Antibiotics affect the somatic cell count in milk by lowering these levels, especially when used as antibiotic dry cow therapy. The effect depends on the initial cell count and the timing of treatment.
- Cows with high somatic cell count before dry off face a greater risk of infection and culling.
- Dry cow therapy shows a 63.26% cure rate, and combining antibiotics with internal teat sealants can improve results.
| Dried Off Method | SCC at Calving | SCC at 14 Days in Milk |
|---|---|---|
| Without antibiotics | 772,000 | 46,000 |
| With antibiotics | 578,000 | 30,000 |
Farmers use tools like the California Mastitis Test or DeLaval cell counter to measure these changes. Understanding how antibiotics affect milk quality helps ensure both safety and productivity.
Key Takeaways
- Antibiotic dry cow therapy effectively lowers somatic cell counts by curing infections and preventing new ones, improving milk quality and udder health.
- Regular monitoring of somatic cell counts using testers helps farmers detect mastitis early and make informed treatment decisions.
- Antibiotics may not work well for chronic infections, so farmers should combine treatment with good management and consider culling persistently infected cows.
- Using antibiotics responsibly, following withdrawal times, and adopting selective treatments protect milk safety and reduce antibiotic resistance risks.
Somatic Cell Count in Milk
What Is Somatic Cell Count?
Somatic cell count in milk refers to the concentration of somatic cells, mainly white blood cells (leukocytes) and a smaller portion of epithelial cells, present in each milliliter of milk. These cells play a crucial role in the cow’s immune defense, especially when the udder faces infection.
- Somatic cell counts are measured as the number of cells per milliliter or sometimes converted to a logarithmic value.
- The presence of these cells signals the cow’s response to pathogens, such as those causing mastitis.
- Elevated somatic cell counts indicate inflammation or infection in the mammary gland, which can reduce milk yield and quality.
- Regulatory agencies, including those in the European Union, set limits for raw milk, often at or below 400,000 cells per milliliter.
- Dairy processors use somatic cell counts as a key quality parameter, rewarding farmers for lower counts.
| Milk Condition | Typical Somatic Cell Count (SCC) Range (cells/μL) | Mean SCC (cells/μL) | Notes |
|---|---|---|---|
| Healthy Milk | < 104 (some sources < 200) | ~187 | Based on visual health screening and infant health; aligns with International Dairy Federation guidelines |
| Mastitic Milk | > 500 (clinical mastitis), > 5000 (severe cases) | ~3604 | Clinical symptoms include breast engorgement, fever, redness, pus; SCC increases markedly during infection |
| Regulatory Thresholds | < 200 (non-mastitic), 500 (clinical mastitis), > 5000 (severe mastitis) | N/A | International Dairy Federation classification; milk with SCC > 400 (Europe) not for consumption; thresholds vary by region |
Why Somatic Cell Counts Matter?
Somatic cell counts serve as a vital indicator of udder health and milk quality.
High somatic cell counts in dairy cow usually signal an immune response to mastitis-causing bacteria. Healthy cows maintain counts below 200,000 cells per milliliter, while higher values suggest infection or inflammation.
A rise in somatic cell counts leads to several negative outcomes:
- Milk taste and shelf life decline, making it less suitable for products like cheese and yogurt.
- Milk with counts above 400,000 cells per milliliter is considered unfit for human consumption in many regions.
- Dairy farmers face financial penalties or rejection of high-count milk by processors.
- Monitoring somatic cell counts allows early detection of mastitis, helping farmers protect herd health and milk quality.
- High counts often mean lower milk yield, as infection damages milk-producing tissue.
High somatic cell counts also reflect the presence of pathogens such as Streptococcus uberis and Staphylococcus aureus, which can compromise milk safety. Increased enzyme activity from these cells can degrade milk proteins, leading to bitterness and reduced processing quality. Regulatory standards exist to protect consumers and ensure only safe, high-quality milk enters the food supply.
