**1. Introduction**

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

*of Food Protection* 67(12):2644-2650.

Yang, W., Zerbe, H., Petzl, W., Brunner, R. M., Günther, J., Draing, C., von Aulock, S., Schuberth, H.J., & Seyfert, H.M. (2008). Bovine TLR2 and TLR4 properly transduce signals from *Staphylococcus aureus* and *E. coli*, but *S. aureus* fails to both activate NFkappaB in mammary epithelial cells and to quickly induce TNF-alfa and interleukin-

Zadoks, R.N., Gonzalez, R.N., Boor, K.J., & Schukken, Y.H. (2004). Mastitis-causing *Streptococci* are important contributors to bacterial counts in raw bulk tank milk. *Journal* 

Zadoks, R.N., & Schukken, Y.H. (2006). Use of molecular epidemiology in veterinary practice. *Veterinary Clinics of North America: Food Animal Practice* 22(1):229–261.

8(CXCL8) expression in the udder. *Molecular Immunology* 45(5):1385–1397.

Milk conservation and its organoleptic quality are greatly affected by different microbial contaminants (Table 1). These microorganisms are present either directly on the animal, in the farm environment or on the milking equipment. Industry requirements and country regulations require that the number of bacteria in raw milk be under a specific amount, often of 100 000 bacterial cells ml-1. Recent bacterial counts from a survey in Québec (Canada) found that most raw milk samples were under 50 000 bacterial cells ml-1 (http://www.lait.org/fichiers/RapportAnnuel/FPLQ-2010/controleQualite.pdf).

Contamination of raw milk by *Clostridium* may cause important economic losses in specific type of cheese, mostly hard and semihard cheeses. Epidemiologic studies demonstrated that silage was in close relation with the raw milk contamination by *Clostridium* (Klijn et al., 1995).


**Table 1.** Example of microbial contaminants of raw milk
