David Gleeson, Paul Edwards and Bernadette O’Brien
The objective of this study was to investigate the effect of omitting teat preparation prior to milking on the bacterial levels in milk directly after milking and after a period of milk storage. Eighty Holstein–Friesian dairy cows were assigned to two pre-milking teat preparation treatments: (i) washing of teats and drawing of foremilk, followed by drying with paper towels and (ii) no teat preparation. Individual cow measurements included individual quarter somatic cell count (SCC) and teat swabs for the presence of Bacillus cereus sensu lato. On seven monthly occasions, all milk produced over a 24 h period from each treatment group was segregated into a separate tank and sampled. Sub-samples of this milk were stored at 4 °C for 0, 24, 48 and 72 h, and the milk was analysed for total bacterial count (TBC), thermoduric bacterial count and the presence of B. cereus s. I. Individual quarter SCCs were numerically higher for unprepared teats (159,000 cells/mL) compared with those for prepared teats (133,000 cells/mL; P < 0.09). A similar trend was observed for bulk tank SCC, with the unprepared teat treatment tending to have a higher SCC (155,857 cells/mL) compared to the prepared teat treatment (102,286 cells/mL; P< 0.09). The TBC was not significantly higher from unprepared teats (3,152 cfu/ mL) compared with milk from prepared teats (1,678 cfu/mL) (P< 0.10). Milk TBC was significantly higher after storage for 72 h compared with that after 0, 24 and 48 h (P< 0.01). The results of this study indicate that under good hygienic conditions in an outdoor grazing situation, the omission of pre-milking teat preparation has a minimal effect on TBC and SCC.
L.F. Paludetti, K. Jordan, A.L. Kelly and D. Gleeson
In this study, the effect of storage temperature (2 or 4°C) on the composition of milk and microbiological load was investigated over 96 h. Milk samples were collected from farm bulk milk tanks after one complete milking and stored at 2 or 4°C over 96 h. Total bacterial count (TBC), psychrotrophic bacterial count (PBC) and proteolytic bacterial count (PROT) were affected by storage time and temperature and varied significantly between farms (P < 0.05). The levels of TBC, PBC and PROT bacterial count increased from 4.37 to 6.15 log cfu/mL, 4.34 to 6.44 log cfu/mL and 3.72 to 4.81 log cfu/mL, respectively, when the milk was stored for 96 h at 2°C. The milk samples stored at 4°C had higher increases in these bacterial counts after 72 h in comparison to milk samples stored at 2°C. The casein fraction content was lower in milk samples stored at 4°C, which could be due to high levels of PROT bacteria or enzyme activity in these samples. Milk stored for 96 h at 2°C has less impact on composition or processability parameters compared to milk stored at 4°C.
A. O’Connell, E.M. Lawton, D. Leong, P. Cotter, D. Gleeson and C.M. Guinane
The objective of the study was to isolate potential Bacillus cereus sensu lato (B. cereus s.l.) from a range of farm environments. Samples of tap water, milking equipment rinse water, milk sediment filter, grass, soil and bulk tank milk were collected from 63 farms. In addition, milk liners were swabbed at the start and the end of milking, and swabs were taken from cows’ teats prior to milking. The samples were plated on mannitol egg yolk polymyxin agar (MYP) and presumptive B. cereus s.l. colonies were isolated and stored in nutrient broth with 20% glycerol and frozen at -80 °C. These isolates were then plated on chromogenic medium (BACARA) and colonies identified as presumptive B. cereus s.l. on this medium were subjected to 16S ribosomal RNA (rRNA) sequencing. Of the 507 isolates presumed to be B. cereus s.l. on the basis of growth on MYP, only 177 showed growth typical of B. cereus s.l. on BACARA agar. The use of 16S rRNA sequencing to identify isolates that grew on BACARA confirmed that the majority of isolates belonged to B. cereus s.l. A total of 81 of the 98 isolates sequenced were tentatively identified as presumptive B. cereus s.l. Pulsed-field gel electrophoresis was carried out on milk and soil isolates from seven farms that were identified as having presumptive B. cereus s.l. No pulsotype was shared by isolates from soil and milk on the same farm. Presumptive B. cereus s.l. was widely distributed within the dairy farm environment.