High Somatic Cell Counts and Milk Quality
Causes of High Somatic Cell Counts
Many factors can lead to high somatic cell counts in milk. The most common cause is infection by pathogens that invade the udder and trigger inflammation. These pathogens include both contagious bacteria, such as Staphylococcus aureus and Streptococcus agalactiae, and environmental bacteria like Streptococcus uberis and coliforms. The following table summarizes the main causes and their impact on somatic cell counts:
| Cause Category | Specific Factors / Examples | Explanation / Impact on SCC |
|---|---|---|
| Infection (Pathogens) | Contagious: Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae | These pathogens spread between cows during milking, causing mastitis and increasing SCC. |
| Environmental: Streptococcus uberis, Enterococcus spp., Arcanobacterium pyogenes, coagulase-negative Staphylococci, coliforms | Transmitted from environment (bedding, manure, soil) to mammary gland, leading to opportunistic infections and elevated SCC. | |
| Physiological Factors | Parity, Stage of lactation, Calving, Pregnancy | Older cows and certain lactation stages show higher SCC; calving and pregnancy are stressful physiological stages increasing SCC. |
| Body Condition Score | Higher BCS at calving linked to lower SCC in early parity cows but higher SCC in cows of third parity or more | Body condition and weight changes influence immune status and SCC levels. |
| Environmental Factors | Season, Temperature, Humidity | Heat and humidity increase stress and bacterial growth, raising SCC; seasonal variations affect SCC and milk quality. |
| Management Practices | Milking hygiene, Housing, Dry cow therapy, Nutrition | Proper management reduces SCC by preventing infections and stress; poor practices increase SCC. |
Pathogens such as Staphylococcus aureus, coagulase-negative staphylococci, and Streptococcus species cause intramammary infections that trigger inflammation. This process increases the number of somatic cells in milk. The severity of the response and the type of pathogen both influence how much the somatic cell counts rise.
Impact on Milk and Udder Health
High somatic cell counts have a direct effect on both milk quality and udder health. When somatic cell counts increase, milk production drops. Cows with counts above 1,000,000 cells/mL can lose up to 16.9% of their milk yield. The following table shows how different levels of somatic cell counts score affect milk production and composition:
| SCC Group (×10³ cells/mL) | Impact on Milk Yield | Impact on Milk Protein | Impact on Milk Lactose | Impact on Milk Fat | Impact on Total Solids | Notes |
|---|---|---|---|---|---|---|
| ≤ 200 | Baseline (highest yield) | Baseline | Baseline | No significant change | Baseline | Reference group |
| 201 – 500 | 1-4.6% decrease | Significant decrease | Decrease in 2nd lactation | No significant change | Increase | Subclinical mastitis range |
| 501 – 999 | 4.9-5.35% decrease | Significant decrease | Decrease in 2nd lactation | No significant change | Increase | Milk quality affected |
| ≥ 1000 | 10.4-16.9% decrease | Significant decrease | Decrease in 2nd lactation | No significant change | Increase | Marked production loss |
High somatic cell counts also change the composition of milk. Protein and total solids increase, but lactose drops, especially in cows with subclinical mastitis. Milk fat usually stays the same. These changes lower the quality of milk for processing and reduce its value.
Mastitis risk rises with high somatic cell counts. Older cows and those producing more than 10 liters per day face a greater chance of repeated mastitis episodes. Poor hygiene and damaged teat ends also increase the risk. High somatic cell counts signal ongoing or past infections, making mastitis more likely to recur and harming udder health. Farmers must monitor somatic cell counts closely to protect both milk production and animal well-being.
How Antibiotics Affect Somatic Cell Count?
Antibiotics and Dry Cow Therapy
Antibiotics affect somatic cell count in milk by targeting the bacteria that cause mastitis. During dry cow therapy, farmers administer antibiotic treatment at the end of lactation, before cows enter the dry period. This approach cures existing intramammary infections and prevents new ones from developing. Research shows that blanket dry cow therapy with intramammary antibiotics lowers contagious mastitis and reduces somatic cell counts internationally.
- Blanket therapy treats all cows, while selective therapy targets only those with infection.
- Studies report that cows receiving antibiotics plus internal teat sealants have lower infection rates and lower somatic cell counts after calving than those treated with sealants alone.
- Cows with higher milk yield at dry-off benefit most from combined antibiotic and sealant treatment.
Expert commentary highlights that cows with very low somatic cell counts at drying off face a higher risk of new infections during the dry period. Administering antibiotic dry cow therapy with an extended Gram-negative spectrum reduces clinical mastitis somatic cell count in the next lactation. Selective therapy requires careful identification of infected cows. Missing infections can result in persistent mastitis and higher somatic cell counts after calving.
Overall, antibiotic treatment during the dry period remains a key strategy for reducing somatic cell counts and improving udder health, especially in herds with contagious pathogens.
Effectiveness Based on Initial Somatic Cell Counts
The effectiveness of antibiotic treatment depends on the initial somatic cell count before dry-off. Studies show that cows with high somatic cell counts before drying off experience significant improvements after antibiotic dry cow therapy. Cure rates for cows with high initial counts reach up to 83% when managed by experienced staff. For cows with low initial counts, new infection rates remain low after treatment, regardless of who administers it.
Another study found that cows with at least one high somatic cell count or a high California Mastitis Test score during lactation benefit more from combined antibiotic and internal teat sealant treatment at dry-off. These cows show greater reductions in somatic cell counts and increased milk production compared to untreated cows.
