Keeping Pasteurized NonSaleable Milk Clean
A study of 618 dairies in the US looked at post-pasteurization bacteria levels in calf milk.
Even when the pasteurizer was working well (that is, less than 20,000 cfu/ml coming right out of the pasteurizer) 49% of the samples increased in bacteria count by the time the last calf was fed. That is almost one-half of the samples went UP in bacteria count.
For the moment let's assume that you have this problem - a high post-pasteurization contamination level. And, let's assume you are at least trying to wash equipment to reduce this problem (right temperature water, proper chemicals, correct wash time).
Some of the favorite places where bacteria hide?
1. If you have any sort of tank or closed container, check out the inside surface of the top. I frequently find that mechanical wash systems do not clean these surfaces consistently and well. Often the only solution is manual scrubbing with a brush.
2. Pumps - if the feeding system has a pump, this piece of equipment is not always part of the mechanical wash cycle - the pump has to have circulating rinse, wash and acid rinse water in order to clean well, not just an end-of-wash pump out.
3. Joints in plumbing - many of our milk-feeding systems are constructed with plumbing fittings from the hardware store, not the milking equipment dealer. Any joint that cannot be broken down (the kind that has a release clip with a gasket and comes completely apart) is a perfect site for milk residues to build up, collect bacteria, grow bacteria and release bacteria into the milk supply. The only solution I know of is periodic tear downs and scrubbing.
4. If you feed with bottles the favorite places are the inside of nipples and the inside shoulder of the nursing bottle.
Just for review, the recommended protocol on washing milk containers is found HERE (Spanish version is HERE).
Just to review, the ideal samples for identifying these contamination issues are:
1. Raw milk (before pasteurizing)
2. Direct from pasteurizer
3. First calf fed - "as-fed" sample
4. Last calf fed - "as-fed" sample
An "as-fed" sample is one taken as the milk flows into the feeding bucket. If you feed with bottles the "as-fed" sample is taken from the end of the nipple just before the bottle is given to a calf.
Reference: Yoho, W.S.B, and Others, "Variation on nutrient content and bacteria count of pasteurized waste milk fed to dairy calves." American Journal of Dairy Science Supplement T132, 2017.