SCC, BTSCC, BTC, SPC, PIC, LPC and CC are all tests that reflect the quality of the milk a farmer sells. Let’s look at them in more detail.
SCC means somatic cell count. Somatic refers to the body, so these are cells coming from the body. Most of the somatic cells found in milk are white blood cells, which are there in response to an infection. It is reasonable to assume that cows with a high SCC did, at one time, likely have one or more quarters infected with a pathogen, but cows can have elevated somatic cell counts at any time without having any detectable infectious organisms in the udder.
BTSCC is the bulk tank SCC. This is not the same measurement as a Dairy Herd Improvement Association SCC, which is the weighted average of the SCCs of all the cows in the herd. However, the two are usually pretty close in magnitude.
BTC, or bulk tank count/culture, is a count and speciation of all the organisms present in a known quantity of bulk tank milk. It is usually reported as CFUs (colony forming units) per cc of milk. One CFU will normally have thousands to many millions of bacteria within. A typical BTC report will quantify the numbers of Staph aureus, coagulase-negative Staph, Strep ag, non-ag Streps, coliforms and non-coliform gram negatives. The report may or may not include Prototheca and Mycoplasma counts. BTC can be used as kind of a report card on cow and milking time hygiene. Most of the environmental organisms, which are typically non-ag Strep, coagulase negative Staph and coliforms, get in the milk from the teat skin. Proper cleaning and drying will reduce contamination of bulk tank milk by these organisms. For the contagious organisms, including Staph aureus, Strep ag and Prototheca, most of the organisms in bulk tank milk come from the milk in the udders, so you can use the BTC to help determine if you have cows infected with these organisms. Note that there is crossover between contagious and environmental organisms. For example, Strep ag only grows in milk, so it is never an environmental, but non-ag Streps can grow in fairly high levels in some udders and is wildly found in cow manure, so the actual source of infection could be either another cow or the environment. Because of the high levels in the environment though, it is much more likely that the source is from there than from a cow. Prototheca is found in the environment, but it seems to behave as a contagious organism, meaning the more common source of infection is another cow.
SPC, or standard plate count, is the required count you get from the official lab once a month. It is simply a count of the total CFUs of all organisms present on an agar plate at 48 hours and represents the number of CFUs per ml of milk. In theory, your SPC should roughly equal the total count on your BTC, because they are counting the same organisms. The regulatory limit is 100,000, while industry standards are below 10,000, and samples from clean farms can be in the hundreds or low thousands. High SPCs typically arise from cleaning or incubation problems. Bacteria can double in numbers in 20 minutes at room temperature, so even a short failure of refrigeration can result in an elevated SPC, for example. While it is possible to have a high SPC caused by excess shedding from udders, this almost never happens.
LPC, lab pasteurized count or thermoduric count, counts the number of colonies that survive pasteurization. LPCs are often required by cheese manufacturers. Normal counts are usually below 200. Pasteurization kills most mastitis causing organisms, so high LPCs are also not normally caused by shedding from udders. A variety of organisms may cause high LPCs; most are organisms found in the environment of the cow. Some organisms may form biofilms, which are thin, slimy films that protect the organism from disinfectants. It may be possible to see or feel biofilms in tanks, lines or other equipment. LPCs are usually elevated because of cleaning problems or chronic buildup of biofilms or bacterial growth in milking systems.  
PIC, or preincubation counts, are performed by incubating milk at 55 degrees Fahrenheit for 18 hours and then counting the CFUs using SPC methods. This process selects for psychotropic, or cold-loving bacteria. PI counts should be below 10,000 and are important for ensuring good shelf life and reducing off flavors of milk. High PICs are often caused by Pseudomonas bacteria. Pseudomonas are notoriously difficult to kill with disinfectants. They are also commonly found in stored water, like cisterns or plastic holding tanks, for example. So, while high PICs are often associated with cleaning problems, contaminated water supplies can be part of the problem.   
CC, or coliform counts, are just a count of coliform CFUs on an agar plate and are part of the BTC procedure. By themselves, CCs represent bacteria that were on the teats when the units were attached, and high counts usually mean dirty cows, poor prep procedure or both. CCs should normally be below about 50.
All of the Cs count bacterial CFUs, except SCC and BTSCC. This is an important distinction. Your SCC does not immediately rise because someone did a poor job of prepping cows. Your BTC, SPC and CC will rise, though the SPC will not usually go beyond regulatory limits. SCC is not the appropriate monitor to compare parlor prep between shifts, for example. BTC, or just CC, are more appropriate tests for this situation. SCC looks for infected cows. Of all the Cs, the only other test that reliably indicates infected cows are the contagious part of the BTC.  
While sometimes it may seem that all of these Cs are a pain in the neck when a farmer just wants to sell milk, each one has a specific purpose. Understanding what they look for and what they mean can help keep those Cs low. That understanding may also help manage udder health on the farm.
Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.