However, research also suggests that antibiotic treatment outcomes do not differ significantly between cows with high and low initial somatic cell counts in terms of cure and new infection rates. This means that while cows with high somatic cell counts may see more dramatic improvements, all cows can benefit from proper treatment protocols.
During lactation, antibiotics affect somatic cell count less effectively in cows with high somatic cell counts. A large retrospective analysis found that antibiotic treatment at dry-off led to an average reduction of 1,500 cells/mL in the following lactation. However, antibiotic use during lactation did not significantly reduce the frequency of clinical mastitis in the first 90 days of milk production.
Pilot studies on cows with low somatic cell counts at dry-off found no significant differences in udder health or milk yield between those treated with antibiotics and those given only internal teat sealants. This supports the use of selective dry cow therapy, where only cows with high somatic cell counts or infection receive antibiotics, reducing unnecessary antibiotic exposure.
Monitoring with Somatic Cell Count Tester
Farmers use a somatic cell count tester to track changes in somatic cell counts after antibiotic treatment. The Dairy Herd Improvement (DHI) program provides an effective and affordable way to monitor individual cow somatic cell counts. By collecting milk samples every month or two, producers can observe trends over time.
Routine monitoring helps identify cows with chronically high somatic cell counts and assess the effectiveness of antibiotic treatment. DHI reports offer detailed profiles by lactation stage and historical data, allowing farmers to see how somatic cell counts respond to interventions.
Regular use of a somatic cell count tester enables early detection of mastitis somatic cell count, supports selective antibiotic use, and helps maintain milk quality.
Lactating cows with high somatic cell counts require close monitoring. Antibiotic treatment during lactation may not always lower somatic cell counts effectively, so ongoing testing is essential. By using a somatic cell count tester, farmers can make informed decisions about further treatment and management, ensuring both udder health and milk safety.
Limitations of Antibiotics for High Somatic Cell Counts
Cases Where Antibiotics May Not Work
Antibiotic treatment does not always lower somatic cell counts, especially in chronic or severe mastitis cases. Chronic Staphylococcus aureus infections often resist treatment because microabscesses and scar tissue block the antibiotic from reaching bacteria. Cows with long-term infections usually do not respond well to treatment and can continue to spread mastitis within the herd.
Management strategies such as culling or separating chronically infected cows play a key role in mastitis control programs.
The following table highlights common limitations:
| Limitation Aspect | Explanation |
|---|---|
| Poor efficacy in chronic infections | Antibiotics struggle to cure chronic mastitis due to blocked drug penetration. |
| Higher SCC in chronic cases | Chronic mastitis leads to higher somatic cell counts and poor response to treatment. |
| IMM vs systemic treatment | Intramammary treatment may result in higher post-treatment SCC, especially in older cows. |
| Timing and cow age effects | Early lactation and older cows respond less favorably to intramammary treatment. |
| Recommendation on culling | Culling is often better than treatment for chronic cases to prevent reinfection. |
| Risk of indiscriminate use | Indiscriminate antibiotic use can worsen infection and SCC problems. |
Antibiotic treatment works best for cows with recent infections. Prevention and good management remain essential for long-term mastitis control.
Antibiotic Resistance Concerns
Antibiotic resistance among mastitis-causing bacteria is a growing problem in dairy herds. Escherichia coli, which causes about 80% of coliform mastitis cases, often shows resistance to common drugs. Staphylococcus and Streptococcus species also frequently resist antibiotics like ampicillin, tetracycline, and neomycin.
Many bacteria carry multiple resistance genes, making treatment more difficult. Herds that use antibiotics indiscriminately see higher rates of resistance.
Prudent antimicrobial use helps slow the spread of resistance and keeps treatment options effective.
Studies show that when farms reduce antibiotic use, resistance among mastitis pathogens drops. This finding supports careful use of antibiotics as part of mastitis control programs.
Milk Withdrawal and Safety
After antibiotic treatment, milk may contain residues that pose health risks. Herds with high somatic cell counts, especially those above 700,000 cells/mL, have a much higher risk of antibiotic residue violations. These residues can cause allergies, toxicity, and contribute to antimicrobial resistance in people.
Maintaining low somatic cell counts helps reduce the risk of residues and ensures milk safety. The following table summarizes key findings:
| Aspect | Evidence Summary |
|---|---|
| Correlation between SCC and residues | Higher SCC links to more antibiotic residues in milk. |
| Health risks of residues | Residues above limits can cause allergies and toxicity. |
| SCC as a risk factor | Herds with SCC >700,000 cells/mL have 7 times higher risk of residue violations. |
| Importance of monitoring | Regular testing ensures milk quality and safety. |
Strict adherence to withdrawal periods is essential. The chart below shows recommended withdrawal times for common antibiotics:
Producers must follow these guidelines to keep milk free of residues and safe for consumers.
