Bacteria-Milk Quality Concerns
Bacteria in raw milk cause several concerns. There is the concern that a potentially dangerous human pathogen may enter raw milk and lead to problems. This issue always has to be recognized and monitored due to the obvious public health concern. A far more common problem however is the presence of bacteria in raw milk that cause some reduction in product quality making it less acceptable for processing and eventual consumption. As bacteria grow they may damage milk components causing off-flavors because of damage to the protein or milk fat. Other bacteria may cause milk to sour and become acidic. Certain species can cause milk in cooling tanks to develop stringiness as they produce a mucilage type material. Certain bacterial contaminants and their associated enzymes and toxins may even survive pasteurization and create problems in manufactured milk products.

Extended Milking Times -- Large Dairies
Many dairy farms now milk hundreds or thousands of cows daily and so there is plenty of opportunity for problems. One issue is simply the prolonged length of milking times on the large dairies. Smaller dairies may have a 2-3 hour milking time after which the system is thoroughly washed. It is then idle for 8-10 hours between milkings. Large dairies have just the opposite problem. They may have 45 minutes, maximum, to wash the system and then it is back in service for another 8-10 hour period of milking.

Bacteria need only a few basic things for survival and growth. Food and water are essential and milk provides these needs. They also favor certain ranges in temperature. While this varies by bacterial species, warm conditions in a milking system during milking encourage bacterial growth. The last element in determining total bacterial growth is time. The longer the opportunity to grow under optimal conditions the greater the resulting concentration.

Extended milking times result in milk-film buildup on system components such as filters, liners, rubber tubes, sensing devices etc. When this occurs, bacteria that may be present, can grow rapidly in the warmth and adequate food supply that is present. As a result, a long milking time can be a factor in the bacteria count of raw milk simply because it allows bacteria to grow with few restrictions over a span of 8-10 hours. As milk continues to pass over these areas it becomes contaminated as it moves to the cooling/holding tank.

Ending milking and rinsing and then washing the system with hot alkaline solutions eliminates the majority of food and bacteria that may be associated with surface films. The use of an acid rinse following the alkaline wash renders the local conditions relatively acidic which hinders bacterial growth. Finally, use of a sanitizer prior to the next milking kills a high percentage of any residual bacteria that may have grown between milkings. In operations with very limited downtime, use of an acid sanitizer is an effective way to accomplish both objectives in one step. Long milking cycles means greater intervals between wash-ups and this increases the risk of high bacterial counts. It also means every washup has to be done correctly with the proper dose of the proper chemicals because the next opportunity won't occur for another 10-12 hours. There is no room for error.

Water Related Bacteria Problems
Occasionally a raw milk bacteria problem develops that is very difficult to sort out. Some dairies have water sources that may on occasion become contaminated with bacterial species suited to living and growing in water supplies. This includes water from wells, springs, and water capture/storage devices such as cisterns or tanks. The water supply may generally meet the requirements for potable water and have acceptable coliform counts but due to a variety of causes it may on occasion become contaminated. This may occur as a result of contaminated surface water somehow entering the system or it may happen while water is held in storage vessels for a period of time allowing bacterial numbers to increase. 

Pseudomonas species are a category of bacteria frequently found on the interior surfaces of pipes and storage containers and they can be introduced into the milk inadvertently as the system is hosed down with such water. These bacteria have the ability to grow at refrigeration temperatures and can cause a major increase in preliminary incubation (PI) counts. If introduced into the milk they will grow and cause problems even if the cooling system is operating adequately. Pseudomonas species are one of the dominant environmental bacteria contaminants of raw milk and they are typically associated with contaminated water sources.

Appropriate microbiological testing of such water supplies by a competent laboratory is the only practical way to establish the bacterial status of water used in the parlor and milk house. Practically any water supply may contain Pseudomonas. It has the capacity to cling to and coat the interior surfaces of pipes, tanks etc. So long as these coatings are undisturbed there may be little trouble but if the lines are disturbed for some reason, such as construction or whatever, they may be released in large quantities and can lead to problems. Species of Pseudomonas are also capable of causing a difficult to treat form of mastitis. Fortunately Pseudomonas mastitis occurs relatively infrequently.

Long milking times cause the bacteria count to gradually rise as the milking proceeds. Occasionally on farms there is a need to divert milk from the latter part of the milking into a separate tank because the main tank is full. In this instance the overflow milk, placed in the alternate tank, would have the highest concentration of bacteria of all the milk harvested during that milking. It would consist only of milk that had passed over surfaces that would have been in use for many hours and likely experienced bacterial buildup. 

Milk samples from the two tanks may show significantly different bacteria counts. The bacteria count of the overflow tank milk could be much higher than the main tank for this reason.

Dirty Milk Contact Surfaces
Any time milk contacts surfaces that are not normally cleaned and which may be dirty, problems can quickly develop. A split liner will allow milk to enter the pulsation chamber, a space which is not cleaned and is not intended as a milk contact surface. As pulsation occurs the dirty, bacteria laden milk in this area may contaminate the milk passing through the liner. This situation impacts both milking performance and milk quality. Monitor the system routinely and make certain rubber goods and other wear parts are changed according to a regular schedule.

A liner split may allow some milk to pass into the pulsation line and once there it is very difficult to clean. Milk may be deposited in distribution and balance tanks. This material can develop huge bacteria numbers and if it somehow enters the normal milk contact side of the system it can create elevated bacteria counts in the raw milk.

Milk pump seals that leak can lead to problems. As milk leaks out past the seal it contacts dirty surfaces and there can be some interface with the milk side of the system. A cheesy looking buildup on the impeller shaft of the milk pump indicates a need for repairs or replacement. This situation, if not fixed, can result in contamination and bacteria count problems.

Each of these issues tends to be related to problems in some component of the system. They are unpredictable and may occur at any time. Avoidance requires scheduled monitoring of each of these potential problem issues by someone who is trained to know what to look for.

Bacteria Count Benchmarks
Bacteria counts, in farm tank milk, are a function of bacteria quality of the raw milk as it exits the cow, sanitary status of all milk contact surfaces from the teat end to the bulk tank, cooling efficiency and external sources of contamination that may enter the system. The benchmark for quality raw milk should be a standard plate count of less than 10,000/ml. Most high quality dairy farms routinely achieve bacteria counts of 5,000/ml or less. It is possible to regularly achieve low bacteria counts and if these levels are not being attained take a hard look at each and every component involved, especially the ones noted.

There are generally significant economic consequences when raw milk bacteria counts are out of line due to either making or not making bonuses. Typically both the somatic cell counts and bacteria counts have to meet certain standards in order for any bonus to be earned. An excellent somatic cell count, combined with an unacceptable bacteria count, could result in bonuses being lost or reduced. With the relatively high milk prices of the past few years the bonus incentives may not seem as great, on a percentage basis, but on an actual dollar basis it can still represent serious money for all dairies regardless of size. It pays to monitor issues such as the ones discussed to minimize the risk of an unexpected increase in milk bacteria counts that could eliminate bonus payments.