Somatic cell count (SCC) is the total number of cells per milliliter of milk and is one of the main indicators of milk quality in dairy cows. Somatic cells are made of 2% mammary gland cells and around 98% white blood cells – leucocytes that are immune cells, produced by the cow’s immune system. As SCC are immune cells, the number found in the milk increases as a response to an immune challenge in the udder. This challenge is usually caused by pathogens and leads to inflammation. The most important factor affecting the SCC for an individual quarter, and eventually at herd level, is the mammary gland infection known as mastitis. Other factors involved in raising SCC are minor and insignificant compared to mastitis, so this allows us to use SCC as an indicator for subclinical mastitis. While mastitis is the most common and expensive disease in dairy farms, SCC gives us the opportunity to monitor subclinical cases on an individual and herd level using various SCC tests.
Mastitis is caused by a variety of microorganisms, the majority of which are bacteria that enter the mammary gland through the teat canal. Mastitis itself is inflammation of the mammary gland in response to the infection caused by these pathogens, and in rare cases, to chemical or metabolic factors. Appropriate immune function is essential for host defence against intramammary infections. The first and most common line of defence is the innate immune system, which triggers a proinflammatory response. It is a known fact that the mammary gland immune system is compromised during drying-off and around calving, the two periods representing the highest risk of mammary infection.
To stop the infection, additional immune cells migrate to the mammary gland, raising the SCC and reducing milk secretion due to increasing inflammation. The first immune cells that are recruited and migrate into the mammary gland are the neutrophils (PMNs), which form an important line of defence. The primary function of PMNs is to engulf, phagocytize, and destroy foreign material, including invading bacteria. In a perfect situation, the action of these neutrophils would eliminate the bacteria causing the infection. When the immune system is functioning properly, the problem should be rapidly resolved with a short and transient increase in SCC. However, this is not the case for most cows, especially around calving and drying-off, and during periods of stress, when the immune system is suppressed. In these cases, the number of mature neutrophils is limited and insufficient, but the bone marrow continues to produce large numbers of immature neutrophils that are mobilized to the inflammation.
Economic impact of somatic cell count on milk production
Somatic cells are not only a scientific concept, but they are also of great practical importance to farmers. High SCCs are related to a milk premium or penalty, and also directly affect milk production. SCC rises in response to mammary gland infection, causing inflammation and reducing the ability of the mammary gland tissue to produce milk.
These are obvious, clinical cases of mastitis that require treatment and special care but most mastitis is subclinical and goes undetected by the farmer, and may not be regarded as a potential economic loss.
We can use the SCC as an indicator to evaluate losses from subclinical mastitis. Most farmers will consider the SCC in a similar way to fat and protein, as a measurement for milk premium or penalty. However, many studies show that changes in SCC are related to economic losses that go far beyond the milk premium.
Several factors are affected by an increased SCC:
1. Reduction of milk production over the entire lactation
2. Increased risk of clinical mastitis
3. Increased culling rate due to SCC and mastitis
An increase in bulk milk SCC to over 100 000 affects milk production.
Relation between SCC and estimated loss of milk production
Similar numbers were produced by meta-analysis of a large number of reference studies from the USA, Canada, UK, Germany, and many other European countries. According to this meta-analysis, when bulk milk SCC is above 100 000, the farm loses about 3% of its milk production.
As well as reducing milk production, a high SCC increases the risk of clinical mastitis and related culling rates.
If we take into account the reduced milk production and increase in cases of clinical mastitis and culling rates, we can estimate that a farm with 100 cows and average yield of 8 000 kg/cow/year could actually gain around 4 000 Euros per year by reducing SCC by from 200 000 to 100 000, depending on milk price.
Investment in reducing SCC can increase dairy farm profitability. Several methods can be considered when building a strategy for SCC reduction.
It is recommended that cows with very high SCCs for a prolonged length of time are culled as they are more prone to clinical mastitis and fertility problems. However, culling should be carried out according to an established breeding program, and in collaboration with a vet.
Yeast postbiotic Safmannan helps maintain adequate immune system
Immune and non-immune cells from the host express at their cell surface several receptors so called PRR (Pathogen Recognition Receptors) able to recognise pathogens through certain molecular patterns. These molecular patterns, largely shared among microbes and pathogens, are called MAMPs (Microbial-Associated Molecular Patterns) or PAMPs (Pathogen-Associated Molecular Patterns) and are distinguishable from host molecules.
Safmannan shows ability to interact with the immune cells of the innate immune system as macrophages and dendritic cells situated in the gut and enhance their response to pathogen challenges, but also to improve the overall immune status of the animal. Recent publication in JDS (J. Dairy Sci. 103 https://doi.org/10.3168/jds.2019-17660)
Immune cells, activated by Safmannan respond faster and better in front of a challenge.
This activation of immune system helps the cow’s immune system fights more efficiently pathogen challenges which may lead also to reduction of SCC in dairy herds at risk.
Safmannan showed a superior immune response in-vitro from challenged monocytes in comparison with other yeast products even at 10 times lower dose.
Supplementing Safmannan to dairy cows in commercial farms helps lowering SCC as showed in numerous trials.
When Safmannan was supplemented to lactating dairy cows, it helped to reduce the SCC. Eight Dutch dairy farms that had been feeding Actisaf for a long time supplemented their cows with an additional 8g/c/d Safmannan for a trial period. Three milk samples were taken from each farm before Safmannan supplementation, and three samples after. The SCC decreased over the trial period, from an average of 280,000 per farm to below 200,000, which is considered the threshold for subclinical mastitis.
Data from field trial with over 1000 lactating cows from in 8 Dutch dairy farms. After Safmannan supplementation a reduction of SCC was observed.