Somatic cell count serves as a vital indicator for milk quality and cow health in dairy cows. Recent studies reveal that average somatic cell count in dairy cows rises during seasonal transitions, with higher levels observed in summer and autumn. Elevated somatic cell count often signals mastitis, which reduces milk yield and alters milk composition. Dairy farmers utilize somatic cell count tester to track herd somatic cell count, manage cow health, and address seasonal fluctuations. Reliable monitoring helps maintain average somatic cell count dairy cows at optimal levels, supporting both farm profitability and herd well-being.
Key Takeaways
Somatic cell count rises in dairy cows during summer and autumn due to heat stress, increasing the risk of mastitis and lowering milk quality.
Regular monitoring of somatic cell count helps farmers detect infections early and maintain healthy herds and good milk production.
Effective management practices like keeping bedding clean, cooling cows, and controlling flies reduce somatic cell count and prevent infections.
Breed, age, and lactation stage affect somatic cell count; older cows and certain breeds show higher counts and need closer attention.
Adjusting somatic cell count thresholds and management strategies by season and region improves milk quality and herd health year-round.
Average Somatic Cell Count in Dairy Cows: Seasonal Patterns
Yearly SCC Trends
Average somatic cell count in dairy cows display distinct yearly trends shaped by environmental and physiological factors. Researchers observe that milk somatic cell counts remain relatively stable across years, with most variability attributed to differences between farms rather than annual changes. For example, a Finnish longitudinal study found that average somatic cell count in dairy cows did not fluctuate significantly from year to year, regardless of dry cow therapy approaches. However, the proportion of cows with low somatic cell count decreases as lactation progresses. The following table illustrates this trend:
Days in Milk (DIM)
≤60
61–120
121–180
181–240
>240
% of cows with low SCC (≤50,000 cells/mL)
43.3%
41.3%
31.8%
28.4%
16.3%
% of cows with high SCC (>50,000 cells/mL)
56.7%
58.7%
68.2%
71.6%
83.7%
Longitudinal data from the UK national dairy herd between 2014 and 2023 reveal a significant improvement in milk somatic cell counts. The percentage of cows dried-off with no SCC recordings at or above 200,000 cells/ml increased from 39.7% in 2014 to 51.0% in 2023. This improvement reflects enhanced management practices and greater awareness of milk quality standards.
High and Low SCC Months
Seasonal fluctuations in average somatic cell count in dairy cows become most apparent when examining monthly data. National and regional reports consistently show that somatic cell counts peak during the summer months, especially August, and reach their lowest levels in winter, particularly December. For instance, a study in northeastern Iran reported that milk somatic cell counts in dairy cows peaked in August at 4.23 log10 cells/mL and dropped to 3.48 log10 cells/mL in December. These differences are statistically significant and highlight the impact of seasonal effects on milk composition and milk quality.
Dairy cows experience significant increases in somatic cell count during hot and humid months. Heat stress, measured by the temperature-humidity index, impairs immune function and increases the risk of mastitis. Published research shows that when the temperature-humidity index exceeds 68, cows suffer from heat stress, leading to elevated milk somatic cell counts and reduced milk production. Cows calving in warmer months have higher odds of mastitis and increased somatic cell counts compared to those calving in cooler months.
The following table summarizes typical seasonal patterns in somatic cell count:
Season
SCC Pattern Description
Indoor (Spring)
Lowest SCC levels observed, representing the baseline indoor period with generally better udder health.
Pasture (Summer)
Marked increase in SCC, often more than double the spring levels, attributed to both non-infectious factors and increased intramammary infections due to higher temperature and humidity. This increase occurs rapidly after pasture turnout.
Indoor (Fall)
Intermediate SCC levels, higher than spring but lower than summer, corresponding to late lactation period.
Regional Differences
Regional differences in average somatic cell count in dairy cows arise from a combination of environmental, genetic, and management factors. The following table outlines key contributors to regional variability in milk somatic cell counts and milk composition:
Factor
Description
Impact on Somatic Cell Count (SCC) and Differential SCC (DSCC)
Seasonal Variation
SCC and DSCC increase notably during summer due to heat stress impairing mammary defense mechanisms.
Higher SCC and DSCC in summer; DSCC more sensitive to seasonal changes than LSCC. Increased immune cells (PMN+lymphocytes) in milk during summer.
Breed Differences
Holstein-Friesian and Simmental breeds show similar seasonal trends but differ in magnitude.
Both breeds peak in SCC and DSCC during summer; differences attributed to phenotypic and genetic factors.
