Milk Quality Effects of a High Somatic Cell Count

Milk quality starts on the farm, so dairy producers play an integral role in ensuring safe, wholesome dairy food products are available to consumers. One of the key quality indicators most producers monitor is the somatic cell counts (SCC). Many producers track SCC because of financial implications, including the potential loss of quality premiums or even loss of a milk market in cases of prolonged issues with high SCC. Others rely on SCC as a snapshot reflecting issues with herd health and their bottom line due to decreased production and treatment costs associated with mastitis.

Dairy processors also monitor the SCC of the milk they receive. While the current US legal maximum limit for bulk tank SCC for Grade A milk is 750,000 cells/mL, the national average is well below this level. Many dairy farms strive for an average SCC of less than 200,000 cells/mL, which is reflected by the national average. A lower SCC is advantageous to processors for many reasons. A higher SCC is tied to changes in milk composition, increased activity of detrimental enzymes, potential defects in finished products, and decreased shelf life. For this reason, many processors will not accept milk that exceeds a certain SCC level as dictated by their product standards. If processors receive milk with high SCC, they may have to incur additional costs as they may have to make adjustments in production to maximize the quality, consistency, yield, and other attributes of the finished products.

Sensory attributes such as flavor, taste, odor, or appearance can be affected by high SCC as well. Some consumers may be able to perceive these changes, which may alter their experience with the product. For example, rancidity is an off flavor that develops as milkfat is degraded into free fatty acids, and can be described as sour, unclean, or soap flavor (Dairy Practices Council, 2008). Other off-flavors linked to high SCC include a salty taste from cows that are later in their lactation or have mastitis, and bitterness due to the degradation of the protein by an enzyme.

At the cow level, an increase in SCC corresponds to an increase in leukocytes and other components of the cow's immune system that are responding to the infection. This leads to the release of enzymes in the milk that can alter components. Certain enzymes, known as lipases, are tied to changes in milkfat, while others, called proteases, result in changes in the protein (Gösta and Tetra Pak Processing Systems, 2015). Producers can appreciate the effects of enzymes on milkfat and protein since the amount of their milk check may be based on the amount of these components in their bulk tank. Some of the milk constituents connected to a high SCC, including fat, lactose, casein, potassium, and chloride decrease while others such as whey protein, lactoferrin, sodium, and chloride increase with a higher SCC (National Mastitis Council, 2016). These changes in constituents may require formulation adjustments on the part of the processor. The processor's ability to accommodate additional components such as whey protein may vary depending on the products being manufactured and their requirements.

Since we have established there is a connection between the presence of enzymes and the SCC, let's take a closer look at enzymes and how they get into milk. Enzymes are proteins that start chemical reactions, which, in this case, are the breakdown of dairy products. Some are naturally present in milk, while others are intentionally added during product manufacture, or they may be in milk due to the presence of certain microorganisms. For example, dairy producers know Staphylococcus aureus as a pathogen that causes contagious mastitis, but it also produces lipases.

The effects on milk quality according to the pathogen types by groups consisting of contagious, environmental, and opportunistic, were reported (Bobbo et al., 2017). Overall, no difference was reported between the groups of pathogens. However, the researchers concluded that SCC was an important indicator to monitor. While several other attributes of the milk were also examined, a longer coagulation time was observed with the subclinical cases of contagious pathogens because of a higher pH of the milk, lower amounts of lactose, and degradation of the casein. Culture-negative samples with a high SCC also demonstrated decreased milk quality.

By understanding the importance of a low SCC to the dairy processor, producers can recognize the added benefits and take steps to maintain or lower their herd's SCC. The results are beneficial for the udder health of their cows and their bottom line.

References

Bobbo T, Ruegg PL, Fiore E, Gianesella M, Morgante M, Pasotto D, Bittante G, and A Cecchinato. 2017. Associations between pathogen-specific cases of subclinical mastitis and cheese yield, quality, protein composition, and cheese-making traits in dairy cows. J Dairy Sci 100:4868-83.

Dairy Practices Council. 2008. GL 038: Guidelines for preventing off-flavors and rancid flavors in milk. 2nd rev. ed. Keyport, NJ.

Gösta, B and Tetra Pak Processing Systems AB (pub). 2015. Dairy processing handbook -3rd ed. Tetra Pak Systems AB, Lund, Sweden.

National Mastitis Council. 2016. Current concepts of bovine mastitis, 5th ed The National Mastitis Council, New Prague, MN.