The effect of bulk tank and milking machine cleaning procedures (determined from a questionnaire) on bacterial contamination of 48-hour refrigerated milk was examined in 24 herds. Milk samples were analyzed for standard plate count (SPC) and for total coliform, Staphylococcus aureus and Streptococcus agalactiae contamination. Milk samples from 14 herds were cultured for Salmonella and Listeria monocytogenes. Geometrical means of SPC were <1.0×10(6) UFC/ml in 20 herds, <7.5×10(5) UFC/ml in 19 herds and <1.0×10(5) UFC/ml in 11 herds. Geometrical means >10³ UFC/ml of total coliforms were observed in seven herds. S. aureus and S. agalactiae were found in 22 and 12 herds, respectively. Salmonella and L. monocytogenes were not found in any of the samples. The use of alkaline and acid detergents plus sanitizing was associated (P<0.05) with SPC <1.0×10(5), and the use of either alkoline or acid detergent or sanitizing or no chemical product was associated with SPC >5.0×10(5) UFC/ml.
milk quality; microbiology; equipment cleaning procedure; standard plate count