Herd Productivity Level
Herds with higher milk production levels tend to have lower SCC and DSCC values.
High productivity herds show lower somatic cells/mL but higher daily somatic cell counts due to greater milk yield; thresholds should consider milk yield.
Milking System & Parity
Milking type and parity influence SCC and DSCC variability, especially in older cows and automated milking.
Interactions affect SCC/DSCC trends during lactation; important for setting accurate inflammation thresholds.
Individual Cow Effect
Individual animal has greater influence on SCC and DSCC variability than herd factors.
Suggests genetic and phenotypic differences among cows are key contributors to SCC variability.
Environmental factors such as heat stress, barn hygiene, and microclimatic conditions play a significant role in regional differences. For example, cows housed in dirty or wet environments show higher milk somatic cell counts. The temperature-humidity index remains a significant association with seasonal increases in somatic cell count, especially during summer. Herds with higher daily milk production often maintain lower bulk milk scc values, but their total daily milk production results in higher daily somatic cell counts.
Tip: Dairy farmers should adjust milk somatic cell count thresholds for milk quality control based on seasonal effects and regional conditions. Regular monitoring of bulk milk somatic cell count helps identify significant associations between environmental stressors and milk composition.
Temperature and humidity play a significant role in shaping somatic cell count in milk throughout the year. The temperature-humidity index directly influences the risk of infection and clinical mastitis. When the temperature-humidity index rises, cows experience heat stress, which suppresses immune function and increases susceptibility to bacterial infection. This leads to a significant increase in somatic cell count, especially during summer. In contrast, cooler temperatures and lower humidity in winter result in the lowest somatic cell counts and improved milk composition.
The following table summarizes the effects of environmental changes on somatic cell count, milk composition, and microbial load:
Environmental Factor
Change Range
Effect on Somatic Cell Count (SCC)
Effect on Milk Components
Effect on Microbial Count
Temperature
6.2 °C to 31.3 °C
SCC decreased by ~16.8%
Protein, fat, SNF decreased by 4.09%, 5.75%, 1.31% respectively
Microbial count increased by ~13.7%
Humidity
54% to 82%
SCC increased by ~10.2%
Protein, fat, SNF increased by 3.61%, 4.84%, 1.06% respectively
Microbial count decreased by ~16.3%
Higher temperature-humidity index values in summer cause a significant rise in somatic cell counts and clinical mastitis cases. Milk somatic cells increase as cows struggle to maintain immune defenses under heat stress. The chart below illustrates how temperature and humidity changes affect somatic cell count in dairy cows:
Seasonal effects become most pronounced in summer, when the temperature-humidity index peaks. During this period, infection risk rises, and milk production often declines. In winter, the temperature-humidity index remains low, resulting in the lowest somatic cell counts and the best milk quality indicators. The table below highlights these seasonal patterns:
Season
Temperature-Humidity Index (THI)
Somatic Cell Count (SCC)
Milk Quality Indicators
Key Observations
Winter
Low THI
Lowest SCC
Highest milk yield, fat, protein, solids-not-fat (SNF), and pH
Cooler temperatures and lower humidity correlate with better udder health and milk quality
Summer
High THI
Highest SCC
Lower milk quality, increased microbial load
Elevated heat and humidity increase heat stress, leading to higher SCC and mastitis risk
Note: Dairy management teams should monitor the temperature-humidity index closely during summer. Early intervention can prevent significant increases in somatic cell count and reduce the risk of clinical mastitis.
Management Practices
Effective management practices significantly reduce somatic cell counts and the risk of infection in dairy cows, especially during high-risk seasons. Heat stress in summer increases environmental bacteria and suppresses immune function, leading to more clinical mastitis cases and high somatic cell count. Dairy management strategies focus on minimizing these risks through targeted interventions.
Cleaning teat ends with surgical spirit before dry cow treatment to lower infection rates.
Reducing stocking density during housing to decrease environmental bacteria and infection risk.
Increasing lying space per cow (10–12.5 m²) to improve comfort and reduce clinical mastitis.
Managing pasture rotation and minimizing time until first fore-milking after calving to lower somatic cell count.
Implementing selective dry cow therapy based on somatic cell counts and differential cell counts to reduce antimicrobial use without increasing infection risk.
Continuous monitoring of herd somatic cell count trends allows dairy management teams to detect significant increases or decreases over time. This proactive approach supports mastitis prevention and maintains optimal milk production and milk composition throughout the year.
