**3. Somatic cell counts (SCC)**

Throughout the world in the last ten years, udder health programs have been increasing (Godkin *et al*., 1999; Østerås *et al.*, 1998; Plym 1996a; Plym et *al.*, 1996b; Sargeant *et al.*, 1998), and regarded as a critical production issue on dairy farms. In Europe, the European Economic Community (EEC) since 1998 does not recommend consumption of milk with SCC over 400, 000 cells/ml. In North America the limit has been established at 750, 000 (USA) and in Canada at 500, 000 cells (Sargeant *et al.*, 1998).

Somatic cells are, in great quantity, cells of the immune system (80% in uninfected quarters, and 99% in quarters with mastitis) (Sordillo *et al.*, 1997). They are part of the natural defense mechanisms, including lymphocytes, macrophages, polymorphonuclear and some epithelial cells (Pillai *et al*., 2001). Somatic cells are therefore a reflection of the inflammatory response to an IMI. Somatic cell counts are often used to distinguish between infected and uninfected quarters according to the general agreement between infection status and the inflammatory response to infection reflected as an increased SCC. As with any diagnostic test, errors will occur when solely depending on a single test. To minimize error, diagnostic test parameters such as sensitivity & specificity are calculated at various cut-off values in the continuum SCC (Schepers *et al*., 1997). In North America and Europe the SCC for an uninfected quarter is approximately 70, 000 cells. There is of course variation around this mean; its value can increase with age, decreasing milk production and days in milk period (Schepers *et al*., 1997). Hence, to be able to distinguish between infected and uninfected quarters a cut-off of approximately 200, 000 to 250, 000 cells is accepted (Dohoo *et al*., 1991; Laevens *et al.*, 1997; Leslie *et al*, 1997; Schepers *et al*, 1997). At this cut-off value, diagnostic sensitivity is approximately 75%, and specificity approximately 90% (Schepers *et al*., 1997). The 200, 000 cells cut-off is not considered a physiological cell concentration in milk able to distinguish between healthy and unhealthy udders, but it is a practical value under field conditions (minimizing diagnostic error). Erskine *et al.* 1987, evaluated 32 dairy herds, 16 with low SCC less than or equal to 150, 000 cells/ml and 16 with high SCC greater than or equal to 700, 000 cells/ml. From the 16 herds with low SCC, S. *agalactiae* was isolated in two herds (12.5%), and *S. aureus* was isolated from seven herds (44%). Moreover both microorganisms were found in all of the herds with high SCC, a program of post-milking teat dipping and treatment of all cows at the beginning of the non-lactating period was practiced in the herds with low SCC. Whist *et al*. (2007) reported low SCC in milk from heifers having *Streptococcus dysgalactiae* IMI and in noninfected glands the results indicated that SCC were high (between 50,000 and 100,000 cells/ml) during the immediate postpartum period, within the next 5 days after calving.

## **4. Bulk tank milk (BTM) SCC**

364 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

*coli* had a prevalence of 12.8% and 6.8 % respectively.

(USA) and in Canada at 500, 000 cells (Sargeant *et al.*, 1998).

**3. Somatic cell counts (SCC)** 

low effect on the mastitis caused by *Streptococcus* spp, catalase-negative cocci, and by environmental coliform bacteria which affect the udder. Among *Streptococcus* spp, *Streptococcus uberis* (*S. uberis*) is the most frequent as bovine udder pathogen (Olde Riekerink *et al.*, 2008). Moreover, the dairy environment is a determinant factor for mastitis development due to *S. uberis* and *Streptococcus dysgalactiae* subsp. *dysgalactiae (S. dysgalactiae*), and stabled dairies are in greater risk than those held in open pastures (NMC, 1999). Other *Streptococcus* spp related in lesser amount to bovine mastitis are *Streptococcus parauberis* (*S. parauberis*), *Streptococcus salivarius* (*S. salivarius*), and *Streptococcus sanguinis* (*S. sanguinis*) (Whitman, 2009). Some Enterococcus such as *Enterococcus faecium* (*E. faecium*), *Enterococcus faecalis* (*E. faecalis*), *Enterococcus saccharolyticus* (*E. saccharolyticus*) (Østerås, *et al*., 2006). *Aerococcus viridans* (*A. viridans*) has been also related to mastitis but its role has not been elucidated yet (Devriese *et al*., 1999; Zadoks *et al*., 2004). In Hungary, Jánosi1 and Baltay, (2004) determined that the environmental caused mastitis by *Streptococcus* sp and *E.* 

