Coagulase-negative staphylococci (CNS) have become increasingly recognised as significant contributors to mastitis in dairy cows. While often overshadowed by more notorious pathogens like Staphylococcus aureus and Streptococcus, CNS species represent a large group of bacteria that can cause subclinical and clinical mastitis. This type of infection can have a notable impact on milk production and quality, particularly in herds where control measures are not stringent.
In this guide, we’ll delve into how CNS bacteria affect dairy cows, the challenges of detection, and the management strategies necessary to limit their influence on milk yield and cow health.
Understanding Coagulase-Negative Staphylococci (CNS)
CNS refers to a diverse group of staphylococcal species that lack the enzyme coagulase, distinguishing them from their coagulase-positive counterparts like Staphylococcus aureus. Species within this group, such as Staphylococcus chromogenes, Staphylococcus epidermidis, and Staphylococcus simulans, are commonly found on the skin of dairy cows and within their environment.
For years, CNS bacteria were considered relatively benign, often dismissed as contaminants in milk cultures. However, recent studies have shown that these bacteria can contribute to mastitis, particularly in dairy cows with weakened immunity or compromised udder defences.
How CNS Bacteria Cause Mastitis
CNS species generally enter the udder through the teat canal, similarly to other mastitis-causing bacteria. They typically infect cows with damaged or weakened teats, often during or after the milking process. While CNS infections are often less aggressive than those caused by S. aureus or Streptococcus, they can still result in significant disruptions to milk production and cow health, especially if they go undetected.
- Subclinical Mastitis: CNS is most commonly associated with subclinical mastitis. This form of mastitis does not produce noticeable symptoms, making it challenging for farmers to detect without regular milk testing. However, subclinical mastitis can lead to elevated somatic cell counts (SCC), an important marker of udder health and milk quality.
Cows infected with CNS may appear healthy and continue to produce milk, but the milk can be of lower quality due to increased SCC levels. High SCC indicates an ongoing immune response within the udder, which can affect milk’s shelf life and reduce its value. - Mild Clinical Mastitis: In some cases, CNS infections can progress to mild clinical mastitis. Signs may include:
- Slight swelling or redness in the udder.
- Changes in milk appearance, such as watery milk or small clots.
- Slight drops in milk yield, particularly in individual quarters.
- Unlike severe mastitis caused by more aggressive pathogens, CNS-induced clinical mastitis tends to resolve more quickly, either spontaneously or with minimal treatment. However, chronic or recurrent infections may occur, leading to persistent production losses.
The Challenges of Detecting CNS Mastitis
One of the primary challenges in managing CNS mastitis is that infections often remain undetected until they have already impacted milk quality. Since CNS infections tend to present subclinically, they may not cause obvious symptoms, such as swelling or changes in milk consistency. Therefore, routine milk testing is crucial for identifying these infections before they affect overall herd performance.
- Somatic Cell Count (SCC) Monitoring: The first sign of CNS mastitis is usually an elevated SCC. Regular monitoring of individual cow SCC levels is critical for early detection of subclinical mastitis. Bulk tank SCC can also provide insight into overall herd udder health, but individual testing is necessary to pinpoint affected cows.
- Milk Culturing: Milk cultures are the gold standard for diagnosing CNS infections. By culturing milk samples, farmers and veterinarians can identify the bacterial species causing mastitis and tailor their treatment and management strategies accordingly. Due to the prevalence of CNS in subclinical cases, routine culturing is advised even without clinical signs.
The Impact of CNS on Milk Production and Herd Health
While CNS mastitis is often considered less severe than infections caused by other pathogens, its impact on milk production can be significant, especially in large herds. Even though CNS infections tend to be mild or subclinical, their effects accumulate over time. Elevated SCC leads to:
- Reduced milk yield, as the cow’s immune system diverts energy towards fighting the infection rather than producing milk.
- Lower milk quality, as increased SCC affects the composition of milk, reducing its market value.
- Economic losses, not only from decreased milk production but also from milk that must be discarded due to poor quality or antibiotic residues after treatment.
Cows with chronic or recurrent CNS infections may experience a gradual decline in productivity, and the overall SCC of the herd may rise, leading to penalties or milk rejection by processors.
Best Practices for Preventing CNS Mastitis
Given the subclinical nature of CNS infections, prevention is key to maintaining a healthy, productive dairy herd. Implementing the following management practices can help reduce the risk of CNS mastitis and improve udder health:
- Good Milking Hygiene: Proper milking procedures are essential for preventing the spread of CNS bacteria. This includes:
- Pre- and post-milking teat disinfection to remove bacteria from the teat surface before milking and prevent reinfection after milking.
- Clean and well-maintained milking equipment to avoid contamination of teats with CNS bacteria during the milking process.
- Teat Health Management: CNS bacteria are opportunistic pathogens that infect cows with compromised teat defences. Ensuring that cows have healthy, undamaged teats is critical for reducing infection risk. This includes:
- Emollients are used in post-milking teat dips to keep teats soft and supple, reducing the risk of cracks or sores where bacteria can enter.
- Minimising over-milking, which can damage teat ends and create entry points for bacteria.
- Selective Dry Cow Therapy: Dry cow therapy is an important tool for controlling mastitis during the dry period when cows are most vulnerable to infection. Selective dry cow therapy involves treating cows with a history of high SCC or mastitis infections with antibiotics at dry-off while using teat sealants for others. This can help clear existing infections and prevent new ones from taking hold.
- Regular Monitoring and Testing: Routine milk testing, particularly SCC monitoring and milk culturing, is essential for identifying subclinical infections before they become problematic. Farmers should work closely with their veterinarians or diagnostic labs to establish a testing schedule and consistently monitor udder health.
If you’re concerned about subclinical mastitis in your dairy herd, testing for coagulase-negative staphylococci is crucial to ensuring optimal milk production and cow health.
At FarmLab Diagnostics, we offer comprehensive milk testing services, including SCC testing and bacterial cultures, to help identify and manage CNS infections.