Pasture vs. Indoor Housing
The choice between pasture and indoor housing does not show a significant effect on somatic cell count in dairy cows across seasons. Studies comparing cows housed indoors with those given free-choice pasture access during the dry period found no significant difference in somatic cell counts or infection rates. Both housing types resulted in similar average somatic cell counts, indicating that other factors, such as temperature-humidity index, management practices, and hygiene, play a more critical role in controlling infection and clinical mastitis.
Housing Type
Somatic Cell Count (SCC, 1,000 cells/mL)
Statistical Significance (P-value)
Indoor only (CTRL)
287 ± 101
0.81 (no significant difference)
Free-choice pasture access
289 ± 82
0.81 (no significant difference)
Tip: Dairy management should prioritize infection control, hygiene, and monitoring of the temperature-humidity index over housing type when aiming to reduce somatic cell counts and clinical mastitis risk.
Seasonal effects on somatic cell count depend more on environmental conditions and management than on whether cows remain indoors or graze on pasture. Maintaining high standards of hygiene, monitoring milk somatic cells, and adapting management practices to seasonal changes remain the most effective strategies for controlling infection, improving milk composition, and supporting daily milk production in dairy cows.
Breed, Parity, and Somatic Cell Counts
Breed Differences
Breed plays a crucial role in determining somatic cell count patterns and the risk of clinical mastitis in dairy herds. Holstein Friesian cows show the highest somatic cell count during summer, with a relatively stable baseline across other seasons. Simmental cows follow a similar seasonal trend but maintain lower somatic cell counts and experience fewer cases of clinical mastitis. Montbéliarde, Abondance, and Brown Swiss breeds generally have lower somatic cell counts and reduced clinical mastitis incidence compared to Holsteins. Genetic factors and innate immunity contribute to these differences, influencing how each breed responds to infection and environmental stress.
Breed(s)
Seasonal SCC Pattern
Seasonal DSCC Pattern
Breed Differences in SCC and Mastitis Incidence
Notes on Immune Response and Genetics
Holstein Friesian (HF)
Highest SCC in summer; LSCC relatively stable across seasons
DSCC peaks in summer (67.8%), lowest in winter (62.3%)
Higher SCC and mastitis incidence compared to some other breeds
Similar seasonal SCC trend as HF; highest in summer
DSCC shows pronounced seasonal variation, similar to HF
Lower SCC and mastitis incidence than Holsteins
Phenotypic and genetic differences affect SCC and immune cell production
Montbéliarde, Abondance, Brown Swiss
Not specified seasonally, but generally lower SCC and fewer clinical mastitis cases
N/A
Lower SCC and mastitis incidence than Holsteins
Genetic factors likely contribute to these differences
Canadian breeds (Holsteins, Ayrshires, Jerseys)
All show higher SCC in July-September; Jerseys also elevated in May-June
N/A
Jerseys show unique early summer SCC elevation
Seasonal SCC influenced by temperature and humidity; udder health programs vary by season
DSCC, or differential somatic cell count, provides a more sensitive indicator of seasonal changes than total SCC. Heat stress in summer increases both SCC and immune cell populations in milk, especially in Holsteins.
Studies on Canadian dairy breeds confirm that all breeds experience elevated somatic cell counts during summer months, with Jerseys showing a unique early summer increase. These findings highlight a significant association between breed, season, and the risk of infection. Breeds with lower somatic cell counts tend to have fewer cases of clinical mastitis, likely due to genetic resistance to infection and differences in immune response to bacteria.
Parity and Age Effects
Parity and age also influence somatic cell count and the risk of infection in dairy cows. Older cows, especially those over eight years, have significantly higher somatic cell counts than younger cows. Cows with five or more parities show both higher somatic cell counts and a greater prevalence of intramammary infection, reaching nearly 46%. The stage of lactation further affects these outcomes. Somatic cell count rises as lactation progresses, with late-lactation cows showing the highest values. Early lactation cows, particularly within the first week, face a 100% rate of intramammary infection, making them highly susceptible to clinical mastitis.
Factor
Effect on Somatic Cell Count (SCC) and Intramammary Infection (IMI)
Age
Older cows (>8 years) have significantly higher SCC than younger cows (≤4 years).
Parity
Cows with ≥5 parities show significantly higher SCC and higher IMI prevalence (~45.8%) than cows with fewer parities (1–2).
Lactation Stage
SCC increases with lactation stage, especially in late lactation (>60 days). Early lactation cows (≤7 days) have higher IMI rates (100%).
Mammary Quarter Location
Rear quarters have higher SCC and IMI prevalence than front quarters.
