Monday, May 19, 2014

On-farm Vulnerability to Post-
Pasteurization Contamination 

Here are the data:

Farm                               Pasteurized              Fed to Calves
   A first day                      400 cfu/ml               TNTC
   A second day                 0     cfu/ml               TNTC
   A third day                     200 cfu/ml               10,700 cfu/ml
   D                                  0     cfu/ml               16,700 cfu/ml
   E                                   0    cfu/ml                2,900  cfu/ml

Pasteurized counts were directly from the pasteurizer. Fed to calves were collected as the milk was being poured into the feeding pails.

On one hand, in all cases the pasteurizer was doing its job. The two positive counts could easily have been contamination while taking the samples. 

On the other hand, all the locations managed to add some bacteria to the clean pasteurized milk. Farms D and E added a mix of Staph species, Strep species and coliforms.

Farm A on the first two samples days had TNTC for both Staph and Strep species in the "as-fed" samples . In addition in excess of 5,000 cfu/ml coliforms were present. 

It will take some time to determine what happened on the first and second day to allow such high levels of post-pasteurization contamination. With no other facts in hand my best guess is that the wash cycle for the tank that is used to transport pasteurized milk to the calves did not function properly on days one and two.

While not the case on Farm A I did discover on another farm that the effectiveness of a transport tank wash cycle was related to wash water temperature. If the operator tried to wash the tank at a time too close to the parlor wash routine the water heaters had not yet recovered - water used to wash the transport tank was well below 120F.

On another farm the regular calf care person set up the wash equipment properly so that 10 washes per week were done well. The week-end relief person was inadequately trained to do this job. Thus, the transport tank did not clean correctly for the 4 week end feedings. 

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