Minimizing the level of Bacillus cereus spores in farm tank milk

In a year-long survey on 24 Dutch farms, Bacillus cereus spore concentrations were measured in farm tank milk (FTM), feces, bedding material, mixed grass and corn silage, and soil from the pasture. The aim of this study was to determine, in practice, factors affecting the concentration of B. cereus spores in FTM throughout the year. In addition, the results of the survey were used in combination with a previously published modeling study to determine requirements for a strategy to control B. cereus spore concentrations in FTM below the MSL of 3 log(10) spores/L. The B. cereus spore concentration in FTM was 1.2 +/- 0.05 log(10) spores/L and in none of samples was the concentration above the MSL. The spore concentration in soil (4.9 +/- 0.04 log(10) spores/g) was more than 100-fold higher than the concentration in feces (2.2 +/- 0.05 log(10) spores/g), bedding material (2.8 +/- 0.07 loglo spores/g), and mixed silage (2.4 +/- 0.07 log(10) spores/g). The spore concentration in FTM increased between July and September compared with the rest of the year (0.5 +/- 0.02 log(10) spores/L difference). In this period, comparable increases of the concentrations in feces (0.4 +/- 0.03 loglo spores/g), bedding material (0.5 +/- 0.05 log(10) spores/g), and mixed silage (0.4 +/- 0.05 log(10) spores/g) were found. The increased B. cereus spore concentration in FTM was not related to the grazing of cows. Significant correlations were found between the spore concentrations in FTM and feces (r = 0.51) and in feces and mixed silage (r = 0.43) when the cows grazed. The increased concentrations during summer could be explained by an increased growth of B. cereus due to the higher temperatures. We concluded that year-round B. cereus spores were predominantly transmitted from feeds, via feces, to FTM. Farmers should take measures that minimize the transmission of spores via this route by ensuring low initial contamination levels in the feeds (<3 log(10) spores/g) and by preventing growth of B. cereus in the farm environment. In addition, because of the extremely high B. cereus spore concentrations in soil, the contamination of teats with soil needs to be prevented.