Seasonal Influence
Seasonal effects on SCC in relation to age or parity are not explicitly detailed in the study.
Dairy managers should monitor older cows and those with multiple parities more closely for infection and clinical mastitis, especially during late lactation. Rear quarters require extra attention, as they show higher somatic cell counts and infection rates. Bacteria thrive in these conditions, increasing the risk of clinical mastitis and reducing milk quality.
Monitoring and Managing SCC
Using Somatic Cell Count Tester
Routine monitoring of somatic cell count remains essential for early detection of clinical mastitis and infection in dairy herds. Monthly testing provides a practical approach, allowing dairy management teams to identify cows with rising somatic cell count and intervene before milk production declines. The somatic cell count tester offers reliable results, especially when used with a threshold of 100,000 cells/mL, which distinguishes healthy cows from those at risk of infection. Seasonal changes influence individual cow’s scc, so interpreting results requires attention to the time of year and lactation stage. During the immediate postpartum period, higher thresholds may be necessary due to naturally elevated somatic cell count in transition milk. Automated milking systems and online monitoring tools further support herd somatic cell count management by enabling real-time detection of udder health problems.
Preventive Strategies
Effective mastitis prevention relies on maintaining low somatic cell count through targeted management practices. Clean environments, proper hygiene, and selective antimicrobial use during the dry period reduce infection risk and support milk production. The following table summarizes strategies that decrease the likelihood of new high somatic cell count during vulnerable periods:
Preventive Strategy
Impact on New High SCC During Dry Period
Reduction of milk yield before dry-off
Decreases risk
Teat dip or spray after drying off
Decreases risk
Selective antimicrobial use
Decreases risk
Good hygiene during dry-off
Decreases risk
Cubicle housing for dry cows
Decreases risk
Consistent application of these strategies helps prevent clinical mastitis and infection, especially when cows face stress or immune suppression.
Nutrition and Cow Comfort
Cow comfort and nutrition play a vital role in controlling somatic cell count and supporting milk production. Comfortable stalls encourage cows to lie down, reducing lameness and health issues that can lead to infection and clinical mastitis. Bedding must remain dry and provide temperature regulation, especially during extreme weather. Heat stress increases somatic cell count by weakening immune response and promoting pathogen growth. Dairy management teams should provide shade, fans, and cooling systems to maintain cow comfort and reduce mastitis risk. Adjusting nutrition with antioxidants and electrolytes helps stabilize cows during periods of heat stress, supporting udder health and milk production.
Tip: Continuous monitoring, seasonal adjustment of thresholds, and proactive interventions ensure optimal herd somatic cell count and milk quality throughout the year.
Conclusion
Seasonal fluctuations in somatic cell count directly affect milk quality and herd health. Research shows that elevated SCC during summer reduces milk yield and alters milk quality components. Dairy farmers can improve milk quality by monitoring SCC trends, implementing proactive management, and adjusting practices for seasonal changes. Recommended steps include maintaining clean bedding, using milk diagnostics, and segregating high-SCC cows. Continuous monitoring and early intervention help sustain milk quality and protect herd health throughout the year.
Seasonal SCC changes impact milk quality by altering protein, lactose, and minerals.
Ongoing monitoring and proactive intervention are essential for optimal milk quality.
Industry guidelines emphasize environmental management and milking hygiene to maintain milk quality.
FAQ
What Is Considered a High Somatic Cell Count in Dairy Cows?
A somatic cell count above 200,000 cells/mL signals a high risk of mastitis. Most industry guidelines recommend maintaining bulk tank SCC below this threshold to ensure optimal milk quality and herd health.
How Often Should Dairy Farmers Test Somatic Cell Count?
Dairy farmers should test somatic cell count at least once per month. More frequent testing during high-risk seasons, such as summer, helps detect problems early and supports timely intervention.
Does Somatic Cell Count Affect Milk Quality?
Yes. Elevated somatic cell count reduces milk yield and alters milk composition. High SCC can increase bacterial counts and lower protein and lactose content, which impacts milk processing and product quality.
Can Nutrition Influence Somatic Cell Count?
Proper nutrition supports immune function and udder health. Diets rich in antioxidants, vitamins, and minerals help cows resist infection, which keeps somatic cell count within healthy limits.
Why Do Somatic Cell Counts Rise in Summer?
Heat stress during summer weakens immune defenses and increases bacterial growth. This leads to more mastitis cases and higher somatic cell counts. Farmers should monitor cows closely and use cooling strategies during hot months.