Practical Implications for Farmers and Consumers
Best Practices for Managing Somatic Cell Counts
Farmers can improve milk production and quality by adopting evidence-based prevention strategies tailored to their herds. Collaboration with veterinarians and animal scientists helps identify the most effective approaches for each farm. Careful documentation of antimicrobial treatments, with a focus on reducing the use of critically important drugs, supports responsible management. Selective Dry Cow Therapy (SDCT) targets only cows with a history of mastitis, high somatic cell counts, or high milk production. This targeted approach, supported by herd management software, reduces unnecessary antibiotic use while maintaining udder health and milk yield.
Routine monitoring of individual cows using a somatic cell count test kit allows for early detection of problems. Clean udders, larger management groups, and selective treatment of mastitis cases further lower somatic cell counts. Non-antibiotic interventions, such as probiotics, bacteriophages, and phytochemicals, have shown cure rates up to 85% and can reduce somatic cell counts by as much as 75%. These methods help maintain animal health, support sustainable production, and limit antimicrobial resistance.
Tip: Farmers who combine regular monitoring with targeted treatments and good hygiene practices see the greatest improvements in milk production and herd health.
Regulatory Standards for Milk
Regulatory agencies set limits on somatic cell count standards to ensure milk quality and safety. In the United States, the Grade “A” Pasteurized Milk Ordinance sets the limit at 750,000 cells per milliliter. Many advocacy groups push for a stricter limit of 400,000 cells/mL, which matches the European Union’s standard. The EU calculates compliance using a 3-month geometric mean and applies seasonal adjustments to account for natural variations in milk production.
Agencies monitor compliance by testing bulk tank somatic cell counts in milk shipments. In the U.S., repeated violations can lead to penalties or suspension of the right to sell Grade A milk. The EU uses rolling averages and statistical evaluations to ensure ongoing compliance. These standards encourage farmers to adopt better management practices and maintain high-quality milk production.
Using a Somatic Cell Count Tester
A somatic cell count tester gives farmers rapid, on-farm results for monitoring udder health and milk quality. Devices like the DeLaval Cell Counter provide accurate readings that match laboratory standards. The California Mastitis Test also performs well for detecting subclinical mastitis. Farmers should follow recommended sample handling procedures, as temperature can affect test accuracy.
On-farm testers allow for frequent checks—ideally daily or multiple times per day. This frequent monitoring helps detect spikes in somatic cell counts quickly, enabling prompt action to protect milk production. Automated systems, such as the online California Mastitis Test, make it easier to track trends and respond to changes in herd health. By using a somatic cell counter for milk regularly, farmers can maintain optimal milk production and reduce the risk of mastitis.
Conclusion
Recent studies confirm that antibiotics, especially when used as dry cow therapy, lower somatic cell counts in milk. Selective dry cow therapy guided by SCC thresholds maintains udder health and reduces unnecessary antibiotic use. Regular monitoring with a somatic cell count tester helps farmers track udder health and make informed decisions. Responsible antibiotic use, including adherence to withdrawal periods, protects milk safety and public health.
Farmers and consumers benefit most when they combine SCC monitoring, targeted treatments, and strict safety practices.
FAQ
What Is the Best Time to Use Antibiotics for Lowering Somatic Cell Count?
The best time for antibiotic treatment is during dry cow therapy, right after the last milking of lactation. This timing helps cure existing infections and prevents new ones, leading to lower somatic cell counts after calving.
Can Farmers Use Somatic Cell Count Testers at Home?
Yes, farmers can use portable somatic cell count testers on the farm. These devices provide quick results and help monitor udder health. Regular testing allows early detection of mastitis and supports better milk quality management.
Do Antibiotics Always Work for High Somatic Cell Counts?
No, antibiotics do not always work for high somatic cell counts, especially in chronic mastitis cases. Some infections resist treatment. Farmers may need to cull cows with persistent high counts to protect herd health.
How Long Should Milk Be Withheld After Antibiotic Treatment?
Milk must be withheld for a specific withdrawal period after antibiotic use. This period varies by drug, usually ranging from 2 to 7 days. Farmers should always follow label instructions to ensure milk safety.
Are There Alternatives to Antibiotics for Reducing Somatic Cell Counts?
Yes, alternatives include improved hygiene, probiotics, and selective dry cow therapy. Some farms use bacteriophages or herbal treatments. These methods can help lower somatic cell counts and reduce antibiotic use.