@Dsth had it pretty much in a nutshell.
I work for DHIA...30+ years as a milk tester.. now we are called "supervisor technicians", looks good on paper!
We are a management tool for a dairy farmer. They give us info and we collect milk samples and they get back a report that basically tells them the value of a cow in the herd. The more info they give us, the more complex the info they get back and the more accurate the value of the cow in their herd. This is a comparison of their own cows, there are a few generalized graphs and things comparing overall herds, but this is for the farmers OWN use.
When this was first started you went to a farm 2 consecutive milkings; to give an accurate accounting for a cow's production in 24 hours. I use special meters that are attached to the milk hose coming from each cow, it collects a sample of milk through the calibrated meter, and the sample gets sent to the lab for all that dsth said, for the basic test... SCC is somatic cell count; basically it is measuring how "clean " the milk is of infectious things like staph and strep, things that exist in every human and mammal's milk.. the key is to what percentage as high scc is an indication of an infection. Infection means mastitis.
But the key is the low percentage of scc means milk will keep longer.
Long shelf life is important in the "fluid milk market", some of what
@sstterry was referring to. Here in the southeast most of our milk goes to the fluid milk market, drinking milk; and the lower the scc, the longer it will be able to sit on the shelf in the store and be "fresh" and not go bad. Milk has a sell by date... and SHOULD be good for at least a week after. It will stay good in the fridge longer. For example, when I do not have any of my own cows milking, I get my milk from a former dairyman that keeps a few cows still. He got out after getting hurt and several surgeries. His farm was always coming in 1st or 2nd in our area assoc every year for the lowest scc... attention to detail, cleanliness, and culling cows that were high scc cows. His milk will often keep 3 weeks in the fridge and still taste fresh; raw milk, not pasteurized.
The scc count is more important for anyone that consumes raw milk, because it means healthier milk to drink.
Milk in the Wisconsin area, is mostly for cheese processing, and undergoes more processing and gets paid for differently than fluid milk. It is called cheese yield. However, most of the milk also gets more premiums for higher butterfat and for higher solids non-fat that is important to cheese making. I am not an expert on the different federal milk marketing orders; but it determines the amount of money that must be paid for the milk, minimum.. and yes, some of the rules on what the dairy processing companies can use and not use. Dairy Farmers of America (DFA); Maryland-Virginia; and Land o Lakes, are the 3 companies that a dairy farmer has access to in this area. You HAVE to belong to one of the companies in order to sell milk. Today they are very picky about who they take on; and are pushing the small farmer out by charging more and more for small farm "pickup stops".
What most farmers that start testing are looking for is the SCC counts. The truck that picks up milk takes a sample of the tank before they pump it on the tanker; that sample along with any other farms they have picked up at, are run through the lab at the milk plant, BEFORE the truck is unloaded... they are looking for #1 antibiotics. FIRST MOST CRITICAL, and the amount allowable is miniscule in PPB (parts per billion)... #2 scc... because a high cell count can affect what the milk is used for... at that plant OR in some cases, the milk can be sent to a manufacturing plant to salvage. If it passes the tests... the tanker is unloaded into the silos that the milk is kept in to use as the plant processes the milk and packs into the qts and gallons that you get at the store.
Many farms have started testing because their tank scc is high, and a representative from the company they ship to, comes and says, you have to find out what cows are contributing the high scc, either cull them, or they need to be treated.. they will refuse to pick up the milk if it is not remedied. Limits used to be 1,000,000 scc count; dropped to 750,000 and now is 500,000; AND the milk companies pay a premium for low scc counts.
Example; these are round figures... 250,000 is considered the average top amount allowed. Paying $20.00 per hundred lbs of milk (gallon is approx 8.6 lbs... 12 gallons= 100 lbs) with 3.5% butterfat... butterfat is worth 3.00 at the average.
