings when their teat ends come into contact with soiled surfaces. The risk of infection from environmental sources is high when housing conditions are wet and dirty.
Several risk factors increase a cow’s susceptibility to mastitis. Poor hygiene in the milking parlor or housing areas fosters a high pathogen load. Malfunctioning or improperly maintained milking equipment can damage teat ends, creating an entry point for bacteria. Cow-specific factors also play a role, as animals in early or late lactation, older cows, and those with compromised immune systems are more vulnerable. Teat shape and existing lesions can also make it easier for bacteria to invade.
Detecting and Managing Mastitis Cases
Early and accurate detection is necessary for managing mastitis effectively. For clinical cases, daily observation is key. Farmers visually inspect the udder for signs of swelling or redness and examine the first few streams of milk for any abnormalities like clots or discoloration before every milking. This practice, known as forestripping, allows for prompt identification.
To detect the subclinical form, farmers rely on indirect measures. The California Mastitis Test (CMT) is a cow-side test that involves mixing a reagent with milk from each quarter. The reagent reacts with somatic cells, causing the mixture to thicken in proportion to the SCC and providing a rough estimate of inflammation. More precise individual cow SCC data is often provided by routine milk recording services. For a definitive diagnosis, milk samples can be sent to a laboratory for bacterial culture.
Once mastitis is detected, a management plan is created with a veterinarian. Clinical mastitis treatment commonly involves intramammary antibiotics infused directly into the infected quarter. Farmers must adhere to prescribed withdrawal times for both milk and meat to ensure no antibiotic residues enter the food supply. Supportive care, such as anti-inflammatory drugs and more frequent milking of the affected quarter, may also be administered.
Management of subclinical cases focuses on long-term strategies. This can include specific antibiotic treatments during the cow’s dry (non-milking) period. In persistent cases, culling chronically infected animals from the herd may be necessary.
Farm Strategies for Mastitis Prevention
Preventing new infections is the most effective approach to controlling mastitis. A prevention program revolves around strict hygiene protocols during the milking routine. This includes cleaning and disinfecting teats with a pre-dip solution and then thoroughly drying them before the milking unit is attached. After milking, a post-milking teat dip is applied as a germicidal barrier to protect the open teat canal.
Proper function and maintenance of the milking equipment are also important. Regular servicing ensures that vacuum levels are correct and that liners are replaced on schedule to avoid causing damage to the teats. Ensuring milking units are attached and removed gently prevents unnecessary stress on the udder.
The cow’s environment plays a large role in exposure to environmental pathogens. Keeping housing areas, especially bedding, clean and dry reduces the population of bacteria the cow’s udder is exposed to between milkings. Well-designed barns with adequate ventilation also contribute to a healthier environment.
Herd health management strategies are another layer of defense. Many farms utilize dry cow therapy, where quarters are treated with a long-acting antibiotic at the end of lactation to clear up existing infections and prevent new ones. Teat sealants may also be used to provide a physical barrier. To manage contagious mastitis, infected cows are segregated and milked last, and chronically infected animals may be culled.
The Wider Consequences of Mastitis
The impact of mastitis extends beyond an individual cow, creating significant economic, quality, and welfare challenges. For dairy farmers, the economic losses are substantial and come from several sources:
- Reduced milk production, as an inflamed udder produces less milk.
- Discarded milk from treated cows.
- Expenses for antibiotics and veterinary services.
- Increased labor for managing sick animals.
- Premature culling of cows that can no longer produce high-quality milk.
Mastitis also affects the quality of milk. The inflammation process alters its composition, leading to changes in protein and fat content and a shorter shelf life. The presence of high somatic cell counts is a key indicator of poor quality. Consumers can be assured of safety, as all commercially sold milk is pasteurized, a process that kills harmful bacteria.
From an animal welfare perspective, mastitis is a serious concern. The inflammation of the udder is painful and distressing for the cow, causing discomfort and affecting her mobility and behavior. Severe, acute cases can lead to systemic illness and, in some instances, can be fatal. The pain and stress associated with the disease underscore the importance of prevention and control programs.