The environmental pathogens, by themselves, are not enough frequent and persistent to cause mastitis or as a significant elevation of somatic cells counts (SCC) of bulk milk (values over 400,000 cells/ml). However, 66% of mastitis caused by environmental *Streptococci* and 85% of those caused by coliform bacteria, display clinical presentation. Therefore, losses due to this type of mastitis can reach substantial amounts even in herds with low SCC (<300,000 cells/ml), mainly due to a high incidence of clinical mastitis as it has been estimated around a 46% of clinical mastitis per year in herds with bulk milk SCC counts of less than 200,000 cells/ml

Throughout the world in the last ten years, udder health programs have been increasing (Godkin *et al*., 1999; Østerås *et al.*, 1998; Plym 1996a; Plym et *al.*, 1996b; Sargeant *et al.*, 1998), and regarded as a critical production issue on dairy farms. In Europe, the European Economic Community (EEC) since 1998 does not recommend consumption of milk with SCC over 400, 000 cells/ml. In North America the limit has been established at 750, 000

Somatic cells are, in great quantity, cells of the immune system (80% in uninfected quarters, and 99% in quarters with mastitis) (Sordillo *et al.*, 1997). They are part of the natural defense mechanisms, including lymphocytes, macrophages, polymorphonuclear and some epithelial cells (Pillai *et al*., 2001). Somatic cells are therefore a reflection of the inflammatory response to an IMI. Somatic cell counts are often used to distinguish between infected and uninfected quarters according to the general agreement between infection status and the inflammatory response to infection reflected as an increased SCC. As with any diagnostic test, errors will occur when solely depending on a single test. To minimize error, diagnostic test parameters such as sensitivity & specificity are calculated at various cut-off values in the continuum SCC (Schepers *et al*., 1997). In North America and Europe the SCC for an uninfected quarter is approximately 70, 000 cells. There is of course variation around this mean; its value can increase with age, decreasing milk production and days in milk period (Schepers *et al*., 1997). BTM SCC is a general indicator of the udder health in a herd and it is also regarded as an indirect measure of milk quality (Schukken *et al.* 2003). Elevated SCC, are correlated with changes in milk composition, casein and more serum-derived whey proteins, as well as increased proteolytic and lipolytic activities (Auldist & Hubble, 1998). SCC may, however, vary greatly depending on factors such as number of lactations, stage of lactation, season and milking frequency (Harmon, 1994; Pyörälä, 2003). In BTM, where the total volume of milk will dilute effects from affected quarters, SCC appears to be less sensitive and specific as a biomarker for milk quality, e.g. suitability for cheese production (Leitner *et al.,* 2006).

Bulk tank milk SCC assist in directing milk quality control programs and assist with the identification of risk factors in herds. The production of milk with low bacterial counts starts at the farm and is influenced by many procedures related to farm management practices. At the farm level, microbial contamination of BTM occurs through three main sources; bacterial contamination from the external surface of the udder and teats, from the surface of the milking equipment, and from mastitis organisms within the udder (Murphy & Boor, 2000). The levels and types of microorganisms in BTM provide valuable information on the hygienic conditions during the steps of milk production. The microbiological count methods are used to monitor hygienic quality of raw milk including the total aerobic count (TAC). TAC is the most common method for the assessment of bacterial quality of raw milk, it estimates the total number of bacteria present at the farm´s pickup time, providing an overall hygienic milk-quality measure; however, it is limited for the identification of the bacteria contamination source. An alternative has been the standard plate count (SPC) and the preliminary incubation count (PIC), a selective count is measuring psychotropic bacteria, which will grow and multiply under improper refrigeration conditions. These organisms can create undesirable odors and off-flavors. Many psychotropic bacteria can also produce heat-stable enzymes that will survive pasteurization degrading and reducing milk and milk

products during shelf-life (Hayes & Boor, 2001). The laboratory pasteurization count (LPC), another selective count, estimates the number of thermoduric bacteria, mainly from the surfaces of poorly cleaned farm equipment that will survive a laboratory-scale batch pasteurization process. Thermoduric bacteria have been associated with spoilage of pasteurized milk. The Coliform count (CC) measures the number of coliform bacteria in milk, organisms primarily coming from the cow's environment, therefore high CC will give an estimation of the production sanitary status and practices. Coliforms can also incubate on residual films of improperly cleaned milking equipment (Reinemann *et al.,* 2003).

The results from a case–control study indicated that TAC and PIC were mostly related to cow and stall hygiene, whereas LPC and CC were related to equipment hygiene (Elmoslemany *et al*., 2009; Jayarao *et al*., 2004), and included among the bacteria groups associated with bovine IMI are *Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma spp, Streptococcus spp, Escherichia coli,* and SCN.
