MILK QUALITY MEASURES

Standard Plate Count (SPC)
The SPC is the total quantity of viable bacteria in a millimeter (ml) of raw milk expressed as CFU/ml (colony forming units per ml). The bacteria are counted but not specifically identified. The SPC is performed on milk samples collected from the bulk tank. This is usually done at least monthly by the milk processing plant. The SPC is primarily an indicator of the sanitation used by milkers as they milk the cows, the capacity of the equipment to rapidly cool the milk to less than 40 F within 2 hours after milking, and the cleaning and sanitizing of the milking equipment.

Laboratory Pasteurized Count (LPC)
The LPC is the measure of bacteria that survive after pasteurization in the finished milk products. These bacteria come from the environment of the cow (Streptococcus sp. and the coliforms) and incubate on the milking equipment. These surviving bacteria produce off flavors and reduce the shelf-life of dairy products. The LPC is performed on bulk tank milk samples at least once per month by most milk processors. The LPC generally reflects the sanitation level during milking and the adequacy of the milking system cleanup between milking periods. Worn rubber liners or gaskets may harbor bacteria and contribute to the LPC count. The LPC and the coliforms counts may be elevated with wash-up problems.

Coliform Count

The coliform count reflects the ex- tent of fecal bacteria in the milk. The coliform count is performed on raw milk samples from the bulk tank. Coliform counts are usually performed at least monthly by the milk processor. The col- iform count may reflect milking cows with wet, manure soiled udders and teats or growth of coliforms within the milk- ing system. Cows with coliform mastitis rarely influence the coliform count.

The coliform counts may be elevated when milkers fail to properly clean and dry the udder and teats prior to milking. Counts may be elevated when dirty milking equipment is used to milk the cows or when the water source is contaminated.

Preliminary incubation count (PIC)

The PIC count is a measure of bac- teria that will grow at refrigerator tem- peratures. The PIC gives an indication of the on-farm sanitation and holding temperatures of the milk in the bulk tank. It is similar to the SPC in that it is performed on raw milk from the bulk tank; however, in the PI testing the milk is held at 55 F for 18 hours before cul- turing in the same method as the SPC.

Sediment

Sediment is a measure of the cleanliness of the cows being milked. Sediment is the fine debris that is capable of moving through the milk filter into the bulk tank milk. High sediments may also be associated with high bacteria counts.

Sediment may enter the milk when extremely fine sand is used in the bedding materials of the cow housing. It may also enter the milk when the milkers are not using water to clean the udders and teats prior to milking.

Added water
The milk is tested by the milk processor for added water using a reezing point test. When water is added to the milk, the freezing point will be altered. Added water is commonly found when water is accidentally left in the milking system between milkings.

Antibiotic drug residues

Antibiotics are commonly used to treat mastitis or other conditions in dairy cows. Each antibiotic has label instructions that indicate the approved reasons for using the antibiotic, the dose or amount of the antibiotic, how often the antibiotic dose should be repeated, the route of administration, and the type of cow permitted to be treated with the antibiotic. Each antibiotic preparation also has a specific withdrawal time for both milk and meat. The withdrawal time is the time from the last treatment with the antibiotic until the milk is permitted to be put in the bulk tank for shipment to the processor.

Antibiotic residues occur when employees fail to follow the specific label instructions when treating cows.

Somatic cell counts (SCC)
Low levels of somatic cells are normally found in milk (<100,000 cells/ml). The somatic cell count can be measured on bulk tank milk or milk from individual cows. When mastitis occurs in a cow, the somatic cell count (SCC) in the milk for that cow will increase in approximate proportion to the severity of the infection within the udder. Milk production is inversely related to SCC. An elevated SCC in a particular cow will also influence the somatic cell count of the bulk tank milk (BTSCC). Elevated BTSCC will reduce the quality of the milk from the herd resulting in lowered herd milk production, loss of quality milk premiums, reduced cheese yields and decreased shelf-life of the finished products.

Clinical mastitis
Clinical mastitis is the form of mastitis that is visibly apparent to the milkers. Clinical mastitis will result in abnormal milk (flakes, clots, watery) and possibly signs of sickness in the cow as well. Milk from cows with clinical mastitis should not be milked into the bulk tank milk for sale. Milk from cows with clinical mastitis will also have elevated SCC and be of poor quality. Cows detected with clinical mastitis should be segregated from the milking herd and handled according to the herd protocol. Early detection and treatment of clinical mastitis can be expected to reduce the incidence of chronic, non-responding cases of mastitis.