Farmer ships milk at 125,000 scc... he gets $.10 MORE per hundred...ships under 90,000 scc he gets $.25 more per hundred... That can translate into $50 -$200 more PER pickup...milk is picked up normally every other day... usually 4 milkings is standard. Well at 15 average pickups a month... at say $100 per pickup that's an extra $1500 a month.
Say the farmer is shipping 10,000 lbs a pickup... average for 75 good milking cows that are averaging 65-70 lbs a day...$20/100 lbs = $2,000 every pickup....add another $100 PER PICKUP for no extra costs... just good quality milk from paying attention to details and having good quality milk.
On the flip side, if the scc is over 250,000 they DEDUCT from the amount paid... so you are losing $100 to $200 per pickup... that's a chunk of money at the end of the month. And some companies will "cut you off" and refuse to pick up if you have too many times of over the limit. I am thinking that they are actually down to 400,000 limits now.
So, by testing the individual cows, the farmer can find out which ones are contributing to the problem.. and part of the reports they get back lists the highest scc cows and what percentage of the high tank counts they are contributing... it depends on if they are making alot of milk or not... Also, there are cows that are chronic high scc ones... and those cows are often treated and a couple months later have high cell counts again... those are often high staph or strep cows and it is in their systems, and they should be culled if they cannot be cleared up...not enough to make the cow sick, but enough to make the milk constantly show up as high counts.
Add into that, the farmer is getting more for higher fat percentage also, so a low scc and high butterfat shipment can net a farmer a couple thousand EXTRA in their check every
month.
Getting back to what I do. So, I get a milk sample from every cow that goes through the milking, and it is sent to the lab and checked. I also record any pertinent information on the cows. Calving dates, dry off dates, heat dates, breeding dates, vet preg checks, cows leaving farms and reasons, sold, died whatever. We can also record more management tools like hoof trimmings, shots given; all sorts of other protocols done on the farm. There are more an more farmers... doing their own recording of these things through one of our programs on their own computers that are in the dairy farm office... because farmers are getting bigger and bigger and they need this stuff up to date on a daily or weekly basis, not once a month like when we come test. They can record things daily and get all sorts of lists generated for things like when to watch for a cow to come in heat, lists of the next ones to go dry for 30 days out; lists of due to calves so they can group according.
With the advent of computers, they can print out daily or weekly lists as needed; they have access to the results of the milk testing within 24 hours of the samples being processed at the lab; they don't have to wait for the mail to bring the results.
With all this info, a farmer can go through and make culling decisions. It is not always based on milk production... Say you have a cow milking 100 lbs avg a day and another one making 65 lbs a day... 100 lbs a day says better? BUT...the one making 100 lbs a day has a high scc AND you have had to treat her for mastitis 3 times in 3 months...and her milk CAN NOT go in the milk tank... so is discarded. Even with high production, she is not making money those days her milk is kept out of the tank...The one making 65 lbs has a real low scc count and never needs treating... she is not making as much milk but is actually contributing more to the income REGULARLY.
As in beef cattle...the ideal dairy cow calves every 12 months... 2 months dry period and 10 months producing. A high producing cow often will not breed back as fast as her "body" is focusing on milk production and they often will not cycle. because she is in a net negative energy balance; putting out more than she can eat and put back into her body... reproduction is one of the first things to "shut down" when not in a positive energy balance. Same as a beef cow; she is producing milk for the calf, it is cold, the feed isn't as great; and she will not come back in heat at 60 days because her body is dictating that she cannot make milk to feed the calf, gain weight back and get pregnant.
This is why dairy cows are fed the concentrated rations they are fed, and the feed consultant business is so important to dairy farmers, to get the max out of the cows ALL THE TIME
So, a cow making a little less milk, low scc, breeds right back and calves every 12 months, may very well make more money than a high producer with scc/mastitis problems and calves every 15 months.
That said, many high producers that do not have a scc problem, make money even when calving every 15 months.
The information that gets compiled through DHIA testing, gives that to the farmer, all in one place, and ranks his cows against their herd mates in his herd.
