Other Management Articles
- Building A Herd of High-Producing, Healthy Cows with Low Involuntary Culling
- Culling Heifers: When and Why and the Impact on Herd Economics
- Economics Matter in Culling Decisions
- What is an ideal BCS at calving?
- Facts about Somatic Cell Counts
- First Layer of Defense Against Mastitis
- The When and Why of Milking Procedures
- Are Mastitis Vaccines a “Cure All”?
- Growing Heifers to Be Your Best Cows
- A Look in the Mirror
- Fertility Potential: The Bull + The Cow + The Inseminator + The Environment
Somatic Cell Count is important to all aspects of our industry. Somatic cells reside within milk as an integral part of the cow’s immune system. Somatic Cell Counts (SCC) are quantified as the number of cells per mL of milk. Lower SCC means extended product shelf life for processors. Consumers have found that milk with lower SCC has improved flavor. Dairy managers spend less on treatments of lower SCC cows and cows with lower SCC tend to have longer healthier lives.
The term somatic means “of the body” and somatic cells are a normal part of milk. Somatic cells are a combination of cells lining the udder tissue (epithelial) and white blood cells. The epithelial lining cells are shed from the alveoli and milk ducts, allowing regeneration of the full production ability of the milk glands. The white blood cells move from the blood into the udder in between junctions of the blood vessels and udder tissue. The white blood cells in an uninfected cow are primarily lymphocytes (66%) with neutrophils as the next predominate cell (19%). These are the second layer of defense in the udder, beyond the protective mechanisms of the teat. Both the epithelial cells and the white blood cells are triggered by pathogens that enter the udder. The cow’s immune system utilizes these cells and their response to remove infectious agents. This is achieved both by stimulating the creation and influx of immunoglobins to bind cells and by attracting neutrophils into the udder to eat (phagocytosis) pathogens. This changes the white blood cell population of milk so that Neutrophils dominate as 75% of the SCC, while lymphocytes are reduced to 17%. Generally, a cow is considered to have an infected quarter if her SCC is greater than 200,000 cells per mL.
To some degree, it is unfortunate that the initial reaction of the somatic cells is to create inflammation. The epithelial and leukocyte cells release chemicals that trigger a cascade of inflammatory events that start the immunoglobin production process but also loosen the junctions between cells so that it is easier for the neutrophils to leave the blood vessels and enter the milk. This inflammatory response is needed to stop the infection, but an overzealous response also delays a return to normal milk, damaging tissue and health. Most of the redness, swelling and pain are related to the cow’s response to infection rather than the invading agents. Because of these loosened junctions, other blood particles flow into the udder. The milk becomes more like the serum, with changes in color, salinity, and even the protein in the milk becomes more similar to blood proteins. This explains some of the changes we observe in taste characteristics of high SCC milk.
There is much “common knowledge” on somatic cells. Which are truth and which are myth?
Older cows naturally have higher SCC.
Myth – non infected cows show little difference in SCC between lactations.
Cows showing estrus will have higher SCC.
Myth – Estrus has no significant effect on SCC.
SCC varies by days in milk.
Truth – SCC is highest post calving and reaches a low point between 25 and 45 DIM, slowly rising as milk production decreases.
Heat stress increases SCC.
Truth and Myth – There is a slight shift in SCC during stressful periods that tends to follow feed intake patterns. Is this a true change in SCC?
During a milking SCC will change.
Truth – SCC is highest in prestriping but lowest in early milk.
An infected cow will consistently show high SCC.
Myth – SCC in infected quarters tends to fluctuate.
Systemic antibiotics (injectable) are a good way to assist the body’s response in clearing mastitis from the udder.
Truth and Myth – Because antibiotics must filter through the tight junctions it is hard to get high levels of antibiotics in the udder by injection. Intramammary antibiotics put a high concentration of antibiotic where the infection is growing. Sometimes the infection can move from the udder into the body (septicemia), so injectable antibiotics may help in these extremely sick cows.
Chronic high SCC arises from damage to the udder.
Myth – Although damage will allow leakage of blood fluids into the udder, neutrophils are drawn to the udder by signals given off in response to infection. Sometimes this infection is “walled off” and no longer in contact with the immune system, which may be part of the reason behind SCC fluctuation in infected cows
Body condition scores are related to high SCC.
Truth and Myth – Although not related directly to infection, both low BCS and high BCS cows have impaired energy processing which impacts the immune system. The result can allow infections to gain a foot hold. Both low and high BCS are mildly associated with high SCC
Somatic cells also have impacts on other areas of the cow. SCC is a biological response that takes energy to maintain. This energy comes from the cow and the cow’s response is lower production. Prostaglandins are part of the inflammatory response and prostaglandins are not good for maintaining pregnancy. Reproduction is impaired by the higher level of circulating prostaglandins, lower available energy and sometimes luteolytic circulating toxins from the mastitis. Energy that is diverted from production to health is one reason for lower milk yields. The combination of inflammatory response and toxins also decrease appetite, which reduces milk production. The infection and the immune response results in destruction of epithelial cells and replacement with scar tissue, reducing future production. These factors together impact production and reproduction, resulting in higher culling.
Here are highlights (or maybe low lights) from research on real world farms:
Doubling of the SCC resulted in over 1 kg decrease in daily production.
Increase of 17 days open with herds over 200,000.
20% lower conception for SCC over 200,000 during breeding to pregnancy diagnosis.
35% lower conception for clinical mastitis during breeding to pregnancy diagnosis.
Double the rate of early abortion for cows with mastitis and body condition of <2.75 compared to cows with BCS >2.75.
6% more income from the best 25% SCC cows in the herd compared to those in the third quartile (not even the worst).
Cows with over 200,000 SCC are 2.5 times more likely to develop a clinical case of mastitis by 60 days in milk.
Cows above 200,000 SCC are three times more likely to be culled within the first 60 DIM when compared with unaffected cows.
Somatic cells are an import part of a cow’s protection from one of the industry’s most devastating management diseases: mastitis. Understanding and measuring the Somatic Cell Count can give us clues to how our management is performing and should inspire management decisions for both short-term solutions and long-term decisions.
The Genetic Connection
Understanding the connection between SCC and cow health, combined with genetic selection for reduced Somatic Cell Score (SCS) and increased resistance to mastitis (Zoetis and CDCB Mastitis) will enable dairy producers to realize the full benefits of healthy cows and maximum milk quality.