Sunday, March 16, 2014

Persistent Post-Pasteurization 

The dairy houses calves in individual pens and feeds pasteurized milk twice daily in pails at the front of the pens. The results just came back from the laboratory. Post-pasteurization bacteria contamination levels are down in milk being fed to calves. Good job. 

We changed the transport tank wash routine using hotter water so that the discharge water is over 120F. The transport tank, pump, hoses and nozzle now wash in a cycle for 10 minutes - after the transport tank is loaded with the hot detergent solution the feeding pump is turned on and the nozzle is propped open and stuck into the hatch opening at the top of the transport tank. Bacteria counts in milk being fed to calves dropped from  200,000cfu/ml to 2,000cfu/ml. That is great.

They are still at 2,000cfu/ml Klebsiella bacteria. And we are feeding 6 quarts of this per day to calves less than a week old. Let's see - 6 quarts is about 5,700ml. If I multiply 2,000cfu/ml times 5,700 ml I get 11,400,000 Klebsiellaa bacteria fed daily. Not so great.

Milk coming from the pasteurizer grows nothing - nada - zip. Why the persistent contamination  being fed to calves?

So, what are the suspected sources of post-pasteurization contamination now?

First, I discovered that the 24 inch hatch at the top of the transport tank was being left open after the tank was washed. That is correct. Left wide open for somewhere between 9 and 13 hours between uses. Well, how clean in the air in a shed connected to a barn full of adult cows?

What would if find it I took a blood agar plate into this barn, lifted off the lid and set it down for 5 minutes? When incubated properly this plate would grow a great crop of bacteria. Cow barn air is loaded with bacteria. Recommendation? Keep the lid closed after the tank is washed.

Second, I checked to see if my recommendation about tearing down the plumbing had been accepted. No. The plumbing for this transport tank, hoses and feeding nozzle are all galvanized steel fittings - no stainless steel anywhere. Everything screws into the next piece. Guess what we will find when we tear this down? A ring of tan residue (biofilm loaded with bacteria) where every fitting screws into the next one.

Short term stop gap action (not including tearing everything apart which will be a big job) is to add a sanitizing step.  This is done just before filling the transport tank with pasteurized milk. Plenty of 170F water, enough chlorine sanitizer to get the chlorine level up to about 500ppm and let it circulate for about 5 minutes. Remember that bacteria kill with a sanitizer is directly related to temperature, concentration of oxidizing agent and duration of exposure.

Well, we are scheduled to collect two sets of milk samples at the end of next week (we collect from the same batch raw, pasteurized, first calf fed and last calf fed samples) from AM and PM feedings. Maybe these coliform counts will be lower.

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